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1
Chan, Simon Hang Chi. "Bond and cracking of reinforced concrete." Thesis, Cardiff University, 2012. http://orca.cf.ac.uk/36698/.
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Ribbed reinforcement is described as “high bond” in Eurocode 2 (EC2) and within the code serviceability checks make no allowance for variations in either the ductility or bond characteristics of these bars. In this work, this matter is explored, and the crack development and behaviour of concrete beams reinforced with various types of ribbed steel bar are investigated, using both numerical and experimental approaches. The objective of the experimental approach is to undertake a series of experiments to compare the performance of beams made with standard reinforcement with that of beams formed with a new high-ductility bar produced by CELSA UK. The relationship between the bond strength and the rib pattern of reinforcing steel was studied and the behaviour at SLS load levels of RC beams with reinforcement of different rib patterns in flexure is discussed. The cracking of beams was monitored both visually and using a non-destructive Digital Image Correlation system to trace in-plane deformations and strains on the surface of the specimens. The test results showed that specimens with bars which had the highest relative rib area (fR value) exhibited the smallest crack spacing and crack width. A numerical model was developed to explore the crack development of reinforced concrete beams under flexural loading. The model employed a non-linear material model for concrete and a smeared crack approach. In order to address the well known numerical stability problems, associated with softening models, a non-local gradient method was used. Crack widths cannot be obtained directly from such models, due to the diffuse nature of non- local simulations, therefore a post-processing procedure was developed to allow the crack characteristics to be calculated. Several numerical examples are presented to illustrate the satisfactory performance of the model. In addition, a series of numerical simulations of the BOND AND CRACKING OF REINFORCED CONCRETE Simon H.C. Chan Page vi experimental beams tested in the present study were used validate the numerical model and conversely, to provide confidence in the consistency of the experimental results.
2
Momeni, Amir Farid. "Y-cracking in continuously reinforced concrete pavements." Thesis, Kansas State University, 2013. http://hdl.handle.net/2097/15642.
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Master of ScienceDepartment of Civil Engineering
Kyle A. Riding
When transverse cracks meander there is a high possibility for transverse cracks to meet at a point and connect to another transverse crack, creating a Y-crack. Y-cracks have been blamed for being the origin of punchouts and spallings in CRCPs. When the direction of maximum principal stress changes, it could cause a change in the crack direction, potentially forming a Y-crack. Finite Element Models (FEMs) were run to model the change in principal stress direction based on design and construction conditions. The finite element model of CRCP using typical Oklahoma CRCP pavement conditions and design was assembled. The model included the concrete pavement, asphalt concrete subbase, and soil subgrade. The effect of areas of changed friction on the direction of principal stress was simulated by considering a patch at the pavement-subbase interaction. Investigated factors related to this patch were location of patch, friction between patch and subbase, and patch size. Patches were placed at two different locations in the pavement: a patch at the corner of the pavement and a patch at the longitudinal edge between pavement ends. A change in the friction at the corner had a large effect on the stress magnitude and direction of principal stress, while a patch in the middle did not significantly change the stress state. Also, patch size had a noticeable effect on stress magnitude when the patch was at the corner. Another model was developed to understand the effect of jointed shoulder on direction of maximum principal stress. Analysis of this model showed that the stresses were not symmetric and changed along the width of the pavement. This meandering pattern shows a high potential for Y-cracking. Also, several finite element models were run to understand the effects of different shrinkage between mainline and shoulder. In order to simulate the effects of the differential drying shrinkage between the hardened mainline concrete and the newly cast shoulder, different temperature changes were applied on the mainline and shoulder. For these models, the orientation of the maximum principal stress was not significantly changed from different amounts of temperature decreases between mainline and shoulder. Also, effect of different longitudinal steel percentages was investigated by comparing two finite element models with different steel percentage. The model with higher steel percentage (0.7%) indicated more variation in stress, potentially leading to more crack direction diverging.
3
Nejadi, Shamsaddin Civil & Environmental Engineering Faculty of Engineering UNSW. "Time-dependent cracking and crack control in reinforced concrete structures." Awarded by:University of New South Wales. School of Civil and Environmental Engineering, 2005. http://handle.unsw.edu.au/1959.4/22440.
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Due to the relatively low tensile strength of concrete, cracks are inevitable in reinforced concrete structures. Therefore, studying the cracking behaviour of reinforced concrete elements and controlling the width of cracks are necessary objectives both in research and in design. The introduction of higher strength reinforcing steel has exacerbated the problem of crack control. Using higher strength steel, means less steel is required for a given structure to satisfy the strength requirements. The stiffness after cracking is reduced and wider crack widths will occur under normal service loads. Unserviceable cracking may encourage corrosion in the reinforcement and surface deterioration, and may lead to long term problems with durability. Indeed excessive cracking results in a huge annual cost to the construction industry because it is the most common cause of damage in concrete structures. In this study cracking caused by both shrinkage and external loads in reinforced concrete members is examined experimentally and analytically. The mechanisms associated with cracking and the factors affecting the time-varying width and spacing of both direct tension cracks due to restrained shrinkage deformation and flexural cracks due to the combined effects of constant sustained service loads and shrinkage are examined. Laboratory tests on eight fully restrained slab specimens were conducted for up to 150 days to measure the effects of drying shrinkage on the time-dependent development of direct tension cracks due to restrained deformation. The effect of varying the quantity, diameter, and spacing of reinforcing steel bars was studied. In addition, an analytical model previously developed without experimental verification by Gilbert (1992) to study shrinkage cracking was modified and recalibrated. A second series of tests on twenty four prismatic, singly reinforced concrete beams and slabs subjected to monotonically increasing loads or to constant sustained service loads for up to 400 days, were also conducted. The effects of steel area, steel stress, bar diameter, bar spacing, concrete cover and shrinkage were measured and quantified. An analytical model is presented to simulate instantaneous and time-dependent flexural cracking. The tension chord model (Marti et al, 1998) is modified and used in the proposed model to simulate the tension zone of a flexural member and the time-dependent effects of creep and shrinkage are included. The analytical predictions of crack width and crack spacing are in reasonably good agreement with the experimental observations.
4
Peterson, J. Eric. "A time to cracking model for critically contaminated reinforced concrete structures." Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-08042009-040446/.
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5
McLeod, Christina Helen. "Investigation into cracking in reinforced concrete water-retaining structures." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/80207.
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Thesis (MScEng)--Stellenbosch University, 2013.Durability and impermeability in a water-retaining structure are of prime importance if the structure is to fulfill its function over its design life. In addition, serviceability cracking tends to govern the design of water retaining structures. This research concentrates on load-induced cracking specifically that due to pure bending and to direct tension in South African reinforced concrete water retaining structures (WRS). As a South African design code for WRS does not exist at present, South African designers tend to use the British codes in the design of reinforced concrete water-retaining structures. However, with the release of the Eurocodes, the British codes have been withdrawn, creating the need for a South African code of practice for water-retaining structures. In updating the South African structural design codes, there is a move towards adopting the Eurocodes so that the South African design codes are compatible with their Eurocode counterparts. The Eurocode crack model to EN1992 (2004) was examined and compared to the corresponding British standard, BS8007 (1989). A reliability study was undertaken as the performance of the EN1992 crack model applied to South African conditions is not known. The issues of the influence of the crack width limit and model uncertainty were identified as being of importance in the reliability crack model.
6
Sudoi, Elias K. Nasrazadani Seifollah. "Factors influencing horizontal cracking in continuously reinforced concrete pavements (CRCP)." [Denton, Tex.] : University of North Texas, 2008. http://digital.library.unt.edu/permalink/meta-dc-9025.
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Ulbinas, Darius. "Cracking and stiffness analysis of steel fiber reinforced concrete members." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2013. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2013~D_20130211_185704-20674.
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In last decades, fibre reinforcement is widely used in many countries as ad-ditive for concrete and cement mortar mixture for production of structures. Fibre reinforcement applications in Lithuania are often restricted to production of concrete floor for different purposes. Whereas, in other countries (USA, Japan, Germany and other) application area of fibre reinforcement is much wider, for example: bridge deck, thin-walled structures for special constructions (tunnels, reservoirs, etc), covering of roadway, airport landing strip, pipelines, pile foundation. Application of fibre reinforcement is considered as one of the most important development area of structural construction in the world.
Fibre reinforcement significantly improves service properties of concrete. Fibre reinforcement does not have considerable influence on concrete compressive strength, however it significantly changes fracture characteristics of tensile concrete. Fracture of non-reinforced tensile concrete is brittle, whereas with fibre reinforcement–plastic. This is due to restraining of tensile deformations by distributed fibres. Fibre reinforcement influence on concrete member is more effective than bar reinforcement, as tensile deformations are restrained in the whole volume of tensile zone. Whereas, tensile deformations in a RC member are restrained in the specific interaction area of reinforcement and concrete. Main advantages of fibre reinforcement are slow crack propagation, greater tensile and... [to full text]Jau kelis dešimtmečius plieno plaušas visame pasaulyje plačiai taikomas kaip priedas betono ir cementinio skiedinio mišiniams, naudojamiems statybinių konstrukcijų gamybai. Lietuvoje dispersinis armavimas dažniausiai naudojamas betonuojant įvairios paskirties pastatų grindis. Tuo tarpu, kitose pasaulio šalyse (JAV, Japonijoje, Vokietijoje ir kt.) dispersinė armatūra naudojama daug plačiau, pvz.: tiltų perdangoms, plonasienėms specialiųjų statinių (tunelių, rezervuarų ir t. t.) konstrukcijoms, kelių dangoms, oro uostų pakilimo takams, vamzdynams, poliniams pamatams ir t. t. Dispersinės armatūros taikymas visame pasaulyje laikoma viena iš prioritetinių statybinių konstrukcijų vystymosi sričių. Dispersinis armavimas neturi didesnės įtakos gniuždomajam betono stipriui, tačiau lemia visiškai skirtingą tempiamojo betono suirimo pobūdį. Nearmuoto tempiamojo betono suirimas yra trapus, tuo tarpu dispersiškai armuoto – plastinis. Tai lemia dispersiškai pasiskirsčiusio plaušo sukeliamas tempimo deformacijų suvaržymas. Dispersinio armavimo poveikis betoniniam elementui yra daug efektyvesnis nei strypinės armatūros, kadangi tempimo deformacijos varžomos visame tempiamosios zonos tūryje. Tuo tarpu klasikiniame gelžbetoniniame elemente tempimo deformacijos varžomos tik tam tikrame armatūros ir betono sąveikos plote. Lėtesnis plyšių vystymasis, didesnis atsparumas smūgiams ir nuovargiui bei plastiškumas yra pagrindiniai veiksniai, lemiantys dispersiškai armuotų gelžbetoninių konstrukcijų... [toliau žr. visą tekstą]
8
Kong, Kok Loon. "Cracking and tension zone behaviour in reinforced concrete flexural members." Thesis, University of Leeds, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427779.
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Sudoi, Elias K. "Factors influencing horizontal cracking in continuously reinforced concrete pavements (CRCP)." Thesis, University of North Texas, 2008. https://digital.library.unt.edu/ark:/67531/metadc9025/.
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This research presents the results on an experimental investigation to identify the significant factors influencing horizontal cracking in continuously reinforced concrete pavements (CRCP). An in-depth analysis of the microstructure, morphological characteristics of the interfacial transition zone (ITZ) and the observation of cracking using the environmental scanning electron microscope (ESEM) was done. Characterization of oxides using Fourier transform infrared spectroscopy (FTIR) and electron dispersive x-ray spectroscopy (EDS) was also performed. Water to cement ratio (w/c) and rebar temperature had a significant influence on the rebar-concrete bond strength. The 28-day shear strength measurements showed an increase in rebar-concrete bond strength as the water to cement ratio (w/c) was reduced from 0.50 to 0.40. There was a reduction in the peak pullout load as the temperature increased from 14oF to 252oF for the corroded and non-corroded rebar experiments. The corroded rebar pullout test results showed a 20-50 % reduction in bond strength compared to the non-corroded rebars. FTIR measurements indicated a presence of lepidocrocrite (γ -FeOOH) and maghemite (γ -Fe2O3) on the ITZ. ESEM images showed the existence of microcracks as early as three days after casting with the bridging of these cracks between coarse aggregate locations in the interfacial zone propagating through the mortar.
10
Farag, Hassan Mohamed. "The transient analysis and non linear behaviour of reinforced concrete elements." Thesis, University of Salford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308130.
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11
Vilanova, Marco Irene. "Bond-slip and cracking behaviour of glass fibre reinforced polymer reinforced concrete tensile members." Doctoral thesis, Universitat de Girona, 2015. http://hdl.handle.net/10803/328720.
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In this work, a methodology has been developed to implement the bond behaviour between concrete and GFRP bars in the numerical modelling. Based on experimental results and applying the inverse method, the bond law to be used in the numerical model is obtained.
The thesis continues with two experimental campaigns on GFRP RC elements under tensile sustained loads. The first experimental campaign consisted in testing GFRP RC elements with different target concrete strengths. The tests were carried out for a period between 35 a 39 days. Experimental results were compared with analytical codes for steel RC structures. The second experimental campaign consists on the analysis of bond of such structures under sustained load. The specimens were tested for a period between 90 and 130 days. Slip stabilization was observed to occur at 60 days after the beginning of the tests.En aquest treball s’ha desenvolupat una metodologia que permet la implementació del comportament adherent entre formigó i barres de material compost en la modelització numèrica. A partir de resultats experimentals i aplicant un mètode invers s’obtenen les lleis d’adherència aptes per ser incorporades a la modelització numèrica. Com a continuació de l’estudi s’han portat a terme dues campanyes experimentals en elements sotmesos a càrrega de tracció mantinguda. La primera campanya experimental va consistir en l’assaig de tirants de formigó variant la resistència del formigó. Els espècimens van estar sotmesos a càrrega mantinguda durant un període de 35-39 dies. Els resultats es van comparat amb models analítics existents per reforç estructural d’acer. En la segona campanya experimental es va aprofundir en l’estudi de l’adherència a llarg termini. Els espècimens van estar sotmesos a càrrega mantinguda durant un període de 90-130 dies observant una estabilització del lliscament 60 dies després de l’inici dels assaigs.
12
Chong, Kak Tien Civil & Environmental Engineering Faculty of Engineering UNSW. "Numerical modelling of time-dependent cracking and deformation of reinforced concrete structures." Awarded by:University of New South Wales. School of Civil & Environmental Engineering, 2004. http://handle.unsw.edu.au/1959.4/20634.
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For a structure to remain serviceable, crack widths must be small enough to be acceptable from an aesthetic point of view, small enough to avoid waterproofing problems and small enough to prevent the ingress of water that may lead to corrosion of the reinforcement. Crack control is therefore an important aspect of the design of reinforced concrete structures at the serviceability limit state. Despite its importance, code methods for crack control have been developed, in the main, from laboratory observations of the instantaneous behaviour of reinforced concrete members under load and fail to account adequately for the time-dependent development of cracking. In this study numerical models have been developed to investigate timedependent cracking of reinforced concrete structures. Two approaches were adopted to simulate cracking in reinforced concrete members. The first approach is the distributed cracking approach. In this approach, steel reinforcement is smeared through the concrete elements and bond-slip between steel and concrete is accounted for indirectly by including the tension stiffening effect. The second approach is the localized cracking approach, in which concrete fracture models are used in conjunction with bond-slip interface elements to model stress transfer between concrete and steel. Creep of concrete has been incorporated into the models by adopting the principle of superposition and the time-dependent development of shrinkage strain of concrete is modelled using an approximating function. Both creep and shrinkage were treated as inelastic pre-strains and applied to the discretized structure as equivalent nodal forces. Apart from material non-linearity, non-linearity arising from large deformation was also accounted for using the updated Lagrangian formulation. The numerical models were used to simulate a series of laboratory tests for verification purposes. The models were assessed critically by comparing the numerical results with the test data and the numerical results are shown to have good correlations with the test results. In addition, a comparison was undertaken among the numerical models and the pros and cons of each model were evaluated. A series of controlled parametric numerical experiments was devised and carried out using one of the numerical models. Various parameters were identified and investigated in the parametric study. The effects of the parameters were thoroughly examined and the interactions between the parameters were discussed in detail.
13
Cook, William Digby. "Studies of reinforced concrete regions near discontinuities." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75457.
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A non-linear finite element computer program capable of predicting the complete response of two-dimensional reinforced concrete members was developed. This tool which accounts for the stress strain characteristics of cracked concrete was used to predict the responses of a number of members containing discontinuities. These members included corbels, dapped end beams, beams with web holes, and deep beams. The results of tests performed by the author as well as tests performed by other researchers were compared with the non-linear predictions. In addition, simple strut and tie models suitable for designing regions near discontinuities were developed. The predictions obtained by these models were compared with the non-linear finite element predictions and with the test results.
14
Combrinck, Riaan. "Plastic shrinkage cracking in conventional and low volume fibre reinforced concrete." Thesis, Stellenbosch : University of Stellenbosch, 2011. http://hdl.handle.net/10019.1/6572.
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Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2011.ENGLISH ABSTRACT: Plastic shrinkage cracking (PSC) is the cracking caused by the early age shrinkage of concrete within the first few hours after the concrete has been cast. It results in unsightly surface cracks that serve as pathways whereby corroding agents can penetrate the concrete which shortens the expected service life of a structure. PSC is primarily a problem at large exposed concrete surfaces for example bridge decks and slabs placed in environmental conditions with high evaporation rates. Most precautionary measures for PSC are externally applied and aimed to reduce the water loss through evaporation. The addition of a low dosage of polymeric fibres to conventional concrete is an internal preventative measure which has been shown to reduce PSC. The mechanisms involved with PSC in conventional and low volume fibre reinforced concrete (LV-FRC) are however not clearly understood. This lack of knowledge and guidance leads to neglect and ineffective use of preventative measures. The objective of this study is to provide the fundamental understanding of the phenomena of PSC. To achieve the objective, an in depth background study and experiments were conducted on fresh conventional concrete and LV-FRC. The three essential mechanisms required for PSC are: 1→ Capillary pressure build-up between the particles of the concrete is the source of shrinkage. 2→ Air entry into a concrete initiates cracking. 3→ Restraint of the concrete is required for crack forming. The experiments showed the following significant findings for conventional and LV-FRC: PSC is only possible once all the bleeding water at the surface has evaporated and once air entry has occurred. The critical period where the majority of the PSC occurs is between the initial and final set of concrete. Any preventative measure for PSC is most effective during this period. The bleeding characteristics of a mix have a significant influence on PSC. Adding a low volume of polymeric fibres to concrete reduces PSC due to the added resistance that fibres give to crack widening, which increases significantly from the start of the critical period. The fundamental knowledge gained from this study can be utilized to develop a practical model for the design and prevention of PSC in conventional concrete and LV-FRC.
AFRIKAANSE OPSOMMING: Plastiese krimp krake (PSK) is die krake wat gevorm word a.g.v. die vroeë krimping van beton binne die eerste paar ure nadat die beton gegiet is. Dit veroorsaak onooglike oppervlak krake wat dien as kanale waardeur korrosie agente die beton kan binnedring om so die dienstydperk van die struktuur te verkort. Dit is hoofsaaklik ʼn probleem by groot blootgestelde beton oppervlaktes soos brug dekke en blaaie wat gegiet is in klimaat kondisies met hoë verdamping tempo’s. Meeste voorsorgmaatreëls vir PSK word ekstern aangewend en beperk die water verlies as gevolg van verdamping. Die byvoeging van ʼn lae volume polimeriese vesels is ʼn interne voorsorgmaatreël wat bekend is om PSK te verminder. Die meganismes betrokke ten opsigte van PSK in gewone beton en lae volume vesel versterkte beton (LV-VVB) is vaag. Die vaagheid en tekort aan riglyne lei tot nalatigheid en oneffektiewe aanwending van voorsorgmaatreëls. Die doel van die studie is om die fundamentele kennis oor die fenomeen van PSK te gee. Om die doel te bereik is ʼn indiepte agtergrond studie en eksperimente uitgevoer op gewone beton en LV-VVB. Die drie meganismes benodig vir PSK is: 1→ Kapillêre druk tussen die deeltjies van die beton is die hoof bron van krimping. 2→ Lugindringing in die beton wat krake inisieer. 3→ Inklemming van die beton is noodsaaklik vir kraakvorming. Die eksperimente het die volgende noemenswaardige bevindinge opgelewer: PSK is slegs moontlik indien al die bloeiwater van die beton oppervlakte verdamp het en indien lug die beton ingedring het. Die kritiese periode waar die meerderheid van die PSK plaasvind is tussen die aanvanklike en finale set van die beton. Enige voorsorgmaatreël vir PSK is mees effektief gedurende die periode. Die bloei eienskappe van ʼn meng het ʼn noemenswaardige effek op die PSK. Die byvoeging van ʼn lae volume polimeriese vesels tot beton verminder die PSK deur die addisionele weerstand wat die vesels bied teen die toename in kraakwydte. Die weerstand vergroot noemenswaardig vanaf die begin van die kritiese periode. Die fundamentele kennis wat in die studie opgedoen is, kan gebruik word vir die ontwikkeling van ʼn praktiese model vir die ontwerp en verhoed van PSK in gewone beton en LV-VVB.
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Combrinck, Riaan. "Plastic shrinkage cracking in conventional and low volume fibre reinforced concrete." Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/71648.
Full textAbstract:
Thesis (MScEng)--Stellenbosch University, 2012.ENGLISH ABSTRACT: Plastic shrinkage cracking (PSC) is the cracking caused by the early age shrinkage of concrete within the first few hours after the concrete has been cast. It results in unsightly surface cracks that serve as pathways whereby corroding agents can penetrate the concrete which shortens the expected service life of a structure. PSC is primarily a problem at large exposed concrete surfaces for example bridge decks and slabs placed in environmental conditions with high evaporation rates. Most precautionary measures for PSC are externally applied and aimed to reduce the water loss through evaporation. The addition of a low dosage of polymeric fibres to conventional concrete is an internal preventative measure which has been shown to reduce PSC. The mechanisms involved with PSC in conventional and low volume fibre reinforced concrete (LV-FRC) are however not clearly understood. This lack of knowledge and guidance leads to neglect and ineffective use of preventative measures. The objective of this study is to provide the fundamental understanding of the phenomena of PSC. To achieve the objective, an in depth background study and experiments were conducted on fresh conventional concrete and LV-FRC. The three essential mechanisms required for PSC are: 1→ Capillary pressure build-up between the particles of the concrete is the source of shrinkage. 2→ Air entry into a concrete initiates cracking. 3→ Restraint of the concrete is required for crack forming. The experiments showed the following significant findings for conventional and LV-FRC: PSC is only possible once all the bleeding water at the surface has evaporated and once air entry has occurred. The critical period where the majority of the PSC occurs is between the initial and final set of concrete. Any preventative measure for PSC is most effective during this period. The bleeding characteristics of a mix have a significant influence on PSC. Adding a low volume of polymeric fibres to concrete reduces PSC due to the added resistance that fibres give to crack widening, which increases significantly from the start of the critical period. The fundamental knowledge gained from this study can be utilized to develop a practical model for the design and prevention of PSC in conventional concrete and LV-FRC.
AFRIKAANSE OPSOMMING: Plastiese krimp krake (PSK) is die krake wat gevorm word a.g.v. die vroeë krimping van beton binne die eerste paar ure nadat die beton gegiet is. Dit veroorsaak onooglike oppervlak krake wat dien as kanale waardeur korrosie agente die beton kan binnedring om so die dienstydperk van die struktuur te verkort. Dit is hoofsaaklik ʼn probleem by groot blootgestelde beton oppervlaktes soos brug dekke en blaaie wat gegiet is in klimaat kondisies met hoë verdamping tempo’s. Meeste voorsorgmaatreëls vir PSK word ekstern aangewend en beperk die water verlies as gevolg van verdamping. Die byvoeging van ʼn lae volume polimeriese vesels is ʼn interne voorsorgmaatreël wat bekend is om PSK te verminder. Die meganismes betrokke ten opsigte van PSK in gewone beton en lae volume vesel versterkte beton (LV-VVB) is vaag. Die vaagheid en tekort aan riglyne lei tot nalatigheid en oneffektiewe aanwending van voorsorgmaatreëls. Die doel van die studie is om die fundamentele kennis oor die fenomeen van PSK te gee. Om die doel te bereik is ʼn indiepte agtergrond studie en eksperimente uitgevoer op gewone beton en LV-VVB. Die drie meganismes benodig vir PSK is: 1→ Kapillêre druk tussen die deeltjies van die beton is die hoof bron van krimping. 2→ Lugindringing in die beton wat krake inisieer. 3→ Inklemming van die beton is noodsaaklik vir kraakvorming. Die eksperimente het die volgende noemenswaardige bevindinge opgelewer: PSK is slegs moontlik indien al die bloeiwater van die beton oppervlakte verdamp het en indien lug die beton ingedring het. Die kritiese periode waar die meerderheid van die PSK plaasvind is tussen die aanvanklike en finale set van die beton. Enige voorsorgmaatreël vir PSK is mees effektief gedurende die periode. Die bloei eienskappe van ʼn meng het ʼn noemenswaardige effek op die PSK. Die byvoeging van ʼn lae volume polimeriese vesels tot beton verminder die PSK deur die addisionele weerstand wat die vesels bied teen die toename in kraakwydte. Die weerstand vergroot noemenswaardig vanaf die begin van die kritiese periode. Die fundamentele kennis wat in die studie opgedoen is, kan gebruik word vir die ontwikkeling van ʼn praktiese model vir die ontwerp en verhoed van PSK in gewone beton en LV-VVB.
16
Essili, Mohamed. "Control of Early Age Shrinkage Cracking in Reinforced Concrete Bridge Decks." University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1502447504502314.
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Liu, Youping. "Modeling the Time-to Corrosion Cracking of the Cover Concrete in Chloride Contaminated Reinforced Concrete Structures." Diss., Virginia Tech, 1996. http://hdl.handle.net/10919/30541.
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Significant factors on steel corrosion in chloride contaminated reinforced concrete and time-to-corrosion cracking were investigated in this study. Sixty specimens were designed with seven admixed chloride contents, three concrete cover depths, two reinforcing steel bar diameters, two exposure conditions, and a typical concrete with water to cement ratio of 0.45. Corrosion current density (corrosion rate), corrosion potential, ohmic resistance of concrete and temperature were measured monthly on these specimens using both the 3LP and Gecor devices. Metal loss measurements were performed in accordance with ASTM G1-90, method C3.5, after specimens cracked. The actual corrosion weight loss of the steel reinforcing bars was then compared to the result obtained from the corrosion rate measurement devices. An interaction model for characterizing the dynamic corrosion process was developed based on the five-year corrosion database. The model demonstrates that the corrosion rate is a function of chloride content, temperature at reinforcement depth, ohmic resistance of concrete, and corrosion time after initiation. A time-to-corrosion cracking model was suggested based on a corrosion-cracking conceptual model and critical mass of corrosion products. The model predicted times to corrosion cracking are in good agreement with the observed times to corrosion cracking of the cover concrete.Ph. D.
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賀小崗 and Xiaogang He. "Constitutive modeling of reinforced concrete for nonlinear finite element analysis." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1999. http://hub.hku.hk/bib/B31240264.
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Lam, W.-K. F. "Constitutive relations for finite element analysis of tension stiffening in reinforced concrete." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233266.
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Sabrah, Tamer Berry A. "Cracking behaviour of GFRP-reinforced concrete panels under uniaxial and biaxial tension /." Internet access available to MUN users only. Search for this title in:, 2009.
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Tian, Xiaoping. "Modeling reinforced concrete cracking due to corrosion with a fracture mechanics approach." Thesis, University of Ottawa (Canada), 2006. http://hdl.handle.net/10393/27300.
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With the increasing need of developing service life models for corrosion-induced damage in reinforced concrete structures, there has been a movement to model the concrete cover as a thick-wall cylinder subjected to an internal pressure due to corrosion products accumulation on the reinforcing steel. These models allow determining the amount of corrosion product necessary to initiate and propagate cracks along the cover. The first generation of models assume that concrete behaves linearly elastic and that the concrete cover does not have any residual tensile capacity once the tensile strength of the concrete has been reached. More advanced models include the softening behaviour of concrete beyond cracking initiation. This thesis proposes such a model wherein the state stress of the concrete cover due to accumulation of corrosion products is determined by analyzing an equivalent thick-wall cylinder subjected to a uniform internal pressure. Concrete is assumed to be an isotropic material, and deformations due to Poisson's ratio are ignored. To describe the behaviour of concrete in the softening region, a linear relation of stress versus displacement and a constant strain field are assumed. Mathematical expressions that determine the state of stress due to corrosion build-up at any point in the concrete cover are obtained by integrating the softening equations along the concrete cover. Analytical models for cracking initiation as well as longitudinal cracking of the concrete cover are formulated for both unconfined and confined conditions. The latter are the result of the presence of shear stirrups or tie/spiral reinforcement. To determine the validity of these models, their results are compared to published experimental data and finite element analyses. Finally, a parameterc analysis using the models is carried out in order to establish the role of significant model parameters on the resulting state of stress of the concrete cover and the associated damage.
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Busba, Ezeddin Rafaa. "Effect of Localized Corrosion of Steel on Chloride-Induced Concrete Cover Cracking in Reinforced Concrete Structures." Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4872.
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Abstract: Concrete cover cracking due to reinforcement corrosion is widely accepted as a limit-state indicator in defining the end of functional service life for existing reinforced concrete (RC) structures undergoing corrosion. Many of the currently available durability prediction models are incapable of providing realistic estimates of remaining service lives of RC structures beyond the corrosion initiation point. Therefore, the need to incorporate the length of the corrosion propagation stage in a comprehensive durability prediction approach has recently received much research attention. Previous research focus however was mostly limited to the case of uniformly corroding reinforcement with only few studies addressing the commonly encountered case of localized rebar corrosion. It was empirically shown in a previous study that localized corrosion can have a mitigating effect on time to concrete cover cracking due to the larger required depth of rebar corrosion penetration (Critical penetration or Xcrit). The present research was focused on developing a model for predicting Xcrit for various degrees of corrosion localization including new cases of highly localized corrosion. Accelerated corrosion testing of controlled anodic regions along axial rebars in sound concrete cylinders suggested that localized corrosion can increase Xcrit by up to about a factor of 10. The effect of corrosion localization on the orientation of corrosion-induced surface cracks was also addressed. Testing of freely corroding pre-cracked RC pipe specimens in a chloride-containing environment indicated that steel corrosion can be localized at intersection regions with the pre-existing cracks and uniformly distributed around the reinforcing steel perimeter. Numerical modeling was undertaken to substantiate the experimentally observed trends on a theoretical basis for various degrees of corrosion localization. A mechanical model was developed to improve understanding of the underlying mechanism responsible for corrosion-induced stresses. A thick-walled multiple-cylinder approach was employed to simulate crack initiation and propagation to account for the residual strength property of concrete after cracking by applying the principles of applied elasticity. For a given concrete cover depth, the amount of Xcrit was shown by modeling to be largely determined by the length of corroding region and the capacity of the induced cracks to accommodate produced rusts. The properties of both concrete-rebar interface and corrosion products were also found to have a significant impact on Xcrit. Based on the model and experimental trends and comparisons with literature data, an improved relationship for the estimation of Xcrit was proposed. An electrochemical model was also formulated to address the possible role of corrosion aggravation due to macrocell coupling in counteracting the mitigating effect of increased Xcrit on time to concrete cover cracking. Findings confirmed that corrosion localization can reasonably be considered a mitigating factor for extending the corrosion propagation stage, and provided more precise quantification to that effect.
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Arne, Kevin C. "Crack depth measurement in reinforced concrete using ultrasonic techniques." Thesis, Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51914.
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Concrete is the most widely used construction material in the world, so the assessment of damage in concrete is critical from the point of view of both safety and cost. Of particular interest are macro cracks that extend through the concrete cover of the reinforcement, which can potentially expose the reinforcement to corrosive elements. The high density of scatterers such as aggregate and voids in concrete makes quantitative imaging with coherent ultrasound difficult. As an alternative, this research focuses on diffuse energy based ultrasonic methods rather than coherent ultrasonic methods for crack depth assessment. Two types of ultrasonic measurements were made on real cracks formed under four point bending: one that focuses on time of flight measurements from an impactor; while the other uses the arrival time of maximum energy in a diffuse field excited by an impulsive load from a transducer. Each of these ultrasonic techniques is used to interrogate a macro crack in a concrete beam, and the results are compared to determine their accuracy and robustness. The actual crack depth is determined using direct surface measurements and a destructive dye-injected approach with drilled cores. The results suggest that the diffusion method, using a maximum energy approach, more accurately estimates the crack than visual inspection and impact echo methods, which overestimate the depth.
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Newhouse, Charles D. "Corrosion rates and the time to cracking of chloride contaminated reinforced concrete bridge components." Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-06162009-063230/.
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Hossain, Tahsin Reza. "Numerical modelling of deflections of reinforced concrete flat slabs under service loads." Thesis, Imperial College London, 1999. http://hdl.handle.net/10044/1/7243.
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Wu, Yi, and 吳奕. "Post-crack and post-peak behavior of reinforced concrete members by nonlinear finite element analysis." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B37006447.
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Van, der Westhuizen Daniel Erasmus. "Using synthetic fibres in concrete to control drying shrinkage cracking in concrete slabs-on-grade." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/85696.
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Thesis (MScEng)-- Stellenbosch University, 2013.ENGLISH ABSTRACT: Macro synthetic fibre reinforced concrete (SynFRC) is a relatively new concrete for the purpose of being used in structural elements which only require minimum reinforcement and are supported continuously by sub-layers. One structural element that is of particular interest is slabs-on-grade which is supported by a subgrade/sub-base and requires minimum reinforcement to control the shrinkage strains which may result in cracking. The aim of this project is to investigate the potential use of macro SynFRC in the application of controlling drying shrinkage cracking (DSC) in concrete slabs-on-grade. The focus is on the use of concrete slabs-on-grade that is intended for industrial floors. The SynFRC material parameters of interest were characterised first with the aid of various experimental tests. These are: flexural tests, compression tests, friction tests between the SynFRC and wooden surfaces used for full scale testing, and the shrinkage of the concrete. Next the post-cracking tensile behaviour of the SynFRC was determined by way of an inverse analysis. These tensile responses were subsequently used to perform a series of different finite element analyses. These analyses were performed on specific slabs-on-grade to determine the effects of the added tensile behaviour of the SynFRC on the DSC. The results obtained concerned: the spacing of cracks, the maximum and average crack width, and the difference in crack width between the normal concrete (NC) and the SynFRC. These changes take place in accordance to the concrete age. From the analyses it was determined that the addition of fibres gives the concrete a ductility that allows the concrete to crack more than NC, yet does not allow the cracks to propagate. This applies to low fibre contents of less than 0.4% by volume and a slab thickness of 200mm, as well as to fibre contents that have Re,3 values of 0.51 and higher. Moreover, it results in improvements seen when adding fibres if the friction is sticky, meaning when the maximum friction between the slab and the subgrade is reached with a very small amount of movement. With a stickier friction though smaller crack widths occur within both the NC and the SynFRC.
AFRIKAANSE OPSOMMING: Makro sintetiese vesel versterkte beton (SynFRC) is 'n relatiewe nuwe beton. Dit het ten doel om gebruik te word in strukturele elemente wat minimale versterking benodig en wat deurlopend deur sublae ondersteun word. Een spesifieke strukturele element van belang is grondvloere wat deur 'n sublaag ondersteun word en wat minimale ondersteuning benodig om die krimping vervorming te beheer wat moontlike krake kan veroorsaak. Die doel van die projek was om die potensiële gebruik van makro sintetiese vesels te ondersoek tydens die beheer van die uitdroog krimp kraking van 'n beton grondvloer. Die fokus was op die gebruik van betonvloere vir fabrieksdoeleindes. Die eienskappe van SynFRC materiale is vooraf vasgestel vir die doel van verskeie eksperimentele toetse. Hierdie toetse sluit in buigbaarheidstoetse, druktoetse, krimping van beton en toets van wrywing tussen die SynFRC en hout oppervlaktes wat gebruik is vir volskaalse toets. Die trek gedrag van SynFRC na kraking is vasgestel deur inverse analise. Hierdie trek gedrag is dan gebruik om 'n reeks eindige element analises uit te voer. Hierdie analises is uitgevoer op spesifieke grondvloere om die effek te bepaal van verhoogde trek gedrag van SynFRC op die uitdroog krimp kraking. Volgens die uitslae sodoende verkry was die kraakspasiëring, die maksimum en gemiddelde kraakwydte en die verskil in die kraakwydte tussen normale beton en die SynFRC as ‘n funksie van beton oudedom. Vanuit die analises het dit duidelik geblyk dat die byvoeging van vesels die beton se smeebaarheid verhoog het en dit het tot gevolg gehad dat die beton meer krake vorm, maar dat die krake nie vergroot nie. Dit is waargeneem by 'n lae vesel inhoud van minder as 0.4% per volume en 'n betonblad met 'n dikte van 200mm. Dit is ook waargeneem by 'n hoër vesel volume wat Re,3 waardes van 0.51 en hoër het. Kleiner kraakwydte is waargeneem waar vesel volume verhoog is indien die wrywing hoër is, bedoelende dat die maksimum wrywing tussen die betonblad en die sublaag bereik is met baie min beweging. Daar het wel kleiner kraakwydtes in beide die normale beton en die SynFRC voorgekom waar daar hoër wrywing was.
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Nieuwoudt, Pieter Daniel. "Quantifying the cracking behaviour of strain hardening cement-based composites." Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/20076.
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Thesis (MScEng)--Stellenbosch University, 2012.ENGLISH ABSTRACT: Strain Hardening Cement Based Composite (SHCC) is a type of High Performance Fibre Reinforced Cement-based Composite (HPFRCC). SHCC contains randomly distributed short fibres which improve the ductility of the material and can resist the full tensile load at strains up to 5 %. When SHCC is subjected to tensile loading, fine multiple cracking occurs that portrays a pseudo strain hardening effect as a result. The multiple cracking is what sets SHCC aside from conventional Reinforced Concrete (RC). Conventional RC forms one large crack that results in durability problems. The multiple cracks of SHCC typically have an average crack width of less than 80 μm (Adendorff, 2009), resulting in an improved durability compared to conventional RC. The aim of this research project is to quantify the cracking behaviour of SHCC which can be used to quantify the durability of SHCC. The cracking behaviour is described using a statistical distribution model, which represents the crack widths distribution and a mathematical expression that describes the crack pattern. The cracking behaviour was determined by measuring the cracks during quasi-static uni-axial tensile tests. The cracking data was collected with the aid of a non-contact surface strain measuring system, namely the ARAMIS system. An investigation was performed on the crack measuring setup (ARAMIS) to define a crack definition that was used during the determination of the cracking behaviour of SHCC. Several different statistical distributions were considered to describe the distribution of the crack widths of SHCC. A mathematical expression named the Crack Proximity Index (CPI) which represents the distances of the cracks to each other was used to describe the crack pattern of SHCC. The Gamma distribution was found to best represent the crack widths of SHCC. It was observed that different crack patterns can be found at the same tensile strain and that the CPI would differ even though the same crack width distribution was found. A statistical distribution model was therefore found to describe the CPI distribution of SHCC at different tensile strains and it was established that the Log-normal distribution best describes the CPI distribution of SHCC. After the cracking behaviour of SHCC was determined for quasi-static tensile loading, an investigation was performed to compare it to the cracking behaviour under flexural loading. A difference in the crack widths, number of cracks and crack pattern was found between bending and tension. Therefore it was concluded that the cracking behaviour for SHCC is different under flexural loading than in tension.
AFRIKAANSE OPSOMMING: “Strain Hardening Cement-based Composite” (SHCC) is ‘n tipe “High Performance Fibre Reinforced Cement-based Composite” (HPFRCC). SHCC bevat kort vesels wat ewekansig verspreid is, wat die duktiliteit van die material verbeter en dit kan die maksimum trekkrag weerstaan tot en met ‘n vervorming van 5 %. Wanneer SHCC belas word met ‘n trekkrag, vorm verskeie fyn krake wat ‘n sogenaamde vervormingsverharding voorstel. Die verskeie krake onderskei SHCC van normale bewapende beton. Normale bewapende beton vorm een groot kraak met die gevolg dat duursaamheidsprobleme ontstaan. Die gemiddelde kraakwydte van SHCC is minder as 80 μm (Adendorff, 2009) en het dus ‘n beter duursaamheid as normale bewapende beton. Die doel van die navorsingsprojek is om die kraak gedrag van SHCC te kwantifiseer en wat dan gebruik kan word om die duursaamheid van SHCC te kwantifiseer. Die kraak gedrag is beskryf deur ‘n statistiese verspreiding model wat die kraak wydtes se verspreiding voorstel en ‘n wiskundige uitdrukking wat die kraak patroon beskryf. Die kraak gedrag was bepaal deur die krake te meet tydens die semi-statiese een-asige trek toetse. Die kraak data was met behulp van ‘n optiese vervormings toestel, naamlik die ARAMIS, versamel. ‘n Ondersoek is gedoen op die kraak meetings opstelling (ARAMIS), om ‘n kraak definisie te definieer wat gebruik is om die kraak gedrag te bepaal. Daar is gekyk na verskeie statistiese verdelings om die kraak wydtes van SHCC te beskryf. Die kraak patroon van SHCC is beskryf met ‘n wiskundige uitdrukking genoem die “Crack Proximity Index” (CPI) wat die krake se afstande van mekaar voorstel. Dit is bevind dat die Gamma verdeling die kraak wydtes van SHCC die beste beskryf. Daar is waargeneem dat verskillende kraak patrone by dieselfde vervorming verkry kan word en dat die CPI kan verskil al is die kraak wydte verdeling dieselfde. ‘n Statistiese verdelingsmodel is dus gevind om die CPI verdeling van SHCC te beskryf by verskillende vervormings, en daar is vasgestel dat die Log-normaal verdeling die CPI verdeling van SHCC die beste beskryf. Nadat die kraak gedrag van SHCC bepaal is vir semi-statiese trek-belasting, is ‘n ondersoek gedoen waar die trek-kraak gedrag vergelyk is met buig-kraak gedrag. ‘n Verskil in die kraak wydtes, aantal krake en kraak patroon is gevind tussen buiging en trek. Dus is die gevolgtrekking gemaak dat die kraak gedrag van SHCC verskillend is in buiging as in trek.
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Giaccio, Craig 1974. "Flange effectiveness in the resistance of shear on RC T-beams subjected to point loads." Monash University, Dept. of Civil Engineering, 2003. http://arrow.monash.edu.au/hdl/1959.1/5708.
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Maritz, Jaco-Louis. "An investigation into the use of low volume - fibre reinforced concrete for controlling plastic shrinkage cracking." Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/19983.
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Thesis (MScEng)--Stellenbosch University, 2012.ENGLISH ABSTRACT: Plastic shrinkage cracking (PSC) in concrete is a well-known problem and usually occurs within the first few hours after the concrete has been cast. It is caused by a rapid loss of water from the concrete, either from the surface through evaporation or through absorption by dry subgrade or formwork in contact with the concrete and results in an overall reduction in concrete volume. If this volume reduction or shrinkage is restrained, plastic shrinkage cracks can occur. Plastic shrinkage cracks create an unsightly appearance on the concrete surface which reduces the quality of the concrete structure. These cracks also develop weak points in the concrete which can be widened and deepened later on by drying shrinkage and thermal movement. As a result harmful substances may enter the cracks causing accelerated concrete deterioration. These cracks may also expose the steel reinforcement causing it to corrode more aggressively. Consequently, the aesthetic value, serviceability, durability and overall performance of the concrete will be reduced. Therefore it is important to consider methods of limiting PSC. One of these methods is the addition of low volumes of polymeric fibres to concrete to reduce PSC. However, the application of this low volume fibre reinforced concrete (LV-FRC) is not clearly understood since there is a lack of knowledge and guidance available for the use of LV-FRC. The objective of this study is to gain a full understanding of PSC behaviour in conventional concrete and LV-FRC by investigating the effects of evaporation and bleeding as well as the effect of various fibre properties on PSC. The following significant findings were attained: A basis for a crack prediction model in conventional concrete was developed using the average differences in cumulative evaporation and cumulative bleeding to create a crack prediction value (CPV). This preliminary model showed that there exists a certain CPV range (-0.2 to 0.4 kg/m2 for this study) where a slight decrease in the CPV results in a significant PSC reduction. It also showed that if the CPV falls outside this range, varying the bleeding or evaporation conditions will have very little effect on the PSC. A study on the fibre properties in LV-FRC showed that there exist certain limits to the fibre volume, length and diameter where a further increase or decrease in value will have no or little effect on reducing PSC. It also showed that the effect of the fibres depend on the level of severity of PSC. The knowledge gained from this investigation can serve as a basis for the design of a model that can predict the risk of PSC in conventional concrete and specify preventative measures needed to reduce this risk. It also provides information that can be used to develop guidelines for the effective use of LV-FRC.
AFRIKAANSE OPSOMMING: Plastiese krimp krake (PKK) in beton is `n bekende probleem en vorm gewoonlik binne die eerste paar uur nadat die beton gegiet is. Dit word veroorsaak deur die vinnige waterverlies vanuit die beton, óf deur verdamping vanaf die beton oppervalk óf deur absorpsie van `n droeë grondlaag of bekisting wat in kontak is met die beton. Dit veroorsaak `n algehele vermindering in beton volume. As hierdie krimping van die beton beperk word, kan plastiese krimp krake ontstaan. PKK skep 'n onooglike voorkoms van die beton oppervlakte en verlaag die kwaliteit van die beton struktuur. Hierdie krake tree ook op as swak plekke in die beton wat later kan verbreed of verdiep deur droogkrimping en termiese beweging. Gevolglik kan skadelike stowwe vanuit die omgewing die krake binnedring wat lei tot versnelde agteruitgang van die beton. Hierdie krake kan ook die staalbewapening ontbloot wat veroorsaak dat dit vinniger roes. Gevolglik verminder die estetiese waarde, diensbaarheid, duursaamheid en algehele prestasie van die beton. Daarom is dit belangrik om metodes te ondersoek vir die beperking van PKK. Een van hierdie metodes is die byvoeging van lae volumes polimeer vesels tot beton om PKK te verminder. Die toepassing van hierdie lae volume - vesel versterkte beton (LV-VVB) word egter nog nie volledig verstaan nie as gevolg van 'n algemene gebrek aan kennis en riglyne vir die gebruik van die LV-VVB. Die doel van hierdie studie is om 'n volledige begrip van PKK gedrag in normale beton asook LV-VVB te kry. Dit word behaal deur die effek van verdamping en bloei op PKK sowel as die effek van verskillende vesel eienskappe op PKK te ondersoek. Die volgende noemenswaardige bevindinge is bekry. • Die basis van 'n kraak voorspellingsmodel vir gewone beton is ontwikkel deur gebruik te maak van die gemiddelde verskil tussen die kumulatiewe verdamping en die kumulatiewe bloei om 'n kraak voorspellingswaarde (KVW) te vorm. Hierdie voorlopige model toon dat daar `n sekere KVW interval ontstaan (-0,2 tot 0,4 kg/m2 vir hierdie studie) waar slegs 'n effense vermindering in die KVW 'n geweldige vermindering in die PKK tot gevolg het. Dit dui ook aan dat, indien die KVW buite hierdie interval val, ʼn verandering in die bloei of verdamping toestande `n baie klein invloed op die PKK het. 'n Studie oor die vesel eienskappe in LV-VVB het gewys dat daar sekere grense is aan die vesel volume, lengte en deursnee waardes, waar 'n verdere toename of afname in waarde min of geen effek het op die vermindering van PKK nie. Dit wys ook dat die effek van die vesels grotendeels afhanklik is van die risiko vlak vir PKK. Die kennis wat uit hierdie ondersoek opgedoen is, kan dien as 'n basis vir die ontwerp van 'n model wat die risiko van PKK in gewone beton kan voorspel en daarvolgens besluit op 'n voorkomingsmaatsreël om hierdie risiko te verminder. Dit bied ook inligting wat gebruik kan word om riglyne te ontwikkel vir die effektiewe gebruik van LV-VVB.
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Soranakom, Chote, and Barzin Mobasher. "Flexural Analysis and Design of Textile Reinforced Concrete." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1244046537373-61938.
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A model is presented to use normalized multi-linear tension and compression material characteristics of strain-hardening textile reinforced concrete and derive closed form expressions for predicting moment-curvature capacity. A set of design equations are derived and simplified for use in spreadsheet based applications. The model is applicable for both strain-softening and strainhardening materials. The predictability of the simplified model is checked by model calibration and development of design charts for moment capacity and stress developed throughout the cross section of a flexural member. Model is calibrated by predicting the results of Alkali Resistant Glass and Polyethylene fabrics. A case for the flexural design of Glass Fiber Reinforced Concrete (GFRC) specimen as a simply supported beam subjected to distributed load is used to demonstrate the design procedure.
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Barbiero, Marialuisa. "Cover cracking of concrete slabs induced by rebar corrosion." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
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The phenomenon of concrete cracking due to corrosion of embedded reinforcement steel bars in concrete has been investigated for years. As a consequence of the steel corrosion that is accelerated by cold climates, sea water, spray and from chloride-based acceleration agents, internal cracks form. These agents originate a slow propagation of corrosion products around the embedded steel, forming a passive film, which can be elementary understood as a radial force present all around the steel, creating compressive stresses in concrete. This pressure causes the formation of microcracks that permit the passive film to infill in the structure and propagate. A finite element analysis will be carried out, in order to study the relationship of reinforced concrete features. These are the bar diameter, space between the rebars, concrete strength and the cover thickness. In order to simulate and describe the behaviour of the concrete, the Concrete Damaged Plasticity – CDP, is used. The elastic is easily described by the elastic modulus and the Poisson’s ratio, while the non-linear is more complex. The CDP method considers both compression and tension strengths, gaining as output the cracking pattern. The simulation proposed consists by the modelling of a two-dimensional model, in which the reinforced steel bars will be inserted as holes in the geometric features. The model features internal boundary conditions placed on each side of the rebars/holes. At the end, four groups of simulations are proposed, in which various combinations of the parameters considered, are provided. These corresponds of four different concrete strengths, three different diameters of the steel rebars, five different cover thicknesses and four different spacings between the rebars. The simulations show the probable cracking paths, based on the internal displacement given by the pressure formed by the corrosion products.
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Bliuc, Radu Aerospace Civil & Mechanical Engineering Australian Defence Force Academy UNSW. "Particularities of the structural behaviour of reinforced high strength concrete slabs." Awarded by:University of New South Wales - Australian Defence Force Academy. School of Aerospace, Civil and Mechanical Engineering, 2004. http://handle.unsw.edu.au/1959.4/38749.
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The introduction of high strength concrete in construction demanded an assessment of the current methods of structural design. In the case of the slabs, the benefits brought about by concretes of higher strength could translate into design of slender sections. Theoretically these sections could be prone to excessive deflections. The flexural behaviour of such structural elements should be carefully assessed. The present thesis addresses a series of particular issues such as deflection at service loads, crack formation and development of tension stiffening and ductility. An experimental program on large-scale samples was conducted. Six one way and four two way slabs made of reinforced high strength concrete were tested under simulated and accurately measured equally distributed loads. Different loading stages were recorded. Crack formation, crack patterns and yield line disposition were observed. The main characteristics of concrete that influence the deflection behaviour were assessed based on collected data and on available literature results. Statistical methods were employed in order to refine empirical equations that help in the design of slabs. To improve the calculation of deflection of slabs a new equation for the effective moment of inertia was proposed. The new formula was integrated into a method of calculating deflection and verified against experimental results. Limits of the use of high strength concrete in slabs were investigated by means of a parametric study. This was designed to answer some questions as: which would be the most important characteristics of high-strength concrete that influence the design and up to what value of strength would the beneficial effect on deflection exhaust its effectiveness. Models based on the refined empirical equations for different concrete parameters were proposed. Another area that has been studied was the ductility of high strength concrete slabs. An analytical comparative study of the ductility of slabs reinforced with steel of different ductility class was conducted. Results were critically appraised and discussed.
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Carlswärd, Jonas. "Shrinkage cracking of steel fibre reinforced self compacting concrete overlays : test methods and theoretical modelling /." Luleå : Division of Structural Engineering, Luleå University of Technology, 2006. http://epubl.ltu.se/1402-1544/2006/55/LTU-DT-0655-SE.pdf.
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Gribniak, Viktor. "Shrinkage Influence on Tension-Stiffening of Concrete Structures." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2009. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2009~D_20091102_090235-06535.
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Due to the use of refined ultimate state theories as well as high strength concrete and reinforcement, resulting in longer spans and smaller depths, the serviceability criteria often limits application of modern reinforced concrete (RC) superstructures. In structural analysis, civil engineers can choose between traditional design code methods and numerical techniques. In order to choose a particular calculation method, engineers should be aware of accuracy of differ-ent techniques. Adequate modelling of RC cracking and, particularly, post-cracking behaviour, as one of the major sources of nonlinearity, is the most im-portant and difficult task of deformational analysis. In smeared crack approach dealing with average cracking and strains, post-cracking effects can be modelled by a stress-strain tension-stiffening relationship. Most known tension-stiffening relationships have been derived from test data of shrunk tension or shear mem-bers. Subsequently, these constitutive laws were applied for modelling of bend-ing elements which behaviour differs from test members. Furthermore, such re-lationships were coupled with shrinkage effect. Therefore, present research aims at developing a technique for deriving a free-of-shrinkage tension-stiffening re-lationship using test data of shrunk bending RC members. The main objective of this PhD dissertation is to investigate shrinkage influence on deformations and tension-stiffening of RC members subjected to short-term loading.
Present... [to full text]Pastaraisiais metais vis plačiau taikant stiprųjį betoną bei armatūrą, konst-rukcijų perdengiamos angos didėja, o skerspjūviai mažėja. Todėl projektuojant standumo (įlinkių) sąlyga vis dažniau tampa lemiamu veiksniu. Inžinieriai gelž-betoninių konstrukcijų apskaičiavimams gali taikyti empirinius normų arba skai-tinius metodus. Vieno ar kito skaičiavimo metodo parinkimas turi būti pagrįstas statistiniais tikslumo analizės rezultatais. Yra žinoma, kad adekvatus gelžbetoninio elemento pleišėjimo (ypač plyšių vystymosi stadijos) modeliavimas yra vienas sudėtingiausių netiesinės mechani-kos uždavinių. Toks uždavinys gali būti išspręstas taikant vidutinių plyšių kon-cepciją, kai pleišėjimo proceso modeliavimui naudojama tempiamojo betono vidutinių įtempių ir deformacijų diagrama. Dauguma tokių diagramų gautos, naudojant tempimo arba šlyties bandymo rezultatus. Pabrėžtina, kad šių diagra-mų taikymas lenkiamųjų gelžbetoninių elementų modeliavime duoda nemažas paklaidas. Kitas svarbus aspektas yra tai, kad gelžbetoniniuose bandiniuose, iki juos apkraunant trumpalaike apkrova, vyksta betono susitraukimas. Šiame darbe buvo siekiama sukurti metodą, leidžiantį pagal eksperimentinius lenkiamųjų gelžbetoninių elementų duomenis gauti tempiamojo betono vidutinių įtempių ir deformacijų diagramas, įvertinant betono susitraukimo įtaką. Pagrindinis diser-tacijos tikslas yra įvertinti ikieksploatacinių betono susitraukimo ir valkšnumo poveikį gelžbetoninių elementų, apkrautų trumpalaike apkrova... [toliau žr. visą tekstą]
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Gerber, Johan Andries Kritzinger. "Characterization of cracks on ultra thin continuously reinforced concrete pavements." Thesis, Stellenbosch : University of Stellenbosch, 2011. http://hdl.handle.net/10019.1/6772.
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Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2011.ENGLISH ABSTRACT: The southbound screener lane of the Heidelberg Traffic Control Centre received structural improvements by means of an ultra thin continuously reinforced concrete pavement (UTCRCP) overlay. This experimental overlay forms part of the South African National Roads Agency Limited’s innovative highway repair strategy on existing pavements that have exceeded design life. The primary objective of this study was to characterize the UTCRCP overlay with regard to crack spacing formation under accelerated pavement testing (APT). Characterization comprised of empirical modelling techniques, statistical analysis, non destructive testing and software simulations. Pavement deflection responses were empirically and linear elastically converted to input parameters. These parameters were used in the mean crack spacing prediction model of the Mechanistic-Empirical Pavement Design Guide (M-E PDG). Observed cracking under APT was recorded and analyzed by means of descriptive statistics. The outcome of the M-E PDG’s mean crack spacing and the statistics of the observed cracking were evaluated against cncPave simulations. Initial shrinkage crack formations ranged from 500 mm to 900 mm, with a mean spacing of 695 mm. Subsequent secondary cracking reduced the segments, delineated by initial cracking, to intervals consisting of 100 mm to 350 mm. A statistical analysis of the observed cracking indicated that traffic had little effect on the transverse crack spacing formation. The observed cracks yielded a mean spacing of 296 mm, compared to the 186 mm of the M-E PDG mean crack spacing calculation. cncPave simulations indicated that the expected range of cracking would fall between 237 mm and 350 mm with a probability of 50% that crack spacing would exceed 265 mm. The 50th percentile of the observed cracks resulted in a spacing of 233 mm. The APT project was limited to a single test section. No pavement failures occurred during the APT project. A total of 2.8 million 80 kN load repetitions were applied to the UTCRCP. However circular crack formations regarded as a punchout development have formed on the UTCRCP test section. Circular cracks formed around weaknesses in the pavement system. The prediction of these punchout formations incorporates the mean crack spacing result. Occurrence of mean crack spacing forms part of a crack spacing distribution defined by a range. Therefore designing a punchout prediction model for UTCRCP should include the characteristics and range of the crack pattern and not merely the mean crack spacing value. Key Words: UTCRCP, APT, Mean Crack Spacing, Punchout, Descriptive Statistics, cncPave, M-E PDG, Transverse Cracks, Dense Liquid Foundation, Elastic Solid Foundation.
AFRIKAANSE OPSOMMING: Die suidwaartse moniteerings laan van die Heidelberg Verkeersbeheer Sentrum, het strukturele verbetering ondergaan deur die konstruksie van ‘n ultradun aaneen-gewapende betonplaveisel (UDAGBP) wat dien as ‘n deklaag. Hierdie eksperimentele deklaag is deel van die Suid-Afrikaanse Nasionale Paaie Aggentskap Beperk (SANRAL) se vernuftige deurpadherstelstrategie vir bestaande deurpaaie waarvan die ontwerplewe verstryk het. Die primêre doel van hierdie studie is om die UDAGBP te karakteriseer, met betrekking tot kraakspasiëring, deur middel van Versnelde Plaveisel Toetsing (VPT). Die karakteriseringsproses het bestaan uit empiriese moduleringstegnieke, statistiese ontleding, nie-destruktiewe toetsmetodologieë en sagtewaresimulasies. Die plaveiseldefleksiegedrag is empiries en linieêr elasties ontleed en omgeskakel na invoerparameters. Hierdie parameters is gebruik in die peilingsmodel vir gemiddelde kraakspasiëring van die Meganisties-Empiries Plaveisel Ontwerpsgids (M-E POG). Waargenome kraakspasiëring na die afloop van VPT is opgeteken en deur middel van beskrywende statistiek ontleed. Die resultate van die M-E POG se gemiddelde kraakspasiëring en die statistiese ontleding van die waargenome krake is geëvalueer teenoor cncPave simulasies. Aanvanklike krimpingskrake het gevorm met wisselende kraakspasiëring tussen 500 mm en 900 mm met ‘n gemiddelde spasiëring van 695 mm. Daaropvolgende krake het die aanvanklike segmente, wat gevorm het tydens die aanvanklike krimpingskrake, verkort na intervalle van 100 mm tot 350 mm. ‘n Statistiese ontleding van die waargeneemde krake het aangedui dat verkeer weinig ‘n aandeel het in die dwarskraak-vormingsproses. Die waargenome krake het ‘n gemiddelde spasiëring van 296 mm in vergelyking met 186 mm van die M-E POG se gemiddelde kraakspasiëring berekening. cncPave simulasies het aangedui dat die verwagte kraakspasiëringsgrense tussen 237 mm en 350 mm is en ‘n 50% waarskynlikheid dat die kraakspasiëring meer as 265 mm is. Die VPT projek is beperk tot ‘n enkele toetsseksie. Geen plaveiselfalings is waargeneem gedurende die VPT projek nie. In totaal was 2.8 miljoen as-lasherhalings aangewend op die UDAGBP. Daar het egeter sirkelvormige kraakformasies, wat beskou word as ponsswigting, ontwikkel op die UDAGBP toetsseksie. Sirkelvormige kraakpatrone het gevorm rondom swak plekke in die plaveisel. Die peilingsmodelle van hierdie ponsswigting maak gebruik van die gimiddelde kraakspasiëringsresultaat. Die verskynsel van gemiddelde kraakspasiëring in hierdie studie is deel van ‘n kraakspasiëringsverdeling, gedefinieerd deur ‘n spasiëringsgrens. Daarom moet die kraakspasiëringskarakteristieke en spasiëringsgrense in ag geneem word in die ontwerpsproses van ‘n UDAGBP ponsswigting-peilings-model, nie slegs die waarde van die gemiddelde kraakspasiëring nie. Sleutel woorde: UDAGBP, VPT, Gemiddelde Kraakspasiëring, Ponsswigting, Beskrywende Statistiek, cncPave, M-E POG, Transversale Krake, Digte Vloeistof Fondasie, Elasties- Soliede Fondasie.
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Hebdon, Aubrey Lynne. "Evaluation of Concrete Bridge Decks Comprising Twisted Steel Micro Rebar." BYU ScholarsArchive, 2021. https://scholarsarchive.byu.edu/etd/8788.
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The objective of this research was to investigate the effects of twisted steel micro rebar (TSMR) fibers on 1) the mechanical properties of concrete used in bridge deck construction and 2) the early cracking behavior of concrete bridge decks. This research involved the evaluation of four newly constructed bridge decks through a series of laboratory and field tests. At each location, one deck was constructed using a conventional concrete mixture without TSMR, and one was constructed using the same conventional concrete mixture with an addition of 40 lb of TSMR per cubic yard of concrete. Regarding laboratory testing, the conventional and TSMR beam specimens exhibited similar average changes in height after 4 months of shrinkage testing. The electrical impedance measurements did not indicate a notable difference between specimens comprising concrete with TSMR and those comprising conventional concrete. Although no notable difference in behavior between conventional and TSMR specimens was apparent before initial cracking, the toughness of the TSMR specimens was substantially greater than that of the conventional concrete specimens. Regarding field testing, sensors installed in the bridge decks indicated that the addition of TSMR does not affect internal concrete temperature, moisture content, or electrical conductivity. The average Schmidt rebound number varied little between the TSMR decks and conventional decks; therefore, the stiffness of the TSMR concrete was very similar to that of conventional concrete. Distress surveys showed that the conventional decks exhibited notably more cracking than the TSMR decks. The TSMR fibers exhibited the ability to limit both crack density and crack width. For all of the decks, chloride concentrations increased every year as a result of the use of deicing salts on the bridge decks during winter. However, the chloride concentrations for samples collected over cracked concrete increased more rapidly than those for samples collected over non-cracked concrete. Although TSMR fibers themselves do not directly affect the rate at which chloride ions penetrated cracked or non-cracked concrete, the fibers do prevent cracking, which, in turn, limits the penetration of chloride ions into the decks. Therefore, the use of TSMR would be expected to decrease the area of a bridge deck affected by cracking and subsequent chloride-induced corrosion damage and thereby increase the service life of the bridge deck.
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Prakash, Shruthi. "Nonlinear Finite Element Analysis of Shrinking Reinforced Concrete Slabs-on-ground." Thesis, KTH, Betongbyggnad, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-231361.
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Concrete slabs-on-ground are commonly used in many types of industrial floors, warehouses, highways, parking lots and buildings. Cracks and deflection of slabs are undesired events caused by differential shrinkage, which limits the service life of the slabs. Non-linear behavior of cracks and deflections, interaction of concrete and reinforcement increase the complexity in predicting the occurrence and positioning of cracks. The Eurocode 2 provides a reference for theoretical approximation for design of concrete structures. This thesis intent to investigate the crack behavior of slabs-on-ground subjected to gradient shrinkage using nonlinear finite element analysis, as implemented in the software package Atena 2D. The first part of the thesis is focused on suitable modeling techniques for predicting cracks in concrete slabs-on-ground due to gradient shrinkage. The second part is directed towards parametric studies, performed to explore the significance of varying thickness, length, concrete strength class, bond types, reinforcement content and friction coefficient. The results obtained with the Atena 2D was validated using the design software WIN-statik for calculating the maximum crack width in the context of obtaining realistic results. Finally, the WSP guide recommended parameters were tested as inputs to the model. A slab-on-ground was modeled in Atena 2D considering these as statically indeterminate structures, where both slab and grade were included and the convergence analysis performed under plane stress conditions enabling prediction of the maximum crack widths for increasing applied shrinkage loads. Parametric studies demonstrate the dependency of the slab length, showing that a smaller length reduces the crack width, since such a slab is less constrained by the sub-base. To avoid cracks in the slabs their relative thickness should not be increased above a certain thickness, instead the reinforcement content should be increased. The numerical simulation shows that different concrete strength classes give similar cracks widths. Sand as sub-base provides less crack widths for interface materials EPS, sand and gravel. Although, dry sand as interface material gives similar crack widths as EPS, it is the best to use EPS that is also used to retard the moisture diffusion from the sub-base. The numerical model developed was validated for the recommended values given by the WSP guide, which gives less crack widths and deflections. The numerical model gives less crack widths compared to the Eurocode 2, which considers only the statistically determinant problems overestimating the crack widths. The presented examples demonstrate that the developed model can accurately predict crack formation, crack behavior and vertical deflection in concrete slabs-on-ground subjected to gradient shrinkage loads.
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Kluyts, Grant. "Investigation of the effect of selected polypropylene fibres and ultra-fine aggregate on plastic shrinkage cracks on South African roads." Thesis, Nelson Mandela Metropolitan University, 2005. http://hdl.handle.net/10948/174.
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Plastic shrinkage cracks, although not inherently structurally debilitating, expose the reinforcement in low-volume reinforced concrete roads to deleterious substances, which may reduce its effectiveness leading ultimately to structural failure. In un-reinforced low-volume concrete road these cracks appear unsightly and cause the road user an unpleasant riding experience. Many researchers believe that plastic shrinkage crack development remains a concern to the concrete industry, occurring in particularly large–area pours such as low-volume concrete roads, and therefore requires further research to understand their formation and minimization. This study reports findings on the effectiveness of oxyfluorinated polypropylene fibres to control plastic shrinkage cracks, and the effect the addition of ultra-fine material has on the formation and/or propagation of these cracks. Findings indicate that low volume dosages (2 kg/m³), of oxyfluorinated polypropylene fibre significantly reduced the formation of plastic shrinkage cracks under test conditions. Furthermore, that the addition of ultra-fine material in excess of 63 kg/m³ increased the formation and/or development of plastic shrinkage cracks.
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Mondo, Eleonora. "Shear Capacity of Steel Fibre Reinforced Concrete Beams without Conventional Shear Reinforcement." Thesis, KTH, Bro- och stålbyggnad, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-41016.
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While the increase in shear strength of Steel Fibre Reinforced Concrete (SFRC) is well recognized, it has yet to be found common application of this material in building structures and there is no existing national standard that treats SFRC in a systematic manner. The aim of the diploma work is to investigate the shear strength of fibre reinforced concrete beams and the available test data and analyse the latter against the mostpromising equations available in the literature. The equations investigated are:Narayanan and Darwish’s formula, the German, the RILEM and the Italian guidelines. Thirty articles, selected among over one hundred articles taken from literature, have been used to create the database that contains almost 600 beams tested in shear. This large number of beams has been decreased to 371 excluding all those beams and test that do not fall within the limitation stated for this thesis. Narayanan and Darwish’s formula can be utilized every time that the fibre percentage, the type of fibres, the beam dimensions, the flexural reinforcement and the concrete strength class have been defined. On the opposite, the parameters introduced in the German, the RILEM and the Italian guidelines always require a further characterization of the concrete (with bending test) in order to describe the post‐cracking behaviour. The parameters involved in the guidelines are the residual flexural tensile strengths according to the different test set‐ups. A method for predicting the residual flexural tensile strength from the knowledge of the fibre properties, the cylindrical compressive strength of the concrete and the amount of fibres percentage is suggested. The predictions of the shear strength, obtained using the proposed method for the residual flexural tensile strength, showed to be satisfactory when compared with the experimental results. A comparison among the aforementioned equations corroborate the validity of the empirical formulations proposed by Narayanan and Darwish nevertheless only the other equations provide a realistic assessments of the strength, toughness and ductility of structural elements subjected to shear loading. Over the three investigated equations, which work with the post‐cracking characterization of the material, the Italian guideline proposal is the one that, due to its wide domain of validity and the results obtained for the gathered database of beams, has been selected as the most reliable equation.
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Shaarbaf, Ihsan Ali Saib. "Three-dimensional non-linear finite element analysis of reinforced concrete beams in torsion : reinforced concrete members under torsion and bending are analysed up to failure : a non-linear concrete model for general states of stress including compressive strength degradation due to cracking is described." Thesis, University of Bradford, 1990. http://hdl.handle.net/10454/3576.
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This thesis describes a non-linear finite element model suitable for the analysis of reinforced concrete, or steel, structures under general three-dimensional states of loading. The 20 noded isoparametric brick element has been used to model the concrete and reinforcing bars are idealised as axial members embedded within the concrete elements. The compressive behaviour of concrete is simulated by an elasto-plastic work hardening model followed by a perfectly plastic plateau which is terminated at the onset the . crushing. In tension, a smeared crack model with fixed orthogonal cracks has been used with the inclusion of models for the retained post-cracking stress and the reduced shear modulus. The non-linear equations of equilibrium have been solved using an incremental-iterative technique operating under load control. The solution algorithms used are the standard and the modified Newton-Raphson methods. Line searches have been implemented to accelerate convergence. The numerical integration has been generally carried out using 15 point Gaussian type rules. Results of a study to investigate the performance of these rules show that the 15 point rules are accurate and computationally efficient compared with the 27(3X3X3) point Gaussian rule. The three- dimensional finite element model has been used to investigate the problem of elasto-plastic torsion of homogeneous members. The accuracy of the finite element solutions obtained for beams of different cross-sections subjected to pure and warping torsion have been assessed by comparing them with the available exact or approximate analytical solutions. Because the present work is devoted towards the analysis of reinforced concrete members which fail in shear or torsional modes, the computer program incorporates three models to account for the degradation in the compressive strength of concrete due to presence of tensile straining of transverse reinforcement. The numerical solutions obtained for reinforced concrete panels under pure shear and beams in torsion and combined torsion and bending reveal that the inclusion of a model for reducing the compressive strength of cracked concrete can significantly improve the correlation of the predicted post-cracking stiffness and the computed ultimate loads with the experimental results. Parametric studies to investigate the effects of some important material and solution parameters have been carried out. It is concluded that in the presence of a compression strength reduction model, the tension-stiffening parameters required for reinforced concrete members under torsion should be similar to those used for members in which bending dominates.
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Piyasena, Ratnamudigedara, and n/a. "Crack Spacing, Crack Width and Tension Stiffening Effect in Reinforced Concrete Beams and One-Way Slabs." Griffith University. School of Engineering, 2003. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20030606.165418.
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An analytical method for determining the crack spacing and crack width in reinforced concrete beams and one-way slabs is presented in this thesis. The locations and the distribution of cracks developed in a loaded member are predicted using the calculated concrete stress distributions near flexural cracks. To determine the stresses, a concrete block bounded by top and bottom faces and two transverse sections of the beam is isolated and analysed by the finite element method. Two types of blocks are analysed. They are: (i) block adjacent to the first flexural crack, and (ii) block in between successive cracks. The calculated concrete stress distribution adjacent to the first flexural crack is used to predict the locations of primary cracks (cracks formed at sections where the stresses have not been influenced by nearby cracks). The concrete stress distributions in between successive cracks, calculated for various crack spacings and load levels, are used to predict the formation of secondary cracks in between existing cracks. The maximum, minimum and the average crack spacing at a given load level are determined using the particular crack spacing that would produce a concrete tensile stress equal to the flexural strength of concrete. The resulting crack width at reinforcement level is determined as the relative difference in elastic extensions of steel and surrounding concrete. The accuracy of the present method is verified by comparing the predicted spacing and width of cracks with those measured by others. The analytical method presented in this thesis is subsequently used to investigate the effects of various variables on the spacing and width of cracks, and the results are presented. These results are used to select the set of parameters that has the most significant effect. A parametric study is then carried out by re-calculating the spacing and width of cracks for the selected parameters. Based on the results of this parametric study, new formulas are developed for the prediction of spacing and width of cracks. The accuracy of these formulas is ascertained by comparing the predicted values and those measured by other investigators on various types of beams under different load levels. The calculated stress distributions between successive cracks are also used to develop a new method of incorporating the tension stiffening effect in deflection calculation. First, curvature values at sections between adjacent cracks are determined under different load levels, using the concrete and steel stresses. These results are used to develop an empirical formula to determine the curvature at any section between adjacent cracks. To verify the accuracy of the new method, short-term deflections are calculated using the curvature values evaluated by the proposed formula for a number of beams, and the results are compared with those measured by others.
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Kassimi, Fodhil. "Development and performance of fiber-reinforced self-consolidating concrete for repair applications." Thèse, Université de Sherbrooke, 2013. http://hdl.handle.net/11143/6636.
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Abstract: The use of self-consolidating concrete (SCC) in the concrete industry in cast-in-place applications, including repair applications, is growing given the various advantages offered in both fresh and hardened states. The present study deals with the design and performance of fiber-reinforced self-consolidating concrete (FR-SCC) as a repair material of concrete infrastructure. The study also considers the use of various steel and synthetic fibers (five fibers in total) that were used to produce FR-SCC and fiber-reinforced self-consolidating mortar (FR-SCM) that can be employed for structural and non-structural repair applications. The study evaluates the effect of material properties and mixture composition of the fibrous concrete and mortar on workability, mechanical, visco-elastic, durability, and structural behavior. The investigation that is presented in this thesis included the testing of 28 full-scale beams under four-point flexural loading. The majority of these beams were repaired by casting concrete to fill a relatively thin section along the tension zone of the beams. The repair technique was based on the FR-SCC characteristics including the maximum fiber volume and length. This technique required mixtures of high range of fluidity. The optimized FR-SCC and FR-SCM mixtures exhibited excellent flow characteristics along the 3.2-m long beams without blockage, segregation, nor debonding at the interface of repair-substrate concrete. Based on the structural characteristics of the composite beams, the overall performance of the beams repaired using the FR-SCC and FR-SCM was similar or higher (up to 2.6 times) than that of monolithic beams made with conventional vibrated concrete (CVC). The use of optimized FRSCC mixtures enabled the replacement of 50% of the tension steel reinforcement in repair sections; i.e., the number of bars in the tension zone decreased from three bars to two bars with the addition of fibers in the SCC without mitigating structural performance. The degree of prediction of crack width, cracking load/moment, ultimate loads, and deflection of various FR-SCC and FR-SCM mixture was evaluated using several design and code models. The results indicate that these code models can provide safe predictions for crack and ultimate loads, as well as crack width of FR-SCC. The deflection of FR-SCC is unsafe but predictable by these code models. In total, 18 large-scale beams were tested in four-point for flexural creep. FR-SCC incorporating steel fibers combined with expansive agent provided overall performance up to 10 times of that obtained with CVC with the same fiber type and volume. The cracking under constant load was reduced by 60% to 80% using self-consolidating fibrous mixtures made with or without expansion agents, compared to SCC without fibers. The best combination to reduce the cracking potential when the restrained shrinkage ring test was employed was obtained with SCC mixtures made with steel fibers and expansive agent. Models were elaborated to predict the time-to-cracking for FR-SCC and FR-SCM mixtures based on mixture modulus of elasticity and drying and autogenous shrinkages. The project involved extensive testing of highly flowable fibrous materials to determine drying shrinkage (nearly 260 prisms), modulus of rupture (nearly 180 prisms), as well as compressive and splitting tensile strengths and elastic modulus (nearly 2100 cylinders). Based on the results, models were proposed to predict these key material properties that affect the performance of FR-SCC and FR-SCM used in repair applications. In addition to FR-SCC, the investigation also was set to evaluate the feasibility of using fiber-reinforced superworkable concrete (FR-SWC) in construction and repair applications. Such highly flowable concrete that requires limited vibration consolidation can represent some advantages over FR-SCC (lower admixtures demand, lower risk of segregation, greater robustness, lower formwork pressure, etc.). The energy needed to ensure proper consolidation, using either vibration or rodding, applied on samples made with FR-SWC was determined. The energy requirement took into consideration the development of mechanical properties, the resistance to segregation, and the development of proper surface quality. The study also demonstrated the higher overall structural performance of optimized FR-SWC compared to the corresponding FR-SCC mixtures. The findings of the thesis on the design and performance of highly workable fiber-reinforced cementitious materials should facilitate the acceptance of such novel high-performance material in infrastructure construction and repair applications. // Résumé: L'utilisation du béton autoplaçant (BAP) dans l'industrie du béton dans les applications du coulage sur place incluant les applications de la réparation, est en croissance vu les divers avantages offerts à l'état frais et à l'état durci. La présente étude traite de la conception et la performance des bétons autoplaçants fibrés (BAPF) en tant que matériau de réparation des infrastructures en béton. L'étude considère également l'usage de différentes fibres métalliques et synthétiques (cinq fibres au total) qui ont été utilisées pour produire des BAPF et des mortiers autoplaçants fibrés (MAPF) pour des applications de réparations structurales et non structurales. L'étude évalue l'effet des propriétés du matériau et la composition des bétons et mortiers fibrés sur l'ouvrabilité, les propriétés mécaniques, viscoélastiques, de durabilité et le comportement structural. L'étude présentée dans cette thèse a inclus 28 poutres à grande échelle testées sous un chargement flexionnel à quatre points. La majorité de ces poutres a été réparée par le coulage du béton pour remplir une section relativement mince tout au long de la zone tendue des poutres. La technique de réparation a été basée sur les caractéristiques des BAPF incluant le volume maximal et la longueur maximale de fibres. Cette technique a requis des mélanges de haut niveau de fluidité. Les BAPF et MAPF ont exhibé d'excellentes caractéristiques d'écoulement le long de 3,2 m, la longueur de la poutre, sans blocage, ségrégation, ni décollement à l'interface entre le béton de base et le béton de réparation. En se basant sur les caractéristiques structurales des poutres composites, la performance globale des poutres réparées en utilisant les BAPF et les MAPF était similaire ou supérieure (jusqu'à 2,6 fois) que celle des poutres monolithiques fabriquées d'un béton conventionnel vibré (BCV). L'utilisation des mélanges de BAPF optimisés a permis de remplacer 50% du ferraillage tendu dans les sections de réparation; c'est-à-dire que le nombre des barres d'armatures dans la zone tendue a réduit de trois barres à deux barres avec l'addition de fibres dans le BAP sans mitiger la performance structurale. Le degré de prédiction de la largeur de fissures, charge de fissuration, charge ultime et déflexion de différents mélanges de BAPF et MAPF a été évalué en utilisant quelques designs et modèles de codes. Les résultats ont montré que ces modèles ont pu fournir de prédictions sécuritaires pour les charges de fissuration et ultime, ainsi que la fissuration des BAPF. La déflexion des BAPF est non sécuritaire mais reste prédictible par ces modèles de codes. En total, 18 poutres à grande échelle ont été testées en fluage flexionnel de quatre points. Des BAPF contenant des fibres métalliques combinées avec un agent expansif ont fourni une performance globale jusqu'à 10 fois celle obtenue avec un BCV contenant le même type et volume de fibres. La fissuration sous une charge constante a été réduite de 60% à 80% en utilisant des mélanges autoplaçants fibrés fabriqués avec ou sans agents expansifs, par rapport au BAP sans fibres. La meilleure combinaison pour réduire le potentiel de fissuration avec l'essai du retrait restreint a été obtenue avec des mélanges de BAP contenant de fibres d'acier et un agent expansif. Des modèles ont été élaborés pour prédire le temps de fissuration des mélanges de BAPF et MAPF basés sur le module d'élasticité du mélange et les retraits de séchage et endogène. Le projet comportait de nombreux essais sur les mélanges fibrés de haute fluidité à savoir la détermination du retrait de séchage (près de 260 prismes), le module de rupture (près de 180 prismes), ainsi que la résistance en compression, la résistance en traction et le module d'élasticité (plus de 2100 cylindres). En se basant sur les résultats, des modèles ont été proposés pour prédire ces propriétés clés qui affectent la performance des BAPF et MAPF destinés aux applications de réparation. En plus des BAPF, l'étude a aussi été faite pour évaluer la faisabilité de l'utilisation des bétons semi-fluides fibrés (BSFF) dans les applications de construction et de réparation. Tels bétons de haute fluidité requérant une consolidation limitée peuvent présenter certains avantages par rapport aux BAPF (plus faible demande en adjuvants, plus faible risque de ségrégation, robustesse supérieure, plus faible pression sur les coffrages, etc.). L'énergie nécessaire pour assurer une propre consolidation, en utilisant soit la vibration ou le piquage, appliquée sur des échantillons de BSFF a été déterminée. Les exigences de cette énergie considèrent le développement des propriétés mécaniques, la résistance à la ségrégation et la propre qualité de surface. L'étude a aussi démontré une performance structurale globale supérieure des BSFF optimisés par rapport aux mélanges de BAPF correspondant. Les conclusions de la thèse sur le design et la performance des matériaux cimentaires renforcés de fibres et de haute fluidité devraient faciliter l'acceptation de tels nouveaux matériaux de haute performance dans les applications de la construction et la réparation des infrastructures.
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Brisotto, Daiane de Sena. "Um modelo de fissura incorporada para análise da fissuração em peças de concreto armado fletidas via método dos elementos finitos." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2006. http://hdl.handle.net/10183/11166.
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A análise da formação e crescimento de fissuras em peças de concreto armado permanece como uma das principais dificuldades no campo da engenharia estrutural. Considerando que as fissuras têm uma influência muito grande no comportamento estrutural global, estudos para prever e controlar a fissuração do concreto são de essencial importância. O objetivo deste trabalho é apresentar um modelo numérico do tipo incorporado para representar as fissuras em peças de concreto armado submetidas aos esforços de flexão e corte, ou seja, um modelo que seja capaz de simular, além das fissuras perpendiculares ao eixo da peça, fissuras inclinadas. Os modelos de fissura incorporada se baseiam no conceito de descontinuidades incorporadas dentro de elementos finitos padrões. No modelo empregado neste trabalho, a fissura é representada através de uma descontinuidade no campo interno de deslocamentos do elemento. O modelo incorporado implementado é uma continuação do trabalho desenvolvido por d’Avila, que baseou-se no modelo de Dvorkin Cuitiño e Gioia que, por sua vez, não inclui a contribuição da armadura no equilíbrio interno de forças do elemento. A interação entre as barras de aço e o concreto é simulada através um modelo de transferência de tensão por aderência entre os dois materiais, conforme Russo, Zingone e Romano e FIB - Bulletin 10. Para representar o comportamento do concreto intacto, utiliza-se o modelo constitutivo de Ottosen. Já para representar as barras de aço da armadura, emprega-se o modelo incorporado desenvolvido por Elwi e Hrudey, que permite uma disposição arbitrária das barras de aço no interior dos elementos de concreto. O modelo constitutivo adotado para a armadura é do tipo elasto-plástico com endurecimento. Foi possível simular a fissuração em flexão e corte em vigas de concreto armado com boa correlação com resultados experimentais. Tais situações não poderiam ser analisadas pelo modelo básico sem as modificações propostas nesta dissertação.The analysis of the formation and growth of cracks in reinforced concrete members remains as one of the main difficulties in the field of structural engineering. Considering that the crack has a considerable influence in the global structural behavior, studies to predict and to control concrete cracking are of essential importance. The aim of this work is to present a numerical model of the embedded type to represent the cracks in reinforced concrete members under bending and shearing efforts, i. e. , a model that is capable to simulate not only cracks that are perpendicular to the axle of the members but also inclined cracks. The embedded crack models are based on the concept of incorporated discontinuities inside of standard finite elements. In the model used in this work, the crack is represented by a discontinuity in the internal field of the element displacements. The embedded model proposed is a continuation of the work developed by d’Avila, which is based on the model of Dvorkin, Cuitiño e Gioia, that does not consider the inclusion of the reinforced contribution in the internal force equilibrium of the element. A bond stress-transfer approach is used to include this reinforcement contribution. To represent the behavior of the uncracked concrete, the Ottosen constitutive model was used. The embedded model presented by Elwi and Hrudey was employed to represent the reinforcement bars, that allows an arbitrary disposal of the bars of steel inside of the concrete elements. The constitutive model adopted for reinforcement is elasto-plastic with hardening. It was possible to simulate the cracking in bending and shearing in reinforced concrete beams with good agreement with experimental results. These cases could not be analyzed by the basi model without the present proposed modifications.
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Brattström, Niels, and Oliver Hagman. "Reinforced Concrete Subjected To Restraint Forces : A comparison with non-linear numerical analyses." Thesis, KTH, Bro- och stålbyggnad, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-209122.
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In Sweden, it is Eurocode 2 which forms the basis for performing a design of concrete structures, in which methods can be found treating the subject of restrained concrete members and cracking in the serviceability limit state. In the code, both detailed hand calculations procedures as well as simplified methods are described. Several proposal of how to treat base restrained structures can be found in other codes and reports. Some state that the procedure given in Eurocode 2 is on the unsafe side as the method relies on stabilized cracking, while some say that the method is over conservative as the restraining actions will prevent the cracks from opening. As these methods are analysed closer and further tested, it is obtained that they all yield different results under the same assumptions. Most of them are within a similar span, and the deviation arises as the various methods takes different aspect into consideration. One method yields a result which is considerably higher than all other, denoted the Chalmers method. As this method is taught at the technical institute of Gothenburg (Chalmers), the large deviation have caused some confusion among Swedish engineers. As the methods are compared to numerical analyses, it is found that the detailed calculation procedure stated in Eurocode 2 yields fairly good prediction of crack widths for lower levels of strain, while for high levels of strain it is over conservative. The Chalmers method seems to underestimate the number of cracks which occur, and thus give rise to the deviating results. It is further found that in relation to more detailed hand calculations, the simplified procedure stated in Eurocode 2 may not always be on the safe side. The procedure is only valid within a certain range which may be exceeded depending on the magnitude of the load and choice of various design parameters. The effect creep have on base restrained structures subjected to long term loads such as shrinkage is further discussed and analysed numerically. Various hand calculation methods suggest that creep have a positive influence on base restrained structures in the sense that the crack width become smaller. The numerical results indicates that this is indeed the case, however, uncertainties of these analyses are considered to be large in relation to the short term analyses.I Sverige är det Eurokod 2 som används som basis för dimensionering av betongkonstruktioner, i vilken metoder som beskriver sprickkontroll i bruksgränsstadiet för betong utsatt för tvångskrafter återfinns. Både detaljerade handberäkningsmetoder och förenklade metoder beskrivs. I olika koder och rapporter återfinns ett flertal förslag till hur detta problem ska hanteras. Vissa påstår att metoderna som anges i Eurokod 2 är på osäkra sidan då dessa förlitar sig på stabiliserad sprickbildning, medan andra menar att Eurokod 2 är för konservativ då inspänningen kommer förhindra att sprickorna öppnar sig. Då metoderna analyseras noggrannare och testas framgår det att alla genererar olika resultat under samma antaganden. De flesta ligger inom samma spann och skillnaderna uppkommer då de olika metoderna beaktar olika aspekter. En metod genererar dock ett resultat som är högre än alla andra, som i denna rapport benämns som Chalmersmetoden. Då denna metod lärs ut på Göteborgs tekniska universitet (Chalmers) så har de utstickande resultatet skapat en viss förvirring bland konstruktörer i Sverige. Då metoderna jämförs med numeriska analyser framgår det att Eurokod 2 förutspår en rimlig sprickvidd för låga töjningsgrader, medan den verkar vara överkonservativ för höga töjningsgrader. Chalmersmetoden verkar underestimera antalet sprickor som uppkommer i konstruktionen, vilket resulterar i de utstickande resultaten. Fortsättningsvis fastslås det att i relation till en mer detaljerad handberäkning så är den förenklade metoden i Eurokod 2 inte alltid på säkra sidan. Metoden är endast giltig inom ett visst spann, vilket kan överskridas beroende på den egentliga töjningens storlek och valet av dimensioneringsparametrar. Krypningens effekt på fastinspända betongkonstruktioner då de utsätts för långtidslaster så som krympning har också diskuterats och analyserats numeriskt. Olika handberäkningsmetoder antyder att krypningen har en positiv effekt på så sätt att sprickvidden minskar. Även de numeriska resultaten indikeratar att så är fallet, dock anses osäkerheten i dessa analyser vara stor i förhållande till analyser av korttidslaster.
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Nguyen, Nhan Hoa. "Dégradation du béton armé sous actions sévères : Etude du comportement résiduel de l’adhérence à l’aide de la technique d’émission acoustique." Thesis, Rennes, INSA, 2014. http://www.theses.fr/2014ISAR0019.
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De nos jours, le béton est le matériau de construction le plus utilisé dans le monde en raison de ses performances mécaniques, sa facilité de mise en oeuvre, son coût compétitif et sa « recyclabilité ». Toutefois, compte tenu de son caractère fragile en terme mécanique et de sa faible résistance à la traction, il est souvent renforcé par des armatures métalliques qui lui confèrent une bonne ténacité et une meilleure aptitude à supporter les efforts de traction. Ce composite béton-armature ne peut cependant assurer efficacement son rôle que si les deux composants sont étroitement liés l’un à l’autre. C’est donc dans la qualité de l’adhérence que réside l’efficacité du transfert des efforts entre les deux matériaux. Or, dès la mise en place des ouvrages en béton armé et pendant toute la durée de leur exploitation, différentes actions et agents agresseurs peuvent modifier la qualité de cette adhérence. Il peut s’agir de phénomènes naturels comme le gel/dégel et l’action du dioxyde de carbone atmosphérique, ou des sollicitations accidentelles comme l’incendie ou encore l’action de certains agents spécifiques comme les chlorures et les sulfates. Notre objectif dans cette thèse est de qualifier les modifications d’adhérence qui résultent de quatre types de sollicitations couramment rencontrées dans la vie des ouvrages en béton armé: l’effet des températures élevées, l’effet de la carbonatation, l’effet des cycles gel/dégel, l’effet de la corrosion. Nous évaluons la qualité de l’adhérence par la mesure de la résistance à l’arrachement et par l’analyse du comportement résiduel sous sollicitation mécanique. La technique d’émission acoustique est utilisée pour localiser en temps réel, l’endommagement du matériau sous sollicitation. Les applications de notre étude concernent non seulement les armatures et inserts classiques du béton armé mais aussi les nombreux dispositifs constructifs des structures mixtes acier – béton qui utilisent les liaisons par goujons pour relier les deux matériauxNowadays, concrete is the most used construction material in the world because of its mechanical performances, its ability to be molded or cast, its competitive cost and its recyclability. However, concrete has a low ductility and a relatively low tensile strength compared to other construction materials. Therefore, concrete is often reinforced by steel rebars to improve the ductility and tensile strength. Nevertheless, to make reinforced concrete being highly efficient material, the two components need to be correctly bonded each to other. The bond quality the efficiency of the force transfer between rebar and concrete surrounding ensures. In fact, since the casting of concrete and during the service life of reinforced concrete structure, various actions such corrosion action, freeze/thaw attack and chemical attack etc. may affect the bond quality. The objective of this PhD research work is to qualify the changes of adhesion property causing by four types of action which frequently takes place in the service life of reinforced concrete structures: the effect of high temperatures, the effect of carbonation, the effect of cycles freeze/thaw, the effect of corrosion. The concrete-rebar bond quality is evaluated by doing pull-out tests under static mechanical action and measuring the bond strength and analyzing residual behaviour. Moreover, the acoustic emission technique is used to locate the cracks and evaluate the cracking evolution in real time. The founding of this study can be also extended to apply to other concrete-steel structures like composite structures in which headed studs are used to connect steel profiles to concrete
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Gribniak, Viktor. "Susitraukimo įtaka gelžbetoninių elementų tempiamosios zonos elgsenai." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2009. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2009~D_20091102_090253-50712.
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Pastaraisiais metais vis plačiau taikant stiprųjį betoną bei armatūrą, konst-rukcijų perdengiamos angos didėja, o skerspjūviai mažėja. Todėl projektuojant standumo (įlinkių) sąlyga vis dažniau tampa lemiamu veiksniu. Inžinieriai gelž-betoninių konstrukcijų apskaičiavimams gali taikyti empirinius normų arba skai-tinius metodus. Vieno ar kito skaičiavimo metodo parinkimas turi būti pagrįstas statistiniais tikslumo analizės rezultatais.
Yra žinoma, kad adekvatus gelžbetoninio elemento pleišėjimo (ypač plyšių vystymosi stadijos) modeliavimas yra vienas sudėtingiausių netiesinės mechani-kos uždavinių. Toks uždavinys gali būti išspręstas taikant vidutinių plyšių kon-cepciją, kai pleišėjimo proceso modeliavimui naudojama tempiamojo betono vidutinių įtempių ir deformacijų diagrama. Dauguma tokių diagramų gautos, naudojant tempimo arba šlyties bandymo rezultatus. Pabrėžtina, kad šių diagra-mų taikymas lenkiamųjų gelžbetoninių elementų modeliavime duoda nemažas paklaidas. Kitas svarbus aspektas yra tai, kad gelžbetoniniuose bandiniuose, iki juos apkraunant trumpalaike apkrova, vyksta betono susitraukimas. Šiame darbe buvo siekiama sukurti metodą, leidžiantį pagal eksperimentinius lenkiamųjų gelžbetoninių elementų duomenis gauti tempiamojo betono vidutinių įtempių ir deformacijų diagramas, įvertinant betono susitraukimo įtaką. Pagrindinis diser-tacijos tikslas yra įvertinti ikieksploatacinių betono susitraukimo ir valkšnumo poveikį gelžbetoninių elementų, apkrautų trumpalaike apkrova... [toliau žr. visą tekstą]Due to the use of refined ultimate state theories as well as high strength concrete and reinforcement, resulting in longer spans and smaller depths, the serviceability criteria often limits application of modern reinforced concrete (RC) superstructures. In structural analysis, civil engineers can choose between traditional design code methods and numerical techniques. In order to choose a particular calculation method, engineers should be aware of accuracy of differ-ent techniques. Adequate modelling of RC cracking and, particularly, post-cracking behaviour, as one of the major sources of nonlinearity, is the most im-portant and difficult task of deformational analysis. In smeared crack approach dealing with average cracking and strains, post-cracking effects can be modelled by a stress-strain tension-stiffening relationship. Most known tension-stiffening relationships have been derived from test data of shrunk tension or shear mem-bers. Subsequently, these constitutive laws were applied for modelling of bend-ing elements which behaviour differs from test members. Furthermore, such re-lationships were coupled with shrinkage effect. Therefore, present research aims at developing a technique for deriving a free-of-shrinkage tension-stiffening re-lationship using test data of shrunk bending RC members. The main objective of this PhD dissertation is to investigate shrinkage influence on deformations and tension-stiffening of RC members subjected to short-term loading. Present... [to full text]
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Carlesso, Débora Martinello. "Flexural fatigue of pre-cracked fibre reinforced concrete: experimental study and numerical modelling." Doctoral thesis, Universitat Politècnica de Catalunya, 2020. http://hdl.handle.net/10803/669488.
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Fibre reinforced concrete (FRC) is recognized as suitable material for structural applications. The number of national codes that have approved it is an evidence. Structures where FRC is generally used can be subjected to fatigue loads and are expected to resist millions of cycles during their service life. Cyclic loads affect significantly the characteristics of materials and can cause fatigue failures. The most demanded cross-sections being cracked under tensile stresses due to direct loads or imposed deformations. Commonly, publications report fatigue behaviour of concrete under compression and are valid for uncracked sections. Imprecision in fatigue prescriptions are reflected through formulation of models that contemplate a probabilistic approach, or an introduction of high safety coefficients within construction codes. The aim of the present doctoral thesis is to perform a structural design oriented analysis on the behaviour of pre-cracked FRC subjected to flexural fatigue loads. FRC with steel and polypropylene fibre with different volume content were investigated by means of three-point bending tests, considering an initial crack width accepted in the service limit state. The mechanical behaviour of FRC were analysed in terms of applied load level, crack opening displacement (CMOD) and fatigue life. The residual flexural tensile strength was assessed after these tests to estimate the impact of the cycles in the remaining resistant capacity of the specimens. Results suggest that the mechanism of crack propagation is independent of the fibre type and content and the monotonic load-crack opening displacement curve might be used as deformation failure criterion for FRC under flexural fatigue loading. The conducted probabilistic approach allows predicting the fatigue strength of concrete reinforced with steel fibres. The findings postulate the proposal of a model to predict the evolution of the crack-opening and the remaining resistant capacity. An optimisation procedure is proposed to derive the model parameters using a limited number of initial load cycles. This doctoral thesis provides knowledge and data that may aid further research and contribute to the future development of design recommendations.El hormigón reforzado con fibra (FRC) se reconoce como material adecuado para aplicaciones estructurales. El número de normativas que lo han aprobado es una evidencia. Las estructuras donde generalmente se usa FRC pueden estar sujetas a cargas de fatiga y se espera que resistan millones de ciclos durante su vida útil. Las cargas cíclicas afectan significativamente a las características de los materiales y pueden causar roturas por fatiga. Las secciones transversales más demandadas se fisuran bajo tensión debido a cargas directas o deformaciones impuestas. Comúnmente, las publicaciones informan del comportamiento de fatiga del hormigón bajo compresión y son válidas para secciones no fisuradas. La imprecisión de las recomendaciones se refleja a través de la formulación de modelos que contemplan un enfoque probabilístico o la introducción de altos coeficientes de seguridad dentro de los códigos de construcción. El objetivo de la presente tesis doctoral es realizar un análisis orientado al diseño estructural sobre el comportamiento del FRC pre-fisurado sometido a cargas de fatiga por flexión. Se investigaron FRC con fibras de acero y polipropileno con diferentes contenidos de fibras mediante pruebas de flexotracción a tres puntos, considerando un ancho de fisura inicial aceptado en el estado límite de servicio. El comportamiento mecánico del FRC se analizó en términos de nivel de carga aplicada, desplazamiento de apertura de fisura (CMOD) y vida útil bajo fatiga. La resistencia residual a flexotracción se evaluó después de los ciclos de fatiga para estimar el impacto de los ciclos en la capacidad de resistencia restante de las muestras. Los resultados sugieren que el mecanismo de propagación de fisuras es independiente del tipo y contenido de fibra y la curva monotónica de CMOD podría ser utilizada como criterio de falla de deformación para FRC bajo carga de fatiga por flexotracción. El enfoque probabilístico realizado permite predecir la resistencia a la fatiga del hormigón reforzado con fibras de acero. Los resultados postulan la propuesta de un modelo para predecir la evolución de la apertura de fisura y la capacidad resistente remanente. Se propone un procedimiento de optimización para derivar los parámetros del modelo utilizando un número limitado de ciclos de carga inicial. Esta tesis doctoral proporciona conocimiento y datos que pueden ayudar a futuras investigaciones y contribuir al desarrollo futuro de recomendaciones de diseño.
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Adendorff, Christo Johan. "The time-dependent cracking behaviour of strain hardening cement-based composite." Thesis, Stellenbosch: University of Stellenbosch, 2009. http://hdl.handle.net/10019.1/2847.
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Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2009.ENGLISH ABSTRACT: Strain Hardening Cement-based Composite (SHCC) is part of the High Performance Fibre Reinforced Cement-based Composite (HPFRCC) family and is a relative new concrete composite. This Fibre Reinforced Cement-based Composite (FRCC) contains randomly distributed short fibres and when subjected to a uni-axial tensile load multiple cracking occurs. The multiple cracking generates fine cracks which are normally smaller than 100 μm and achieve a strain capacity of more than 5 %. There are limited publications regarding the research of sustained tensile tests on SHCC and especially the cracking behaviour of SHCC under quasi-static uni-axial as well as sustained tensile loads. The cracking behaviour is described as the average crack width, number of cracks and descriptive statistical properties which could be used to represent the distribution of the multiple fine cracks under uni-axial tension. There are two types of tests that were under consideration to determine the cracking behaviour of SHCC. The first is quasi-static uniaxial tensile tests and the second is sustained tensile tests. The latter was dependant on the uni-axial tensile tests in terms of the sustained load applied. The sustained loads ranged from 40 % to 80 % of the ultimate tensile resistance recorded from the uni-axial tensile tests that correspond with a strain rate of 0.001 /s. Different strain rates were used for the uni-axial tensile tests to determine the effect on the cracking behaviour. The cracking behaviour was determined with the aid of a non-contact optical 3D digital deformation measuring device called ARAMIS. The content of this thesis gives a background study of the cracking behaviour and relevant research performed on SHCC under certain loads as well as some literature about the timedependant effects of a cement-based composite. The functioning of the device called ARAMIS is explained as well as the resulting effects of this device on the preparation of the test specimens. The experimental framework for the uni-axial and sustained tensile tests is discussed. Thereafter, the experimental results of the tests are depicted and discussed. The results shed some light on the basic material properties such as the average ultimate stress and average ultimate strain, Young’s modulus, etc. for the quasi-static tensile tests as well as shrinkage and creep of SHCC. The cracking behaviour such as the average crack width, number of cracks, the variance and skewness of the distribution of the crack widths in the test specimens for the quasi-static uni-axial and sustained tensile tests are depicted and discussed. The cracking behaviour when subjected to uni-axial tensile tests with different strain rates is significantly governed by the formation of new cracks and the average crack width remains small with increase in strain. There is no significant difference for the cracking behaviour found when subjected to different strain rates. However, when SHCC is subjected to a sustained load then the average crack width is dependant on the number of cracks that form over time as well as the load level. The formation of fewer and wider cracks was observed for specimens loaded at average 40 % of the ultimate tensile resistance stress, however at loading percentages of higher than 65 % more cracks developed which resulted in a smaller average crack width.
AFRIKAANSE OPSOMMING: Vervorming Verharding Sement gebaseerde samestelling “Strain Hardening Cement-based Composite” (SHCC) is deel van die familie van “High Performance Fibre Reinforced Cement-based Composite” (HPFRCC) en is ʼn relatiewe nuwe beton samestelling. Hierdie vesel versterkte sement gebaseerde beton bevat willekeurig verspreide kort vesels en veelvoudige klein krake vorm onder monotoniese trekkragte. Hierdie veelvoudige klein krake is minder as 100 μm wyd en lei tot ʼn vervorming van meer as 5 %. Daar is ʼn tekort aan navorsing oor die kruip van SHCC sowel as die kraak gedrag van hierdie sement gebaseerde samestelling onderhewig aan trek. Die kraak gedrag word beskryf as die gemiddelde kraakwydte, aantal krake en ʼn paar beskrywende statistiese parameters. Hierdie kraak gedrag parameters kan gebruik word om ʼn verdeling te kan weergee van die veelvoudige klein krake onder ʼn trek belasting. Twee tipes toetse was uitgevoer om die kraak gedrag te beskryf. Die eerste tipe toets was monotoniese trek toetse en die tweede tipe was kruip toetse. Die tweede toets was afhanklik van die monotoniese trek toetse in terme van die belasting wat gebruik was vir die kruip toetse. Die belasting was gevarieer vanaf 40 % tot 80 % van die breekbelasting wat bepaal is met die monotoniese trektoetse wat ooreenstem met ʼn vervorming tempo van 0.001 /s. Verskillende vervorming tempo’s vir die monotoniese trektoetse was uitgevoer om te bepaal wat die effek is op die kraak gedrag. Die kraak gedrag was bepaal met behulp van ʼn geen-kontak optiese 3D digitale deformasie meet instrument genoem ARAMIS. Die inhoud van die tesis bevat ʼn kort opsoming oor ʼn agtergrond studie van die kraak gedrag en relevante navorsing oor vesel versterkte sement gebaseerde beton, sowel as literatuur oor die tydafhanklike effekte van ʼn sement gebaseerde samestelling. Die beheer en gebruik van die meet instrument ARAMIS word verduidelik, sowel as die effek van hierdie masjien op die voorbereiding vir die eksperimente. Die eksperimentele uiteensetting vir die monotoniese en kruip toetse word beskryf. Daarvolgens is die resultate van die eksperimentele toetse getoon en verduidelik. Die resultate verduidelik die basiese materiaal eienskappe, byvoorbeeld die gemiddelde breekspanning met die ooreenkomstige breekvervorming, Young’s modulus en so voorts vir die monotoniese trektoetse, sowel as eienskappe met betrekking tot krimp en kruip van SHCC. Die kraak gedrag naamlik die gemiddelde kraakwydte, aantal krake per meter, variansie en die skuinsheid van die ontwikkelde krake met die toets proefstukke vir die monotoniese en kruip trek toetse word weergegee en verduidelik. Die kraak gedrag van SHCC wanneer getoets word met verskillende monotoniese trektoets tempo’s word beheer deur die ontwikkeling van nuwe krake en die gemiddelde kraakwydte is beduidend laag met toenemende vervorming. Daar is geen beduidende verskil in die kraak gedrag ten opsigte van die verskillende monotoniese trek tempo’s nie. In teendeel, wanneer SHCC belas word met ʼn konstante las oor tyd word die gemiddelde kraakwydte beheer deur die ontwikkeling van nuwe krake sowel as die belasting wat aangewend is. Onder ʼn belasting van so laag as 40 % van die breekbelasting vorm daar minder krake, maar met ʼn groter gemiddelde kraakwydte. Wanneer belas word met meer as 65 % van die breekbelasting vorm meer krake wat lei tot ʼn kleiner gemiddelde kraakwydte.
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Azzam, Aussama, and Mike Richter. "Investigation of Stress Transfer Behavior in Textile Reinforced Concrete with Application to Reinforcement Overlapping and Development Lengths." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-77838.
Full textAbstract:
Die kontinuumsmechanische Untersuchung der Lastübertragungsmechanismen zwischen den Rovings im textilbewehrten Feinbeton trägt wesentlich zum Gesamtverständnis des mechanischen Verhaltens des Verbundmaterials bei. Neben der Erfassung der gegenseitigen Beeinflussung sich kreuzender Rovings erfordert insbesondere die mechanische Modellierung und numerische Simulation von Bewehrungsstößen und Endverankerungen die Kenntnis dieser Übertragungsmechanismen. Die numerischen Simulationen sollen u. a. zeigen, welche Endverankerungslängen und welche Übergreifungslängen an Bewehrungsstößen erforderlich sind und wie die Querbewehrung die Rissbildung beeinflusstThis paper concerns with the investigation of stress transfer mechanisms between yarns and concrete matrix and their influence on the overall behavior of textile reinforced concrete (TRC). This investigation considers textile reinforcement splices and textile reinforcement development lengths and carried out by means of Finite-Element simulations and fracture mechanic approaches. A first modeling procedure is made towards analyzing and investigating the damage mechanisms in TRC specimen under tension loading which are mainly characterized by matrix cracking and yarn pullout. This modeling approach allows for considering the yarn crack bridging which is a main characteristic behavior of TRC. In the same manner, 3D Finite-Element models are conducted for calculating the required reinforcement development lengths and the reinforcement overlapping lengths. The conducted approach takes into account different damage mechanisms observed in the corresponding experimental investigations which are also used for calibrating the modeling procedures. Moreover, the presented approach covers a wide range of required textile reinforcement overlapping lengths and development lengths and provides the corresponding ultimate loads