Tesis sobre el tema "Shear Behaviour of SCFRC Beams"

When subjected to a combination of moment and shear force, a reinforced concrete (RC) beam with either little or no transverse reinforcement can fail in shear before reaching its full flexural strength. This type of failure is sudden in nature and usually disastrous because it does not give sufficient warning prior to collapse. To prevent this type of shear failure, reinforced concrete beams are traditionally reinforced with stirrups. However, the use of stirrups is not always cost effective since it increases labor costs, and can make casting concrete difficult in situations where closely-spaced stirrups are required. The use of steel fiber reinforced concrete (SFRC) could be considered as a potential alternative to the use of traditional shear reinforcement. Concrete is very weak and brittle in tension, SFRC transforms this behaviour and improves the diagonal tension capacity of concrete and thus can result in significant enhancements in shear capacity. However, one of the drawbacks associated with SFRC is that the addition of fibers to a regular concrete mix can cause problems in workability. The use of self-consolidating concrete (SCC) is an innovative solution to this problem and can result in improved workability when fibers are added to the mix. The thesis presents the experimental results from tests on twelve slender self-consolidating fiber reinforced concrete (SCFRC) beams tested under four-point loading. The results demonstrate the combined use of SCC and steel fibers can improve the shear resistance of reinforced concrete beams, enhance crack control and can promote flexural ductility. Despite extensive research, there is a lack of accurate and reliable design guidelines for the use of SFRC in beams. This study presents a rational model which can accurately predict the shear resistance of steel fiber reinforced concrete beams. The thesis also proposes a safe and reliable equation which can be used for the shear design of SFRC beams.

This thesis presents the results of an experimental, numerical and analytical study to develop a design method to calculate shear resistance of flanged ferrocement beams with vertical mesh reinforcements in the web. Two groups of full-scale testing were conducted comprising of three I beams and four U beams. The I beams had the same geometry and reinforcement arrangements, but differed in the matrix strength or shear span to depth ratio. The U beams differed in web and flange thickness, reinforcement arrangements, matrix strength and shear span to depth ratio. The experimental data were used for validation of finite element models which had been developed using the ABAQUS software. The validated models were subsequently employed to conduct a comprehensive parametric study to investigate the effects of a number of design parameters, including the effect of matrix strength, shear span to depth ratio, cross sectional area, length of clear span, volume fraction of meshes and amount of rebar. The main conclusion from the experiments and parametric studies were: shear failure may occur only when the shear span to depth ratio is smaller than 1.5; the shear strength may increase by increasing the matrix strength, volume fraction of meshes, cross sectional area and amount of rebar. The main type of shear failure for I beams was diagonal splitting while for U beams it was shear flexural. Based on the results from the experimental and numerical studies, a shear design guide for ferrocement beams was developed. A set of empirical equations for the two different failure types and an improved strut-and-tie were proposed. By comparison with the procedures currently in practice, it is demonstrated that the methodology proposed in this thesis is likely to give much better predictions for shear capacity of flanged ferrocement beams.

RC deep beams are key safety critical structural systems carrying heavy loads over short span, such as transfer girders in tall buildings and bridges. Current design provisions in codes of practice fail to predict accurately and reliably the shear capacity of RC deep beams and in some cases they are unsafe. This work aims to develop a better understanding of the behaviour of RC deep beams and governing parameters, and to improve existing design methods to more accurately predict the shear capacity of such members. An extensive experimental programme examining 24 RC deep beams is carried out. The investigated parameters include concrete strength, shear span to depth ratio, shear reinforcement and member depth. To develop a better insight on the distribution and magnitude of developed stresses in the shear span, finite element analysis is also performed. The microplane model M4 is implemented as a VUMAT code in ABAQUS to represent the behaviour of concrete in a more reliable manner and validated against experimental tests on RC deep beams. This model is utilised in a parametric study to further investigate the effect of concrete strength, shear span to depth ratio and shear reinforcement. The experimental and numerical results show that concrete strength and shear span to depth ratio are the two most important parameters in controlling the behaviour of RC deep beams, and that shear strength is size dependent. The analysis also shows that minimum amount of shear reinforcement can increase the shear capacity of RC deep beams by around 20% but more shear reinforcement does not provide significant additional capacity. A lateral tensile strain based effectiveness factor is proposed to estimate the strength of the inclined strut to be used in strut-and-tie model. Additionally, node factors to estimate the developed strength in different type of nodes are proposed. The proposed model is evaluated against a large experimental database and the results show that it yields more accurate and reliable results than any of the existing models. The model is characterized by the lowest standard deviations of 0.26 for both RC deep beams with and without shear reinforcement and accounts more accurately for all influencing parameters.

A recent innovation for the shear strengthening of reinforced concrete (RC) beams is to externally bond Carbon Fibre Reinforced Polymer (CFRP) composite plates or strips. This technique has become popular because of the many advantages of CFRP composites such as: high strength-to-weight ratio, good corrosion resistance, and versatility in coping with different sectional shapes and corners. This study focuses on shear strengthening of structural members using CFRP. The understanding of concrete structures designed for strengthening in shear is still an area where uniform design rules do not exist or are treated very briefly. The research programme to study the shear contribution of externally bonded CFRP sheets/strips of RC beams includes laboratory tests of more than twenty-nine beam samples (of an original conceptual model incorporating a shear plane) with beams of different materials: nine aluminium beams, twenty concrete beams, and some timber beams for initial studies. There are twenty-six pure tensile laboratory tests to study bond behaviour between the parent material and CFRP. In addition, there are six pure shear specimens and tests to determine other material properties. The numerical analyses employ the finite element method and many numerical models are developed for simulation of the contribution of the CFRP for shear strengthening and bond strength. On completion of the experimental programme and FE analyses, the resulting information is used to formulate a new proposal for shear strengthening of concrete beams using CFRP. The bond strengths predicted using existing methods and new proposals from this study are compared with experimental data of this study and previous studies, demonstrating that the new proposals are valid and offer improvement over existing methods.

The present research is conducted to investigate the structural behaviour of continuously supported deep beams made with SCC. A series of tests on eight reinforced two-span continuous deep beams made with SCC was performed. The main parameters investigated were the shear span-to-depth ratio, the amount and configuration of web reinforcement and the main longitudinal reinforcement ratio. All beams failed due to a major diagonal crack formed between the applied mid-span load and the intermediate support separating the beam into two blocks: the first one rotated around the end support leaving the rest of the beam fixed on the other two supports. The amount and configuration of web reinforcement had a major effect in controlling the shear capacity of SCC continuous deep beams. The shear provisions of the ACI 318M-11 reasonably predicted the load capacity of SCC continuous deep beams. The strut-and-tie model recommended by different design codes showed conservative results for all SCC continuous deep beams. The ACI Building Code (ACI 318M-11) predictions were more accurate than those of the EC2 and Canadian Code (CSA23.3-04). The proposed effectiveness factor equations for the strut-and-tie model showed accurate predictions compared to the experimental results. The different equations of the effectiveness factor used in upper-bound analysis can reasonably be applied to the prediction of the load capacity of continuously supported SCC deep beams although they were proposed for normal concrete (NC). The proposed three dimensional FE model accurately predicted the failure modes, the load capacity and the load-deflection response of the beams tested.

Continuous beams represent main structural elements in most reinforced concrete (RC) structures such as parking garages and overpass bridges. Deterioration of such structures due to corrosion of steel reinforcement is common in North America. To overcome the corrosion problems, the use of fiber-reinforced polymer (FRP) bars and stirrups becomes a viable alternative to steel reinforcement. However, to date, the shear behaviour of FRP-RC continuous beams has not been explored yet. As such, the objective of this study is to investigate the shear behaviour of such beams. In this study, twenty four full-scale continuous concrete beams were constructed and tested. The test beams had rectangular cross section with 200-mm width and a height of 300, 550 or 850 mm and were continuous over two equal spans. The main investigated parameters were concrete strength, type and ratio of longitudinal reinforcement, type and ratio of transverse reinforcement and beam effective depth. Moreover, a 3-D nonlinear finite element model (FEM) was constructed to simulate the behaviour of FRP-RC continuous beams. The model was verified against the experimental results and validated against test results from previous studies. Then, the verified/validated model was used to conduct a parametric study to investigate the effect of a wide range of the parameters on the shear behaviour of GFRP-RC beams. The experimental and FEM results showed that shear-critical GFRP-RC continuous beams exhibited moment redistribution. Also, it was observed that increasing the concrete strength and the longitudinal reinforcement ratio increased the shear strength significantly. Moreover, the presence of GFRP stirrups significantly enhanced the shear strength of the tested beams. Regarding the size effect, test results showed that there was adverse or no size effect on the shear strength of GFRP-RC continuous beams when they failed in the interior shear span while beams failed in the exterior shear span exhibited clear size effect. Furthermore, a comparison between the test results and the provisions of the available models and FRP standards and design guidelines in North America revealed that these design provisions can be safely applied to continuous beams.
February 2016

Concrete is by far the most widely used construction material worldwide in terms of volume, and so has a huge impact on the environment, with consequences for sustainable development. Portland cement is one of the most energy-intensive materials of construction, and is responsible for some emissions of carbon dioxide — the main greenhouse gas causing global warming. Efforts are being made in the construction industry to address these by utilising supplementary materials and developing alternative binders in concrete; the application of geopolymer technology is one such alternative. Indeed, geopolymers have emerged as novel engineering materials with considerable promise as binders in the manufacture of concrete. Apart from their known technical attributes, such as superior chemical and mechanical properties, geopolymers also have a smaller greenhouse footprint than Portland cement binders.
Research on the development, manufacture, behaviour and applications of low calcium fly ash-based geopolymer concrete has been carried out at Curtin University of Technology since 2001. Past studies of the structural behaviour of reinforced fly ash-based geopolymer concrete members have covered the flexural behaviour of members. Further studies are needed to investigate other aspects of the structural behaviour of geopolymer concrete. Design for both shear and bond are important in reinforced concrete structures. Adequate shear resistance in reinforced concrete members is essential to prevent shear failures which are brittle in nature. The performance of reinforced concrete structures depends on sufficient bond between concrete and reinforcing steel. The present research therefore focuses on the shear and bond behaviour of reinforced low calcium fly ash-based geopolymer concrete beams.
For the study of shear behaviour of geopolymer concrete beams, a total of nine beam specimens were cast. The beams were 200 mm x 300 mm in cross section with an effective length of 1680 mm. The longitudinal tensile reinforcement ratios were 1.74%, 2.32% and 3.14%. The behaviour of reinforced geopolymer concrete beams failing in shear, including the failure modes and crack patterns, were found to be similar to those observed in reinforced Portland cement concrete beams. Good correlation of test-to-prediction value was obtained using VecTor2 Program incorporating the Disturbed Stress Field Model proposed by Vecchio (2000). An average test-to-prediction ratio of 1.08 and a coefficient of variation of 8.3% were obtained using this model. It was also found that the methods of calculations, including code provisions, used in the case of reinforced Portland cement concrete beams are applicable for predicting the shear strength of reinforced geopolymer concrete beams.
For the study of bond behaviour of geopolymer concrete beams, the experimental program included manufacturing and testing twelve tensile lap-spliced beam specimens. No transverse reinforcement was provided in the splice region. The beams were 200 mm wide, 300 mm deep and 2500 mm long. The effect of concrete cover, bar diameter, splice length and concrete compressive strength on bond strength were studied. The failure mode and crack patterns observed for reinforced geopolymer concrete beams were similar to those reported in the literature for reinforced Portland cement beams. The bond strength of geopolymer concrete was observed to be closely related to the tensile strength of geopolymer concrete. Good correlation of test bond strength with predictions from the analytical model proposed by Canbay and Frosch (2005) were obtained when using the actual tensile strength of geopolymer concrete. The average ratio of test bond strength to predicted bond strength was 1.0 with a coefficient of variation of 15.21%. It was found that the design provision and analytical models used for predicting bond strength of lapsplices in reinforced Portland cement concrete are applicable to reinforced geopolymer concrete beams.

Corrosion of steel reinforcement is a major cause of deterioration in reinforced concrete structures especially those exposed to harsh environmental conditions such as bridges, concrete pavements, and parking garages. The climatic conditions may have a hand in accelerating the corrosion process when large amounts of salts are used for ice removal during winter season. These conditions normally accelerate the need of costly repairs and may lead, ultimately, to catastrophic failure. Therefore, using the non-corrodible fibre-reinforced polymer (FRP) materials as an alternative reinforcement in prestressed and reinforced concrete structures is becoming a more accepted practice in structural members subjected to severe environmental exposure. This, in turn, eliminates the potential of corrosion and the associated deterioration. Stirrups for shear reinforcement normally enclose the longitudinal reinforcement and are thus the closest reinforcement to the outer concrete surface. Consequently, they are more susceptible to severe environmental conditions and may be subjected to related deterioration, which reduces the service life of the structure. Thus, replacing the conventional stirrups with the non-corrodible FRP ones is a promising aspect to provide more protection for structural members subjected to severe environmental exposure. However, from the design point of view, the direct replacement of steel with FRP bars is not possible due to various differences in the mechanical and physical properties of the FRP materials compared to steel. These differences include higher tensile strength, lower modulus of elasticity, different bond characteristics, and absence of a yielding plateau in the stress-strain relationships of FRP materials. Moreover, the use of FRP as shear reinforcement (stirrups) for concrete members has not been sufficiently explored to provide a rational model and satisfactory guidelines to predict the shear strength of concrete members reinforced with such type of stirrups. An experimental program to investigate the structural performance of FRP stirrups as shear reinforcement for concrete beams was conducted. The experimental program included seven large-scale T-beams reinforced with FRP and steel stirrups. Three beams were reinforced with CFRP stirrups, three beams reinforced with GFRP stirrups, and one beam reinforced with steel stirrups. The geometry of the T-beam was selected to simulate the New England Bulb Tee Beam (NEBT) that is being used by the Ministry of Transportation of Québec (MTQ), Canada. The beams were 7.0 m long with a T-shaped cross section measuring a total height of 700 mm, web width of 180 mm, flange width of 750 mm, and flange thickness of 85 mm. The large-scale T-beams were constructed using normal-strength concrete and tested in four-point bending over a clear span of 6.0 m till failure to investigate the modes of failure and the ultimate capacity of the FRP stirrups in beam action. The test variables considered in this investigation were the material of the stirrups, shear reinforcement ratio, and stirrup spacing. The specimens were designed to fail in shear to utilize the full capacity of the FRP stirrups. Six beams failed in shear due to FRP (carbon and glass) stirrup rupture or steel stirrup yielding. The seventh beam, reinforced with CFRP stirrups spaced at d /4, failed in flexure due to yielding of the longitudinal reinforcement followed by crushing of concrete. The effects of the different test parameters on the shear behaviour of the concrete beams reinforced with FRP stirrups were presented and discussed. The test results contributed to amending the shear provisions incorporated in the Canadian Highway Bridge Design Code (CAN/CSA-S6) and the updated provisions were approved in the CSA-S6-Addendum (CSA 2009). An analytical investigation was conducted to evaluate the validity and accuracy of available FRP codes and guidelines in Japan, Europe, and North America. The predictions of the codes and the guidelines were verified against the results of the tested beams as well as 24 other beams reinforced with FRP stirrups from the literature. The tested beams were also analysed using various shear theories including the modified compression field theory (MCFT), the shear friction model (SFM), and the unified shear strength model (USSM). A simple equation for predicting the shear crack width in concrete beams reinforced with FRP stirrups is proposed and verified against the experimentally measured values.

A study of the response of eight full-scale deep beams was carried out at McGill University. Four beams were tested by Li (2003) and this thesis reports on the testing of the remaining four beams. The deep beams reported in this thesis were 2000 mm long by 400 mm thick. Two beams had an overall depth of 520 mm and the other two beams had an overall depth of 810 mm. Two beams were reinforced with main tension tie reinforcement only, while the other two contained both vertical and horizontal uniformly distributed reinforcement.
These beams were tested under concentrated load to investigate the influence of span-to-depth ratio and the influence of uniformly distributed horizontal and vertical reinforcement. The presence of uniformly distributed steel resulted in higher capacities, better crack control and also served to control bond splitting failures near the supports. Four approaches were used to predict the capacities: a plane-section model, a simplified strut-and-tie model, a model based on the 1996 FIP Recommendations and a refined strut-and-tie model. The 1996 FIP (Federation Internationale de la Precontrainte) Recommendations gave conservative predictions suitable for design. The refined strut-and-tie model gave the most accurate predictions due to the fact that this approach accounted for the contributions of both the horizontal and vertical uniformly distributed reinforcement in the strut-and-tie model.

The purpose of this research program was to study the behaviour of full-scale deep beams with realistic reinforcement details. In the overall research program, a total of eight deep beams were tested. A companion study by Li (2003) presents the results of four of these beams. This research examines the other four beams, two without uniformly distributed crack control reinforcement and two with distributed horizontal and vertical reinforcement. The specimens' dimensions were 2000 mm long and 400 mm thick, with two specimens having heights of 1160 mm and the other two heights of 1840 mm. The specimens were loaded with a central loading plate 300 mm long and 400 mm wide. The end bearing plates were 250 mm long and 400 mm wide. All specimens contained seven 15M bars forming the main tension tie reinforcement.
The test results provided information on the influence of the uniformly distributed reinforcement and the crack and strain development up to failure. The ductility of the specimens containing only the main tension ties was limited due to the formation of splitting cracks along the anchorages of the main tension ties during the later stages of testing. The uniformly distributed reinforcement provided additional tension ties that increased the capacity and the ductility. Strut-and-tie models were developed to predict the capacities. The FIP Recommendations (FIP 1996) were used to determine the contributions of the two major mechanisms, direct strut action and indirect strut action. This approach gave very conservative strength predictions. More refined strut-and-tie models were developed for the specimens with uniformly distributed reinforcement. These refined models gave more accurate predictions of the capacities of the deep beams.

Thesis (Ph.D) -- University of Western Sydney, 2006.
A thesis submitted to the University of Western Sydney, College of Health and Science, School of Engineering, in fulfilment of the requirements for the degree of Doctor of Philosophy. Includes bibliographical references.

Epoxy bonded fibre reinforced polymer (FRP) composites are widely used for the retrofit of ailing reinforced concrete structures, for both shear and flexure. This technology provides unique features compared with conventional retrofitting systems. Among these FRP has good corrosion resistance, lightweight and excellent mechanical properties. Furthermore, the manual lay-up system allows using the FRP reinforcements to any member’s shape. A significant amount of research has been carried out to understand the shear behaviour of normal weight concrete (NWC) members strengthened with FRP composite. Increasing interfacial (shear) and normal stresses with increasing plastic deformation lead to FRP debonding and/or FRP rupture failures. The response of strengthened concrete members subject to load is governed by the bond strength and the material characteristics of the epoxy bonded FRP reinforcement and the concrete. However, lightweight concrete (LWC) beams, which use Pulverised Fuel Ash (Lytag) instead of normal aggregates, retrofitted to increase shear capacity with epoxy bonded FRP have not been studied comprehensively to understand the characteristics of FRP/ lightweight concrete joining and the shear resisting mechanism. This study comprises of experimental, numerical and analytical investigations of the interface behaviour between carbon fibre reinforced polymer (CFRP) reinforcement and lightweight and normal weight concrete. In addition, the shear behaviour and failure modes of LWAC and NWAC beams is studied. The influence of various variables on the response of the CFRP/lightweight concrete joint and the shear response of reinforced concrete beams are examined by testing large numbers of the experimental series. Three-dimensional non-linear finite element and mathematical models are employed to study the response of the CFRP-to-lightweight concrete interface and the FRP contribution to the shear resistance of lightweight concrete beams have been proposed in this study. Proposed finite element models and relationships were compared with experimental results. The results of the finite element and analytical models demonstrated the capability of these models in predicting the interface behaviour of lightweight concrete/FRP joints and the shear strength gained due to CFRP reinforcement used to retrofit lightweight concrete beams in shear.

Ultra-high performance concrete (UHPC) is a new type of concrete developed by selecting the particle sizes and gradation in the nano- and micro-scales targeting the highest possible packing. The resulting concrete with very high density is called UHPC. UHPC has very low permeability and hence it is very highly durable compared to traditional or high performance concrete (HPC). Micro reinforcement of UHPC by random distributed steel-synthetic fibers results in superior mechanical properties such as very high compressive and tensile strengths, high ductility, and high fatigue resistance. The material selection and early age curing processes, use of fiber reinforcement, and very high quality in production resulted in a very high initial cost of UHPC structures. In order to enable the mass production and cost effective use of the material, performance based design and optimization of UHPC structural members are required. This study is part of an NRC Canada research project to develop innovative, cost effective, and sustainable bridge structural systems using UHPC and other innovative materials. In this study, the estimation of shear and flexural capacities using the available approaches of international design guidelines of UHPC structures are comprehensively compared to a proposed truss models, linear and nonlinear finite element models. Several design trials intended to allow for an optimized use of the materials and a maximum load capacity was conducted for simply supported beams with one or two external loads, and having rectangular or I cross sections. Linear and non-linear finite element models are developed and their results were compared to the available international design recommendations. Truss models are proposed to simplify the stress analysis in the shear zone of the prestressed UHPC beams. It is found that prestressed UHPC I-beam section gives the highest possible load capacity with minimum use of materials. The study shows that for the case of no stirrups, massive flexure and shear cracks initiate and propagate suddenly where a diagonal shear crack is fully developed and sudden collapse may expected. The proposed truss model gives very good match to nonlinear finite element analysis results for almost all the truss members. The results are significantly improved when additional struts are considered for both cases of beams with or without shear reinforcement. The study shows the importance of future experimental investigatinons to calibrate the proposed models.

[Abstract]Over the last few decades, there has been a rapid increase in the volume and weight of heavy vehicles using national road networks. More than half of the bridges around the world are over forty years old. The deterioration of these existing bridges due to increased traffic loading, progressive structural aging, and reinforcement corrosion from severe environmental conditions has become a major problem in most countries. Several techniques have been used to strengthen these structures around the world. External post-tensioning is one of the widely used strengthening techniques in many countries due to its advantages over other methods. Furthermore, flexural strengthening using external post-tensioning has become a well established technique over the past few decades. However, when external post-tensioning is used to strengthen shear damaged reinforced concrete members, unlike flexural damage, the efficiency is significantly reduced by existing shear cracks.This research study was carried out to investigate the behaviour of reinforced concrete beams with existing shear cracks when strengthened by external means. The study consists of two parts: experimental investigations of reinforced concrete beams with different parameters and numerical analysis of reinforced concrete beams usingsimplified theoretical formulation and finite element modelling.To study the behaviour of shear damaged concrete beams, two different strengthening techniques, namely external post-tensioning and external clamping, were used. In addition to the strengthening, the effect of cracks on the behaviour of reinforced concrete beams was investigated by repairing such cracks using epoxy resin injection. Experimental results showed that existing shear cracks have a substantial effect on the member capacity when strengthened by external posttensioning. Although there are concerns about the practical applications of externalclamping, the experimental results suggest that external clamping could be a more effective technique than external post-tensioning to reduce the effect of existing shear cracks on the behaviour of concrete beams. Furthermore, proper repair of the shear cracks could significantly reduce their impact.In the numerical analysis, a simplified mathematical approach was developed to estimate the capacity of shear damaged reinforced concrete beam by expanding themodified compression field theory (MCFT). In addition to the simplified theoretical formulation, a finite element model was developed using the commercial finite element package, Abaqus. Comparison between the predicted behaviour using finite element analysis (FEA) and the experimental data illustrated that the developed finite element model could be used as a reliable tool to estimate the capacity of shear damaged reinforced concrete beams. A parametric study was conducted to investigate the effect of different parameters such as concrete strength, amount of shear reinforcement and crack width, using the developed finite element model. From the numerical study, it was concluded that the simplified approach developedin this study can be used as a reliable and conservative technique to predict the member capacity of a cracked reinforced concrete beam strengthened by external means. Furthermore, the parametric study showed that crack width is the most sensitive parameter that affects the capacity of a cracked beam strengthened by external post-tensioning.Based on this research study it can be concluded that existing shear cracks have a substantial effect on the behaviour of reinforced concrete beams strengthened byexternal post-tensioning. The simplified mathematical approach developed in this study can be used to estimate the capacity of such beams.

This study investigates the shear behaviour of corrosion-damaged reinforced concrete Tbeams repaired with fibre reinforced polymer (FRP) systems. Nine beams with different corrosion levels (0% (uncorroded), 7% and 12%) and different strengthening methods were tested. Both the embedded Carbon-FRP rods and externally bonded Carbon-FRP sheets were effective in enhancing the shear strength of tested beams. The test beams were modelled using nonlinear three dimensional half models in the finite element (FE) package TNO Diana. The shear force capacity, shear force-deflection graphs and crack patterns at failure were used to validate the FE models. Reasonable agreement was obtained between the experimental and numerical results. A parametric study investigating the effect of concrete strength, steel-to-CFRP shear reinforcement ratio and shear span-to-effective depth ratio was carried out. The FE predictions suggest that the embedded CFRP shear contribution decreases with the increase in steel-to-CFRP shear reinforcement ratio and shear span-to-effective depth ratio. Finally, the FE predictions were compared with the predictions of Concrete Society TR55 design guidance. The results suggest that TR55 overestimates the shear strength enhancement offered by embedded CFRP rods.

Several predictive equations and design guidelines are currently available to estimate the total deformation of FRP reinforced concrete members. Although existing approaches can adequately estimate deflections up to service load, however, can also largely underestimate deflections at load levels beyond service. The larger-than expected deflections can be partly attributed to the stiffness degradation caused by the shear-flexure interaction and the change in the stiffness of the load carrying mechanisms. Although studies dealing with the shear behaviour of FRP reinforced concrete beams are currently available in the literature, these tend to focus primarily on the development of models to estimate ultimate shear strength rather than examine the effect of the FRP reinforcement on overall deformation behaviour. An experimental programme was designed to investigate the behaviour of FRP RC beams subjected to shear dominated actions, with a particular focus on their deformation behaviour. Six tests were carried out in two phases on three beams reinforced with FRP flexural and shear reinforcement. All specimens were tested in four point bending and two different shear span-to-depth ratios were examined, namely 3.5 and 2.8. Two different shear reinforcement ratios, 0.5% and 0.27%, were used to reinforce the two shear spans of each of the tested beams to examine the contribution of transverse reinforcement to the deformation behaviour. An analytical framework, based on a non-linear cross section analysis, was developed to perform load deformation analyses of RC beams. The framework was then extended to enable the use of different material models and to account for the effects of shear induced phenomena on overall deflections. On the basis of the results obtained from the experimental programme and the analytical framework, a new approach is proposed to model the development of a shear resisting truss mechanism and estimate the inclination of the compression struts. This concept is used to estimate shear induced deformation and improve existing models. Comparisons are carried out between the results provided by the analytical model and the experimental data, along with the load deflection responses estimated according to existing design guidelines and other models from current literature. This new model allows the inclusion of shear-induced deflection throughout the load history of the element and yields more accurate results.

Partially Prestressed Concrete (PPC) is an intermediate design approach between reinforced and totally prestressed concrete, that enables controlled cracks in service phase. Conversely, totally prestressed concrete is design to prevent cracks in service. This design strategy can be useful for structural optimization, as allows for more freedom in the variation of stiffness, crack opening, stress level and resistance. This technique has been studied during the past decades. However, its extensive use has been limited due to the lack of methodologies to control the crack width. This thesis aims to analyse the behaviour of PPC under flexural and shear forces. In this research, the behaviour of PPC elements in bending and shear is investigated through an an experimental campaign of sixteen tests. The specimens were design to represent the webs of a girder box bridge, hence the I section of the beams. From the sixteen tests, twelve studied the shear behaviour of PPC beams and the influence of web width, prestress ratio, stirrup ratio and lay out. The remaining tests were four-point bending tests. The aim of these tests was to evaluate the flexural behaviour at service and failure by changing the prestress and longitudinal reinforcement ratios. For each test, the loading protocol performed cyclic loads to analyse the evolution of the behaviour of the specimens at service. The cycles presented three steps corresponding to quasi-permanent, frequent and characteristic load level. Each step was used to analyse and compare the evolution of the main parameters that characterise the behaviour of the beams. After the cycles, the load was monotonically increased until failure. Several models have been presented to explain the shear resistance mechanism for sections with flanges, with very different results. The Compression Chord Capacity Model (CCCM) presented the best predictions for this experimental campaign. A photogrammetric technique was developed to analyse the shear crack pattern. This technique obtains from the pictures the crack spacing, the crack angle and the crack width. With this tool, an equation to predict the cot 𝜃� at service and failure was obtained. The equation relates the angle of the cracks with the ratio between compression due to prestress and tensile strength and the ratio of stirrups. This technique allowed to obtain the influence of the reinforcements over the crack shear width. A model to predict the average shear crack width in service was developed using the average strain of the stirrups, the experimental crack spacing and the angle of the cracks. Strains were calculated taking into account the shear contribution of the stirrups. From the experimental results, it was evidenced that in the shear tests at service, the strains in the stirrups were over the yielding threshold. Therefore, the shear cracks were large. Meanwhile the strains in the four-point bending tests only reached the yielding level in failure, being stable for the service part of the test.
El Hormigón Parcialmente Pretensado (HPP) es una estrategia de diseño intermedia entre el hormigón armado y el pretensado total el cual permite la fisuración controlada en fase de servicio; en contraposición, el hormigón totalmente pretensado se dimensiona para evitar la fisuración en servicio. Esta estrategia de diseño puede ser de gran utilidad para la optimización estructural, ya que permite una variación gradual en la rigidez, apertura de fisura, niveles tensionales y resistencia. Esta técnica ha sido estudiada durante décadas; sin embargo, su uso extensivo se ha visto limitado por la falta de metodologías para controlar el ancho de fisura. Esta Tesis busca analizar el comportamiento del HPP sometido a esfuerzos de flexión y cortante. En esta investigación, se estudia el comportamiento de elementos de hormigón parcialmente pretensado, a flexión y cortante, mediante un estudio experimental de dieciséis ensayos. Los especímenes fueron diseñados para representar las almas de puentes en cajón, de ahí la sección en doble‐T de las vigas. De los dieciséis ensayos, doce estudiaron el comportamiento a cortante del HPP y la influencia del ancho del alma, el grado de pretensado, la cuantía de armadura transversal y el trazado del pretensado. El resto de casos fueron ensayados a flexión. El objetivo de estos últimos casos fue evaluar el comportamiento a flexión, en servicio y rotura, con diferentes cuantías de armadura pasiva y activa. Para analizar el comportamiento en servicio, el protocolo de carga constaba de ciclos de carga. Los ciclos recorrían tres niveles de carga, casi‐permanente, frecuente y característico. En cada nivel se analizó y comparó la evolución de los principales parámetros para caracterizar el comportamiento de las vigas. Después de los ciclos, se aplicó una carga monotónica hasta rotura. Se analiza la bondad de diferentes modelos de resistencia a corte para el caso de elementos pretensados con alas comprimidas. De entre los diferentes modelos estudiados, el modelo de “Capacidad de Cordón Comprimido” o “Compression Chord Capacity Model” (CCCM) presentó las mejores predicciones para esta campaña experimental. Así mismo, se desarrolló una técnica fotogramétrica para analizar el patrón de la fisuración a cortante. Esta técnica permite obtener de las imágenes la separación entre fisuras, el ángulo de las fisuras y el ancho de fisura. Esta herramienta permitió generar una ecuación para predecir la cot 𝜃 en servicio y rotura. La ecuación relaciona el ángulo de las fisuras con las tensiones de compresión en el hormigón por el pretensado y su resistencia a tracción y la cuantía de armadura transversal. Con esta técnica se obtuvo la influencia entre los estribos y el ancho de las fisuras a cortante. Posteriormente, se propuso un modelo para predecir el ancho medio a cortante en servicio, usando la deformación media de los estribos, la separación entre fisuras y la inclinación de las fisuras. Las deformaciones se calcularon teniendo en cuenta la contribución a cortante de los estribos. De los resultados experimentales se concluye que, para los ensayos a cortante, las deformaciones en los estribos superan la deformación de plastificación en servicio. Lo que conlleva a grandes oberturas de fisura. Mientras que las deformaciones en la armadura longitudinal de los ensayos a flexión solo llegan a la deformación de plastificación en rotura, manteniendo deformaciones controladas en servicio.

O comportamento mecânico de vigas em alvenaria estrutural submetidas ao cisalhamento é abordado de forma aprofundada neste trabalho. São apresentados neste estudo um extensivo levantamento bibliográfico, o qual estabelece um panorama sobre o tema, um programa experimental com ensaios de caracterização do material alvenaria e de vigas em escala natural e um estudo numérico das vigas ensaiadas em laboratório. Na etapa de caracterização dos materiais o comportamento compósito da alvenaria é analisado por meio de prismas submetidos à compressão em duas direções ortogonais, normal e paralela à junta. Para o estudo das vigas são realizados trinta e sete ensaios, nos quais são avaliadas as influências da geometria, das taxas de armaduras e da relação a/d (em que a é a distância da carga aplicada até o apoio e d é a altura útil) na capacidade resistente ao cisalhamento. Posteriormente, é realizada a modelagem numérica através do software DIANA® com o propósito de complementar as análises dos ensaios. A partir dos resultados experimentais e numéricos pôde-se concluir que, com exceção das vigas com armaduras longitudinais de 10 mm de diâmetro, os demais modelos atingiram a ruína por cisalhamento, devido à ausência de estribos ou pela sua insuficiência. O aumento da taxa de armadura longitudinal de 0,45 para 1,18% resultou em um incremento de 18,4% na resistência ao cisalhamento convencional. Para as duas geometrias (vigas com duas e três fiadas) e as duas relações a/d (0,77 e 1,72), constatou-se que não há uma melhora significativa na capacidade resistente quando a taxa de armadura transversal é aumentada de 0,05 para 0,07%. Os mecanismos resistentes, como o efeito de pino, foram efetivos na resistência dos modelos. Por fim, as análises numéricas reproduziram de forma satisfatória os experimentos, tanto no que diz respeito ao comportamento pré e pós-pico quanto na previsão da força última.
This work is an in depth study about the mechanical behaviour of masonry beams subjected to shear forces. An extensive literature review, which establishes a panorama on the subject, an experimental program considering material characterization and full scale beams tests and a numerical study for the tested beams are presented. For the beams, thirty seven tests are carried out in which the influence of geometry, reinforcements ratio and a/d ratio (where a is the distance from the load to adjacent support and d is the effective depth) on the shear strength are evaluated. Computational modelling is performed using the DIANA® software in order to complement the experimental results. From the experimental and numerical results it was possible to conclude that, except for beams with 10 mm diameter steel bar, the other models failed in shear, due to the absence of stirrups or their insufficiency. An increase in longitudinal reinforcement ratio from 0,45 to 1,18% improved the theoretical shear strength in 18,4%. For the beams with two and three courses and for a/d ratios 0,77 and 1,72 it was found that there is no significant improvement on the load capacity when the transverse reinforcement ratio is increased from 0,05 to 0,07%. Shear strength mechanisms, such as the dowel action, were effective in the models load capacity. Finally, the numerical analyzes satisfactorily reproduced the experiments, regarding to the pre and post-peak behaviour and in the prediction of the ultimate load.

This research study examined the effect of corrosion of web reinforcement (stirrups) on the shear behaviour of slender reinforced concrete (RC) beams. The experimental program consisted of seventeen slender shear-critical RC beams: five uncorroded and twelve corroded beams. The test variables included: 1) corrosion level (0%, 7.5% and 15%); 2) type of stirrups (smooth and deformed); 3) stirrup diameter (D6, D12 and 10M); 4) stirrups spacing (100mm and 200mm); and 5) the presence of CFRP repair. The corroded beams had their stirrups subjected to corrosion using an accelerated corrosion technique and the mass loss in the stirrups was estimated based on Faraday’s law. All of the beams were monotonically tested to failure in three point bending. The corrosion cracks formed were parallel to the locations of stirrups as evidence of the corrosion damage in the corroded beams. The maximum decrease in the ultimate shear strength ranged from 11% to 14.4% for beams with high corrosion level of 15.6% mass loss. At a low corrosion level (4.39% mass loss), the shear strength of beams with smooth stirrups increased up to 35% due to the enhancement of shear friction at the concrete-corroded stirrups interface. The stiffness of the corroded beams was enhanced in comparison to the control beams. The ultimate deflection of the corroded beams was decreased up to 25% in comparison to the control beams. The CFRP repair increased the shear strength by 36% and improved the overall stiffness by 39% in comparison to the corroded unrepaired beams. All of the unrepaired beams failed in diagonal tension splitting, while the CFRP repaired corroded beams failed in diagonal tension splitting in addition to debonding of the FRP or concrete cover delamination. The actual corrosion mass loss results were in good correlation with Faraday’s law for the D12 and 10M stirrups. Poor correlation between actual and estimated mass loss was obtained for D6 smooth stirrups, possibly due to errors in the impressed corrosion. iv The analytical model used the modified compression field theory (MCFT) to predict the shear strength of uncorroded and corroded slender RC beams. In the corroded beams, two reduction factors were added to the MCFT model including the mass loss factor and the effective web width. Predictions based on the model revealed that the control beams gave a very good correlation with the ratio of experimental to predicted values that ranged from 0.94 to 1.02. On other hand, the ratio of experimental to predicted strength in the corroded beams ranged between1.06 to 1.4. The poor correlations were obtained for the beams with the D6 smooth stirrups. This study demonstrates that corrosion of web reinforcement can have a detrimental effect on the shear strength and ductility of slender shear-critical RC beams. The experimental results and analytical approach will be very useful for practicing engineers and researchers dealing with corrosion damage in slender RC members.

Corrosion of reinforcing steel is a major problem facing infrastructures owners with billions of dollars spent in repairing our aging infrastructure. One of the first steps in the repair process is to quantify the strength degradation in a reinforced concrete element caused by the corrosion of reinforcing steel. An understanding of the forces involved in the load carrying mechanisms is imperative; the transfer of shear forces in reinforced concrete beams is one of these load carrying mechanisms. The shear transfer mechanism is different near the end of beams, adjacent to point loads, and near changes in cross section. These regions are known as disturbed regions. Structural engineers have a good understanding of the shear transfer mechanism in disturbed regions. However, the effects of corroded shear reinforcement in these regions have not been widely investigated. The current study is comprised of an experimental program and analytical strut and tie modeling aimed at quantifying the strength reduction that occurs in disturbed regions of reinforced concrete beams with corroded shear reinforcement. The feasibility of strengthening a beam with dry lay-up carbon fibre reinforced polymer (CFRP) to repair the damage caused by corrosion of the shear reinforcement was also investigated. In the experimental study, a total of 16 reinforced concrete beams were cast. The specimens were 350 mm deep, 125 mm wide and 1850 mm long. Three shear-span to depth ratios (1.0, 1.5, 2.0) were selected. Each specimen was reinforced in flexure with two 25M bars and the shear reinforcement was 10M spaced at 150 mm on centre. The specimens were corroded for 21 days, 60 days, and 120 days corresponding to low, medium, and high corrosion levels. In addition, three specimens were constructed without shear reinforcement in the shear-span in order to compare the results from the corroded specimens. One specimen was also corroded to a high level and repaired with dry lay-up CFRP. The specimens were corroded using an accelerated corrosion technique. There was evidence of cracking of the cover concrete in all specimens, and in the more severely corroded specimens delamination of the cover concrete was recorded. The stiffness of the corroded specimens was less than their corresponding control specimen, and a strength reduction was evident in most specimens. The maximum recorded strength reduction was 52% compared to the companion uncorroded specimen. It was revealed that a more critical case occurs when the corroded shear reinforcement was shifted during placement or was inclined closer to the direction of the compressive force flow. Also, it was observed that the corroded shear reinforcement still provides limited ductility in comparison to the un-corroded reinforcement. A strut and tie model was developed based on the experiments to explain the behaviour of disturbed regions with corroded shear reinforcement. The model consisted of direct and indirect struts. The effects of corrosion were expressed in terms of a reduction in the stirrup cross-section, a reduction of compressive strength due to corrosion cracking, and a reduction in the concrete cross section width. It was hypothesized that the corrosion crack width influences the concrete compressive strength in the strut; consequently, a mathematical model was developed that related the reduction in concrete compressive strength with corrosion crack width. Also, a relationship between reinforcing steel mass loss and corrosion crack width was utilized from the published literature. An effective cross section width was obtained by reducing the width by the damaged concrete cover. The results from these models were input into a strut and tie model as a reduction in concrete compressive strength. The output from the strut and tie model was the ultimate shear strength of the specimen. The developed models were compared with a model from the literature and compared with the experimental results. The major contribution of this research is to allow designers to analyze disturbed regions with corroded shear reinforcement and determine the strength degradation; subsequently, one can determine what strengthening procedure would be most appropriate.

This thesis discusses the results of an experimental program designed to investigate the effect of corrosion on the behaviour of shear critical reinforced concrete (RC) beams. The results of twenty RC beams (ten deep beams and ten slender beams) are described and discussed. The test variables included: corrosion level (2.5%, 5% and 7.5%) and existence of stirrups (beams without stirrups and beams with stirrups). The feasibility of repairing the corroded shear critical RC beams with CFRP laminates was also investigated. Sixteen specimens were corroded using an accelerated corrosion technique whereas four specimens acted as control un-corroded. Following the corrosion phase, all specimens were tested to failure under three point bending. Test results revealed that the corrosion does not adversely affect the behaviour of shear critical RC beams rather it improves their behaviour. It was found that corrosion changed the failure mode of the corroded beams. The control un-corroded deep beams (beams with and without stirrups) failed in shear-compression failure whereas corroded deep beams (beams with and without stirrups) failed by splitting of the compression strut. The control un-corroded slender beams (beams with and without stirrups) failed in diagonal tension failure whereas the corroded slender beams failed in anchorage failure (beams without stirrups) and flexural failure (beams with stirrups). The analysis of the results showed that corrosion changed the load transfer mechanism and the change of failure mode was associated with the mechanism. The load transfer mechanism changed from a combination of beam and arch action in the control un-corroded deep beams to pure arch action in the corroded deep beams. The load transfer mechanism changed from pure beam action in the control un-corroded slender beams to pure arch action in the corroded slender beams. Two strut and tie models are proposed: one for corroded deep beams and one for corroded slender beams. The ultimate loads of the corroded beams were predicted using these struts and tie models and compared with the experimental results. A very good correlation was found between predicted and experimental results.

No
This paper presents a numerical investigation into the behaviour of headed shear stud in composite beams with profiled metal decking. A three-dimensional finite element model was developed using general purpose finite element program ABAQUS to study the behaviour of through-deck welded shear stud in the composite slabs with trapezoidal deck ribs oriented perpendicular to the beam. Both static and dynamic procedures were investigated using Drucker Prager model and Concrete Damaged Plasticity model respectively. In the dynamic procedure using ABAQUS/Explicit, the push test specimens were loaded slowly to eliminate significant inertia effects to obtain a static solution. The capacity of shear connector, load-slip behaviour and failure modes were predicted and validated against experimental results. The delamination of the profiled decking from concrete slab was captured in the numerical analysis which was observed in the experiments. ABAQUS/Explicit was found to be particularly suitable for modelling post-failure behaviour and the contact interaction between profiled decking and concrete slabs. It is concluded that this model represents the true behaviour of the headed shear stud in composite beams with profiled decking in terms of the shear connection capacity, load-slip behaviour and failure modes.

No
This paper presents a numerical investigation into the behaviour of headed shear stud in composite beams with profiled metal decking. A three-dimensional finite element model was developed using general purpose finite element program ABAQUS to study the behaviour of through-deck welded shear stud in the composite slabs with trapezoidal deck ribs oriented perpendicular to the beam. Both static and dynamic procedures were investigated using Drucker Prager model and Concrete Damaged Plasticity model respectively. In the dynamic procedure using ABAQUS/Explicit, the push test specimens were loaded slowly to eliminate significant inertia effects to obtain a static solution. The capacity of shear connector, load-slip behaviour and failure modes were predicted and validated against experimental results. The delamination of the profiled decking from concrete slab was captured in the numerical analysis which was observed in the experiments. ABAQUS/Explicit was found to be particularly suitable for modelling post-failure behaviour and the contact interaction between profiled decking and concrete slabs. It is concluded that this model represents the true behaviour of the headed shear stud in composite beams with profiled decking in terms of the shear connection capacity, load-slip behaviour and failure modes.

This paper presents a numerical investigation into the behaviour of headed shear stud in composite beams with profiled metal decking. A three-dimensional finite element model was developed using general purpose finite element program ABAQUS to study the behaviour of through-deck welded shear stud in the composite slabs with trapezoidal deck ribs oriented perpendicular to the beam. Both static and dynamic procedures were investigated using Drucker Prager model and Concrete Damaged Plasticity model respectively. In the dynamic procedure using ABAQUS/Explicit, the push test specimens were loaded slowly to eliminate significant inertia effects to obtain a static solution. The capacity of shear connector, load-slip behaviour and failure modes were predicted and validated against experimental results. The delamination of the profiled decking from concrete slab was captured in the numerical analysis which was observed in the experiments. ABAQUS/Explicit was found to be particularly suitable for modelling post-failure behaviour and the contact interaction between profiled decking and concrete slabs. It is concluded that this model represents the true behaviour of the headed shear stud in composite beams with profiled decking in terms of the shear connection capacity, load-slip behaviour and failure modes.

This research includes a preliminary study prior to the commencement of the Ph.D. work and three phases of design, construction and testing of three generations of moment-shaped beams. Each phase of the research brought a better understanding of curved beams which follow the shape of the moment diagram. The moment diagram in this study was for simply supported beams supporting a uniformly distributed load as would be the case in the majority of building designs. The original theory for this research can be described as follows: Moment-shaped beams are the natural outcome of a fundamental understanding of stress paths in a horizontal load bearing member. By following these stress paths we may provide materials where required to most efficiently carry the compression and tension stresses to the supports. Allowing stresses to follow their naturally desired paths reduces regions where stresses cross paths called disturbed regions. The outcome of the final phase of this research was the development of the third generation of curved beams with a camber. These beams, designated as Cambered Curve beams (CCBs), exhibited the same behaviour as the rectangular control beam design using CSA-A23.3 up to the serviceability failure of L/360 (12mm). The CCB moment-shaped beams require 20% less concrete and 40% less reinforcing steel (no shear stirrups) to carry the ultimate load which is only 12% less than that carried by the CSA-designed control beam. Due to a closed system of internal forces, the moment-shaped beams remain intact and are able to sustain self weight, even after total failure. A significant part of this research was to modify and verify a FORTRAN-based finite element analysis program: FINIT-Y. This program was reconstructed to analyse a full size beam, and enabled the researcher to model and correctly predict the maximum load, crack pattern and failure mode. This study found that moment-shaped beams with no shear reinforcement have the same stiffness and load carrying capacity as the CSA-designed rectangular control beam with shear reinforcement up to serviceability failure (L/360). The study also found that moment-shaped beams have significantly lower ductility at the ultimate load.

The inclusion of trapezoidal types of steel decking in the shear connection of composite beams has been found to significantly reduce their maximum strength and ductility by causing premature concrete-related failure modes. In order to investigate the complex behaviour and various load-transfer mechanisms that can occur in composite beams incorporating this type of connections, a total of 91 carefully-designed push-out tests were performed. Specific failure modes in conventionally reinforced specimens were initially induced by varying critical parameters. Specimens incorporating specific stud reinforcing devices were subsequently tested to suppress the undesirable failure modes. The concrete reinforcing and stud performance-enhancing devices, which included novel waveform-type reinforcement elements and spiral wire or ring components surrounding individual studs in secondary composite beams and special haunch reinforcement in primary beam applications, significantly delayed the onset and reduced the effect of the premature concrete-related failure modes. Hence, they increased the ultimate strength and ductility of the shear connection. The findings of the small-scale push-out tests were also verified in two full-scale composite beam tests which showed good agreement in shear connection behaviour and failure mode. Most of the design approaches currently used around the world take into account the weakening effect of trapezoidal types of decking by applying a reduction factor to the nominal strength that the same connection would have in a solid slab. From the test results, it is evident that not every shear connection incorporating steel decking, and within the limits of the associated standards, can be classified as ductile. A new and more reliable design approach is proposed which also incorporates the application of the various stud reinforcing devices. The key element of this design approach is to classify the anticipated connection behaviour, in regards to its deformation capacity, into ductile or brittle connections, hence ensuring satisfactory shear connection behaviour where the new types of trapezoidal steel decking are used. A reliability analysis of the new proposal is presented which enables the application of this new approach in accordance with AS 2327.1 (Standards Australia 2003). It is calibrated to provide a reliability index similar to stud applications currently in use. Simple strength reduction factors for the types of trapezoidal steel decking available in Australia are also provided which can be applied to the current solid slab shear connection strength for a fast and simplified design.
Doctor of Philosophy (PhD)

Experiments were conducted to investigate the shear behaviour of large deep beams subjected to uniform load. Six tests were performed on specimens with identical cross sections and reinforcing, but under different loading configurations. Variables included: span, degree of cracking prior to loading, proximity to a disturbed region near a reaction, and type of flexural stress on the loaded face. The findings indicate a specific set of variables resulting in unconservative predictions made using a strut-and-tie model for simply-supported beams subjected to uniform load, confirming and validating recent results by other researchers. A fanning strut model is proposed and is shown to provide more conservative results. The emerging trend of high capacity in continuous uniformly-loaded specimens is supported by the experimental results, as is the high capacity of specimens uniformly-loaded on their flexural tension face. Further, the high strength of specimens with suboptimal crack orientations supports recent experimental work.

Yes
This paper outlines an experiment on a 12 m long composite beam subjected to uniformly distributed loading. Although composite beams are widely used, current Eurocode design guidelines for these types of members can be over-conservative, particularly in relation to the required degree of shear connection. The tested beam comprised a concrete slab supported by profiled metal decking, connected to an asymmetric fabricated steel I-beam using welded shear studs. The specimen was assembled using unpropped construction methods and had a degree of shear connection equal to 33%, significantly lower than the minimum required amount specified in Eurocode 4. A uniformly distributed load was applied to the specimen, which was increased until the failure occurred characterized by yielding of the steel beam. The maximum bending moment of the composite beam obtained from the test was close to the plastic bending resistance according to the Eurocode 4. No concrete crushing or shear stud failure was observed and the end slips exceeded 6 mm, the limit for ductile behaviour in Eurocode 4. The test demonstrated the merits of unpropped construction, which are currently not fully exploited in Eurocode 4. The comparison and analysis suggest that the design limits governing the minimum degree of shear connection might be revised.
RFCS

Ageing infrastructure that is shear deficient and may be at risk of brittle collapse, particularly in seismically active regions, can be economically strengthened using externally bonded fibre-reinforced polymers (FRP). Although many studies have been conducted on small-scale specimens subject to monotonic loading, little experimental data exists for large-scale specimens and those tested under reversed cyclic loading to simulate a seismic event. An experimental study of large-scale (400 mm x 650 mm) beam specimens strengthened in shear with FRP was conducted to examine the effects of reversed cyclic loading and to quantify material shear strength contributions. Testing showed that FRP retrofits were highly effective at improving shear performance and were not adversely affected by reversed cyclic loading prior to the occurrence of flexural yielding. The shear resistance attributed to concrete was found to remain relatively consistent with reversed cyclic loading prior to flexural yielding, after which point concrete strength decay was apparent. The loss of concrete shear resistance directly influenced the rate of FRP straining and the achievable ductility. An analytical model using the Modified Compression Field Theory (MCFT) was developed for externally bonded FRP reinforcement to describe the experimental behaviour and to evaluate the accuracy of current FRP design methods. Failures were accurately modelled when appropriate FRP strain limits were used for the ultimate strength and for the stress transfer capacity across the shear crack. Proposed FRP strain limits were developed considering the strain distribution along the crack plane. In addition, improved strain limits incorporate the effect of rupture failure due to stress concentrations in the FRP wrapped around the beam corners. The proposed FRP formulations offer improved accuracy over the current FRP design methods (CSA S6-06 and ACI 440.2R-08), which suggest a broadly applied maximum strain limit of 0.004 mm/mm, which was determined to be overly conservative for FRP rupture failures.

In composite beam design, headed stud shear connectors are commonly used to transfer longitudinal shear forces across the steel¿concrete interface. Present knowledge of the load¿slip behavior and the shear capacity of the shear stud in composite beam are limited to data obtained from the experimental push-off tests. For this purpose, an effective numerical model using the finite element method to simulate the push-off test was proposed. The model has been validated against test results and compared with data given in the current Code of Practices, i.e., BS5950, EC4, and AISC. Parametric studies using this model were preformed to investigate variations in concrete strength and shear stud diameter. The finite element model provided a better understanding to the different modes of failure observed during experimental testing and hence shear capacity of headed shear studs in solid concrete slabs

No
This paper presents the experimental and numerical investigation into the behaviour of headed shear studs in composite beams with profiled metal deck flooring. A new single-sided horizontal push test arrangement is proposed to evaluate the shear capacity of the headed shear connectors in pairs with metal deck profiled sheeting. The characteristic resistance obtained from the horizontal push test is compared with Eurocode 4. A three-dimensional finite element model was developed using general purpose finite element program ABAQUS/Explicit. The shear connector capacity, load-slip behaviour and failure modes are validated against experimental results and close correlations were obtained.

Concrete deep beams with small shear span-to-depth (a/d) ratios are common elements in structures. However, there are few experimental results on the behaviour of FRP reinforced concrete deep beams and no specific modelling techniques exist in design codes for such members. The objectives of this study were to examine the shear behaviour of FRP reinforced concrete deep beams containing no web reinforcement and to develop a modelling technique. Test results of 12 large-scale specimens are reported where the primary variables included the a/d ratio, reinforcement ratio, member height, and concrete strength. The results showed that an arch mechanism was able to form in FRP reinforced concrete beams having a/d 2.1. A strut and tie modelling procedure adapted from CSA A23.3-04 was capable of accurately predicting the capacity of FRP reinforced concrete deep beams containing no web reinforcement while sectional shear models gave poor, but conservative, predictions.
Structural Engineering

Dissertação de Mestrado Integrado em Engenharia Civil apresentada à Faculdade de Ciências e Tecnologia
Tendo em conta a realidade atual, é importante desenvolver e adotar medidas de sustentabilidade, para não colocar em causa o futuro das gerações futuras. Neste contexto, é conhecido que ao longo dos anos têm-se verificado diversos problemas no uso do cimento Portland normal CPN, tanto na vertente de impactes ambientais associados à sua produção, como nas limitações ao nível do seu desempenho mecânico, mais concretamente na sua durabilidade. Deste modo, é imperativo desenvolver materiais alternativos ao usual CPN. Sendo assim, pretende-se com este documento estudar a viabilidade de um ligante ativado alcalinamente, o metacaulino castanho, quando utilizado de forma estrutural e submetido essencialmente a esforços de corte.O estudo realizado para este documento é de caracter experimental e incide na avaliação do comportamento de vigas geopoliméricas submetidas ao corte. Para tal, desenvolveu-se uma metodologia de ensaio com 6 pontos de aplicação de carga, proporcionando simetricamente duas zonas de estudo submetidas essencialmente ao esforço transverso, reduzindo o efeito do momento fletor em cada zona.A metodologia de ensaio utilizada permitiu obter resultados bastantes satisfatórios. Entre estes, as vigas geopoliméricas demostraram ser mais dúcteis relativamente às vigas constituídas por CPN e exibiram uma degradação gradual da rigidez após a fase elástica. A mistura geopolimérica apresentou boas características de comportamento ao nível dos parâmetros analisados, embora ainda necessite de melhorar alguns aspetos para que possa ser exequível a sua utilização nas obras correntes de engenharia civil.
Given the current situation, it is important to develop and adopt sustainability measures to not jeopardize the future of next generations. In this context, it is known that over the years there have been several problems with the use of ordinary Portland cement OPC, both in terms of environmental impacts associated with its production, as well as in the limitations of its mechanical performance, more specifically its durability. Thus, it is imperative to develop alternative materials to the usual OPC. Therefore, it is intended with this document to study the viability of an alkaline activated binder, the brown metakaolin, when used in a structural way and subjected essentially to shear stresses.The study carried out for this document is experimental and focuses on the evaluation of the behavior of geopolymer beams subjected to shear. For this, a test methodology with 6 points of load application was developed, providing symmetrically two study areas submitted essentially to the shear stress, reducing the effect of the bending moment in each zone. The test methodology used allowed to obtain quite satisfactory results. Among these, the geopolymer beams proved to be more ductile with respect to the beams constituted by OPC and exhibited a gradual degradation of the stiffness after the elastic zone. The geopolymer mixture presented good behavioral characteristics in terms of the analyzed parameters, although some aspects still need to be improved so it could be used in current civil engineering works.
Universidade de Coimbra - Material e equipamento laboratorial utilizado.

[EN] Several efforts have been made in experimental and theoretical research about shear to understand all the variables that influence the phenomenon. Nowadays, however, due to its complexity, the shear performance of structural concrete elements, especially those without any traditional transversal reinforcement, continue with no clear explanation of the problem. Uncertainty about the problem grows when new variables like fibres are incorporated into the shear study. Research works have demonstrated the effectiveness of steel fibre in improving the mechanical properties of concrete elements. Experimental results reveal that steel fibres have proven effective in improving shear resistance, and they confer some concrete elements more ductility. In adequate amounts, steel fibres can completely or partially substitute traditional shear reinforcements. This is why international codes have included some requirements to take into account the action of fibres on the shear response of concrete elements. However, most recommendations and requirements for steel fibre-reinforced concrete (SFRC) were originally created. New fibres with different materials properties and shapes, such as macrosynthetic fibres, are now available on the market. These fibres, some of which are made of polypropylene, are an alternative in the construction industry given their properties and final cost. Initially, polypropylene fibres were used to control shrinkage cracking. Nevertheless, in the last decade the chemical industry has created larger fibres with better surface shapes, which allows polypropylene fibres to meet the requirements of international codes so they can be used in structural elements. Within this framework, the present PhD thesis aims to contribute to knowledge about fibre reinforced concrete (FRC), especially to study the effectiveness of polypropylene fibres when used as shear reinforcement. For this purpose, a literature review of the material, polypropylene fibre-reinforced concrete (PFRC) and its structural applications is first carried out. This study also discusses the parameters that affect the shear behaviour of traditional concrete and FRC. In order to evaluate the effectiveness of polypropylene fibres in shear, three experimental campaigns are presented. Each campaign represents a different level of study. The first corresponds to the material level, where the shear behaviour of PFRC is evaluated by push-off specimens. The second level involves studying shear in real scale elements. For this purpose, shear critical slender beams were manufactured and tested. The last level corresponds to real application of polypropylene fibres to act as shear reinforcement. In this campaign, deep hollow core slabs, with real sections and supports conditions, were tested. At each level, the shear behaviour of PFRC was evaluated against control reinforced concrete specimens, which were also tested during each campaign.
[ES] Varias investigaciones experimentales y teóricas han sido realizadas para entender el comportamiento a cortante de elementos de hormigón y sus variables. Sin embargo, hoy en día debido a la complejidad del tema, el comportamiento a cortante de elementos de hormigón armado y en especial aquellos que no tienen refuerzo transversal, continúan sin tener una explicación clara. Por otro lado, esta complejidad del cortante aumenta cuando nuevas variables, como las fibras, se incorporan al estudio. Investigaciones han demostrado la efectividad de las fibras de acero para mejorar las propiedades mecánicas de hormigón. Según resultados experimentales, la fibra de acero mejora la resistencia cortante y ductilidad de ciertos elementos. Y en cantidades adecuadas, la fibra puede sustituir total o parcialmente los refuerzos tradicionales de cortante. Es así que varios códigos internacionales han incluido requisitos para tener a las fibras en la respuesta estructural de elementos de hormigón. Sin embargo, estos requerimientos se han creado originalmente para el hormigón reforzado con fibra de acero (Steel fibre-reinforced concrete -SFRC). Nuevas fibras con diferentes materiales y formas, como las fibras macro-sintéticas, han sido introducidas en el mercado. Estas fibras, también llamadas fibras de polipropileno o poliolefina, son una alternativa en la construcción debido a su propiedades y costo final. Inicialmente, las fibras de polipropileno eran usadas únicamente en el hormigón para controlar la fisuración por retracción. Sin embargo, en la última década la industria química ha desarrollado fibras más grandes y con mejores prestaciones de adherencia, que permiten a estas fibras cumplir con requisitos para ser utilizadas estructuralmente. En este contexto, la presente tesis pretende ser una contribución al conocimiento sobre el hormigón reforzado con fibras (Fibre-reinforced concrete - FRC), especialmente en la efectividad de las fibras de polipropileno como refuerzo a cortante. Para esto, primero se realiza un estudio bibliográfico del hormigón reforzado con fibra de polipropileno (PFRC) como material y sus aplicaciones estructurales. Este estudio también tratará sobre los parámetros que afectan el comportamiento a cortante del hormigón tradicional y hormigón reforzado con fibras. Para evaluar la efectividad de las fibras de polipropileno en el cortante, se realizarán tres campañas experimentales. Cada campaña representa un nivel de estudio diferente. El primero es a nivel material en donde se evalúa el comportamiento a cortante a través de especímenes tipo Push-off. El segundo nivel, corresponde al estudio del cortante en elementos a escala real. Para esto se fabrican y ensayan vigas esbeltas críticas a cortante. El último nivel corresponde a una aplicación real de fibras de polipropileno actuando como refuerzo cortante. En esta campaña, se fabrican y ensayan placas alveolares de gran canto con secciones y condiciones de apoyos reales.
[CA] Diverses investigacions experimentals i teòriques han estat realitzades per entendre el comportament a tallant d'elements de formigó i les seues variables. No obstant això, hui en dia a causa de la complexitat del tema, el comportament a tallant d'elements de formigó armat i especialment aquells que no tenen reforç transversal, continuen sense tindre una explicació clara. D'altra banda, aquesta complexitat del tallant augmenta quan noves variables, com les fibres, s'incorporen a l'estudi. Investigacions han demostrat l'efectivitat de les fibres d'acer per a millorar les propietats mecàniques del formigó. Segons resultats experimentals, les fibres d'acer milloren la resistència a tallant i la ductilitat de certs elements. A més, en quantitats adequades, les fibres poden substituir total o parcialment els reforços tradicionals de tallant. És així que diversos codis internacionals han inclòs requisits per a tindre amb compte la resposta estructural de les fibres en els elements de formigó. No obstant això, aquests requeriments s'han creat originalment per al formigó reforçat amb fibres d'acer (Steel fibre-reinforced concrete -SFRC). Noves fibres amb diferents materials i formes, com les fibres macro-sintètiques, han estat introduïdes al mercat. Aquestes fibres, també anomenades fibres de polipropilè o poliolefina, són una alternativa a la construcció a causa de les seues propietats i cost final. Inicialment, les fibres de polipropilè eren usades únicament en el formigó per controlar la fissuració per retracció. No obstant això, en l'última dècada, la industria química ha desenvolupat fibres més grans i amb millors prestacions d'adherència, que permeten a aquestes fibres complir amb requisits per a ser utilitzades estructuralment. En aquest context, la present tesi pretén ser una contribució al coneixement sobre el formigó reforçat amb fibres (Fibre-reinforced concrete - FRC), especialment en l'efectivitat de les fibres de polipropilè com a reforç a tallant. Per això, primer es realitza un estudi bibliogràfic del formigó reforçat amb fibres de polipropilè (PFRC) com a material i les seues plicacions estructurals. Aquest estudi també tractarà sobre els paràmetres que afecten el comportament a tallant del formigó tradicional i del formigó reforçat amb fibres. Per avaluar l'efectivitat de les fibres de polipropilè en el tallant, es realitzaran tres campanyes experimentals. Cada campanya representa un nivell d'estudi diferent. El primer és a nivell material on s'avalua el comportament a tallant a través d'espècimens tipus Push-off. El segon nivell, correspon a l'estudi del tallant en elements a escala real. Per això es fabriquen i assagen bigues esveltes crítiques a tallant. L'últim nivell correspon a una aplicació real de fibres de polipropilè actuant com a reforç a tallant. En aquesta campanya, es fabriquen i assagen plaques alveolars de gran cantell amb seccions i condicions de suports reals.
Ortiz Navas, FR. (2020). Effectiveness of polypropylene fibres as shear reinforcement in structural elements [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/153147
TESIS

Tese de doutoramento em Engenharia Civil
In a recent experimental program dealing with the Near Surface Mounted (NSM) technique for the flexural strengthening of continuous reinforced concrete (RC) slabs strips, the increase of load carrying and the moment redistribution was lower than the expected values. This experimental program was analysed in depth in this thesis and it was concluded that more efficient flexural strengthening arrangements can be applied if carbon fibre reinforced polymer (CFRP) laminates (of rectangular cross section) are applied not only in the intermediate support (hogging region), but also in the positive bending moment zones (sagging regions). Thus, an experimental and a numerical research program were carried out, and it was verified the possibility of increasing the load carrying capacity in 25% and 50%, maintaining a relatively high level of moment redistribution, when correct NSM flexural strengthening arrangements are used. For assessing the predictive performance of a FEM-based computer program, the experimental tests were simulated by considering the nonlinear relevant aspects of the intervening materials. After has been concluded about the capability of this model to simulate the behaviour of this type of structures, a parametric study was carried out to investigate the influence of the strengthening arrangement and CFRP percentage in terms of load carrying capacity and moment redistribution capacity of continuous RC slab strips flexurally strengthened by the NSM technique. Additionally, to predict the load-deflection response of this type of structures up to its collapse, an analytical model was developed and its performance was appraised by using the data obtained from the experimental program. This model is based on the flexibility method and requires the knowledge of the flexural stiffness of the representative cross sections of the structure, which can be determined from the moment-curvature relationship of these sections. The increase of the load carrying capacity of the strengthened slabs can, however, can be limited by the formation of a shear failure crack in the hogging region. To avoid the occurrence of this brittle failure mode, a new technique, designated Embedded Trough Section (ETS) was developed, and its effectiveness was appraised by testing two series of RC beams of different cross section. Finally, the most relevant conclusions extracted from the present study are presented, and further research developments are suggested.
Num programa experimental recentemente realizado sobre o reforço à flexão de faixas de laje contínuas de betão armado (BA) reforçadas segundo a técnica NSM (Near Surface Mounted, nomenclatura inglesa), o aumento da capacidade de carga e de redistribuição de momento foi inferior ao esperado. Este programa experimental foi analisado em profundidade nesta tese e foi concluído que existem configurações de reforço à flexão mais eficientes que podem ser utilizadas se laminados de fibra de carbono (CFRP) forem aplicados não só na região de apoio central (momento negativo), mas também na região de momentos positivos. Nesse sentido, um programa experimental e numérico foi levado a cabo, e verificou-se a possibilidade de aumentar a capacidade resistente em 25% e 50%, mantendo um nível de redistribuição de momentos relativamente elevada, quando se usam sistemas de reforço NSM adequados. Para avaliar a capacidade de previsão um software baseado no Método dos Elementos Finitos (MEF), os resultados experimentais foram simulados considerando os aspectos mais relevantes do comportamento não-linear dos materiais intervenientes. Após a conclusão deste estudo sobre a capacidade de simulação do comportamento deste tipo de estruturas com este modelo, foi realizado um estudo paramétrico para investigar a influência da disposição do reforço e da percentagem de CFRP na capacidade de carga e capacidade de redistribuição de momento em faixas de laje contínuas reforçadas segundo a técnica NSM. Além disso, um modelo analítico foi desenvolvido para prever a relação força-flecha deste tipo de estruturas até o seu colapso e o seu desempenho foi avaliado usando os dados obtidos no programa experimental. Este modelo é baseado no método de flexibilidade e pressupõe o conhecimento da rigidez à flexão das secções transversais representativas da estrutura, a qual pode ser determinada a partir da relação momento-curvatura destas secções. O aumento da capacidade de carga pode, no entanto, ser comprometido pela formação de fendas de corte junto aos apoios centrais dos elementos estruturais reforçados. Para evitar a ocorrência deste tipo de rotura frágil, uma nova técnica de reforço, designada por Embedded Trough Section (ETS, na nomenclatura inglesa) foi desenvolvida, e a sua eficácia foi avaliada por meio de ensaios de duas séries de vigas com diferentes seções transversais. Finalmente, as principais conclusões extraídas da investigação desenvolvida ao longo deste trabalho são apresentadas, e desenvolvimentos futuros são sugeridos.

The rational use of natural, economic and social resources in order to ensure the sustainability and a long-term balance has become one of the largest global concerns. In the civil engineering field, the limited durability of steel reinforced concrete structures, especially in aggressive environments, and the high costs of the repair and maintenance operations have motivated the search for alternative materials and solutions to steel. One of these alternative reinforcements is the glass fibre reinforced polymer (GFRP) bars due to their immunity to corrosion, which is an important advantage when comparing to steel. However, several factors such as the novelty in the market, the high fabrication costs, the different design philosophies and the uncertainties of its behaviour with the concrete have been delaying the use of the GFRP bars in a larger scale. This thesis aims to contribute to the scientific knowledge of the GFRP reinforced concrete, as it studies its behaviour and design. The research work is mainly experimental and is based on a campaign with 24 full-scale reinforced concrete (RC) beams 4.30 m long and rectangular crosssection of 0.25 x 0.40 m2, divided into two groups with different purposes: - 18 beams to study the performance of different GFRP bar layouts as shear reinforcement; - 6 beams to assess the behaviour of a rehabilitation solution with GFRP bars to replace the deteriorated flexural steel reinforcement. The specimens of the first group were designed to fail due to shear with four different GFRP shear reinforcement solutions: 1) closed hoop GFRP stirrups, 2) two C shaped GFRP bars forming a stirrup, 3) two double headed GFRP bars and 4) two simple straight GFRP bars. Two shear reinforcement ratios with different spacing were also tested with the closed hoop GFRP stirrups. For each GFRP shear reinforcement layout, three different longitudinal stiffnesses were considered using steel and GFRP bars with different ratios. The beam specimens were tested until failure under a four point loading set-up and both the serviceability and the ultimate performance were analysed. The results were reported in terms of deflections, crack pattern, crack width, strains in the longitudinal and shear reinforcements, ultimate load capacity and failure modes. The different shear layouts were compared regarding their load carrying performance and their field implementation easiness. The design of the beams and their result predictions were made according to the existing guidelines and codes. It was concluded that the closed hoop stirrups and the C-stirrups were the most efficient and that the beams load capacity was highly underestimated by the GFRP codes. To improve the design formulas of these codes, different values for the limit strains and for the strut angle were proposed. The double headed bars as shear reinforcement were also efficient in the cases with higher longitudinal stiffness because it contributed to keep the integrity of the beam by exhibiting low deflections and crack widths. It was observed that a wide crack at the end of these bars highly compromises the anchorage function of the head. The solution of the simple straight bars was not effective because of the lack of anchorage length. The idea for the second group of beams was inspired on the RC structures with deteriorated bottom concrete due to the corrosion of the longitudinal steel reinforcement. Actually, no steel corrosion was considered in these specimens, but they were concreted in two phases to simulate the replacement of the deteriorated concrete, starting at the stage after its complete removal. The rehabilitation procedure consisted on the insertion of the longitudinal GFRP bars and the concreting of a new bottom layer in the beam. Two solutions with different GFRP longitudinal cross-section areas were designed according to the existing guidelines, one to restore the ultimate load capacity of the original beam, and the other to maintain the deflection of the original beam. The ends of the GFRP bars were conic heads to compensate their lower anchorage length. The rehabilitated beam specimens were subjected to 3 point bending tests until failure, and their service and ultimate behaviour were analysed. Results are presented in terms of deflection, crack pattern, mid-span crack width, reinforcement strains, ultimate flexural capacity and failure modes. It was concluded that this technique was effective for both the serviceability and ultimate limit states of the rehabilitated beam, as it was able to restore the deflection and the load capacity of the original beam, and that the existing GFRP design documents can be used. Although this was mainly an experimental research work, a simple but reliable two-dimensional finite element (FE) model was defined using ATENA software to simulate the tests, which helped to better understand some issues regarding the specimens behaviour and enabled to extrapolate some results of non-tested possibilities. The linear and nonlinear behaviour of all materials was adequately modelled by appropriate constitutive laws. Furthermore, numerical results were compared with the experimental results. Results show that, in general there was a good agreement between the overall modelling results and the experimental ones. The constructed models were able to predict the experimental behaviour in terms of ultimate capacity and load-deflection curves. Regarding the first group of beams, two additional stirrups spacing were modelled in order to clarify its influence in the shear capacity. It was simulated different longitudinal reinforcement ratios to assess its influence in the shear capacity. As a final remark, the results of the present work show that the use of GFRP bars is viable in RC structures, which contributes to more durable structures in long-term. This material can be used as longitudinal and shear reinforcement of new structures and as a rehabilitation solution to replace the corroded steel in deteriorated structures.