Academic literature on the topic 'Diagonal cracking'

The shear failure of reinforced concrete beams is one of the fundamental problems in civil engineering; however, the diagonal tension strength of reinforced concrete (RC) beams without stirrups is still in question. This paper focuses on the prediction of diagonal cracking strength of RC slender beams without stirrups. In slender beams, flexural cracks develop in the tension zone prior to a diagonal cracking. Using the basic principles of mechanics, but cracking included, and theory of elasticity, a diagonal cracking strength equation is proposed for both normal and high strength concrete beams. The proposed equation, the requirements of six codes of practice and seven equations proposed by different researchers are compared to the experimental results of 282 beams available in the literature. It is found that the predictions from the proposed equation are in good agreement with the experimental results. Santrauka Gelžbetoninių sijų suirimas įstrižajame pjūvyje – viena pagrindinių problemų statybos inžinerijoje. Tačiau skersine armatūra nearmuotų gelžbetoninių sijų įstrižasis tempiamasis stipris nėra visiškai ištirtas. Šiame straipsnyje nagrinėjamas siaurų, be skersinės armatūros gelžbetoninių sijų įstrižojo pjūvio pleišėjimas. Siaurose sijose plyšiai tempiamojoje zonoje atsiranda anksčiau negu įstrižajame pjūvyje. Taikant klasikinius mechanikos principus ir tamprumo teoriją, pasiūlyta normalaus stiprio arba stipriojo betono sijų istrižojo pjūvio atsparumo pleišėjimui apskaičiavimo lygtis. Siūloma lygtis, pagrįsta šešių projektavimo normų reikalavimais ir septyniomis kitų autorių lygtimis bei palyginta su literatūroje pateiktais 282 sijų eksperimentinių tyrimų rezultatais. Nustatyta, kad pagal siūlomą lygtį atlikti skaičiavimai gerai sutampa su eksperimentiniais rezultatais.

In order to study the shear resistance and design method of hybrid fiber (steel fiber and polypropylene fiber) reinforced high performance concrete deep beams, the shear tests were conducted according to the orthogonal experimental design. The contributory factors such as the characteristic parameters of steel fiber (types, volume fraction, aspect ratio), the volume fraction of polypropylene fiber, the ratio of web horizontal reinforcement and the ratio of web vertical reinforcement were analyzed. Results illuminate that shear failure mode of hybrid fiber reinforced HPC deep beams are splitting failure and diagonal compression failure. Hybrid fiber can notably increase the diagonal cracking strength and shear strength of HPC deep beams. The diagonal cracking strength is increased by 5.6%~83.8% while the shear strength is increased by15.6%~35.2%. A formula to calculate the shear resistance of hybrid fiber reinforced HPC deep beams is put forward based on spatial strut-and-tie mode and splitting failure. Meantime test verification is carried out and the calculated results are satisfied.

Brazilian Codes NBR 6118 and NBR 15575 provide practical values for interstory drift limits applied to conventional modeling in order to prevent negative effects in masonry infill walls caused by excessive lateral deformability, however these codes do not account for infill walls in the structural model. The inclusion of infill walls in the proposed model allows for a quantitative evaluation of structural stresses in these walls and an assessment of cracking in these elements (sliding shear diagonal tension and diagonal compression cracking). This paper presents the results of simulations of single-story one-bay infilled R/C frames. The main objective is to show how to check the serviceability limit states under lateral loads when the infill walls are included in the modeling. The results of numerical simulations allowed for an evaluation of stresses and the probable cracking pattern in infill walls. The results also allowed an identification of some advantages and limitations of the NBR 6118 practical procedure based on interstory drift limits.

This paper addresses the effects of hooked-end steel fibre contents on the mechanical properties of high-performance concrete (HPC) and investigates the feasibility of utilizing steel fibres to simplify the complicated reinforcement detailing of critical HPC members under high shear stress. Mechanical properties of HPCs with specified compressive strength of 60 and 100 MPa include the flow, air content, compressive strength, and flexural strength. The effectiveness of 1.50% steel fibre content on the shear behaviour of diagonally reinforced concrete coupling beam without additional transverse reinforcement was investigated to alleviate complex reinforcing details for the full section confinement of diagonal bar groups. The test results revealed the incorporation of steel fibres significantly affected the mechanical properties of the HPCs. For diagonally reinforced coupling beam (SFRCCB) without additional transverse reinforcement, the addition of 1.5% steel fibre content into 60 MPa HPC coupling beam provides similar cracking and structural behaviours compared to those of diagonally reinforced coupling beam (CCB) with full section confinement details. However, the ductility of SFRCCB was less than that of CCB. It is recommended that both stirrups and steel fibre should be used for fully confining the diagonal bar groups of coupling beams to achieve the ductile behaviour.

The wall pier represents the vertical element of multi-storey walls with openings, the main resistant structural components of a masonry building. Structural systems of wall piers and spandrels are required to sustain the in-plane seismic actions acting on the wall, opposing with their weights to the action of horizontal forces. The behavior of masonry constructions results to be very far from the one characterizing ductile structures, because of the lack of energy dissipation during the deformation. A strength resource of masonry structures, properly reinforced in order to avoid early local failures, consists in exhibiting rocking behavior, until a failure condition is attained. An investigation on the dynamic behavior of masonry wall piers is carried out by following Housner’s studies and properly introducing the effect of diagonal cracks, shown by typical post-earthquake cracking patterns. As a consequence, the system is characterized by the detachment of a lower triangular region that becomes ineffective during the development of the mechanism and does not oppose with its weight to the overturning. Finally, it is shown that the occurrence of diagonal cracks can be prevented by the execution of suitable retrofit interventions.

In order to investigate the effect of steel fiber and polypropylene fiber on shear behavior of HPC deep beams, the shear tests were conducted on 18 different groups of deep beams with steel fiber and polypropylene fiber and 2 groups of HPC deep beams without fiber according to the orthogonal experiment. 6 factors, including the shape of steel fiber, the volume fraction of steel fiber, the aspect ratio of steel fiber, the volume fraction of polypropylene fiber, the ratio of web horizontal reinforcement and the ratio of web vertical reinforcement, were compared by direct-viewing analysis. Results illuminate that hybrid fibers greatly increase the diagonal cracking strength and shear strength of HPC deep beams. The aspect ratio of steel fiber plays the most important role in diagonal cracking strength whereas the ratio of web vertical reinforcement has minimum effect. Meanwhile the ratio of web horizontal reinforcement plays the most important role in shear strength whereas the volume fraction of polypropylene fiber has minimum effect. An anti-cracking capacity for inclined section calculation formula and a shear bearing capacity calculation formula for hybrid fiber reinforced HPC deep beams are put forward based on current code. Meantime test verification is carried out and the calculated results are satisfied.

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This study presents the results of an experimental research on shear in self compacting concrete beams. The influence of beam depth and longitudinal reinforcement ratio in beams was evaluated and results compared with similar beams cast with conventional concrete beams. Cracking, deformations in compression strut, vertical displacements, reinforcement deformation and load failure and failure mode were evaluated. Sixteen 1000 mm long beams with a 150 mm cross sectional width were tested. Eight beams were cast with self compacting concrete and eight with conventional concrete. Both were designed for a concrete fck = 25 MPa. The longitudinal reinforcement of each beam was design to ensure shear failure. Each group consisted of eight beams with four beams had a longitudinal reinforcement ratio of 1.3% and beam depths of 20 cm, 25 cm, 30 cm and 35 cm in height, and the other four beams had longitudinal reinforcement ratio of 2,3% with the same beam depths. The beams were instrumented with seven LVDT's, five of which were positioned to read vertical displacements and the other two were glued on the side of the beam for measuring crack width and displacements in the compression strut. Four strain gages used in the beam’s longitudinal and transverse reinforcement. The beams were tested to failure with a concentrated load at midspan. The results showed that all the beams failed by crushing of the concrete compression zone above the shear crack. Overall, conventional concrete beams ultimate loads were between 9% and 18% greater than those obtained with the self compacting concrete beams, and the difference was slightly higher in the beams with 1.3% of longitudinal reinforcement ratio. This increased resistance of conventional concrete beams was due to greater aggregate interlock which occurs due to the greater number and larger maximum aggregate size in conventional concrete. Interlock mechanism was also responsible for the largest width of diagonal cracks in conventional concrete beams, on average 21% higher than in self compacting concrete beams, and the ratio between higher ultimate load and load at the first diagonal crack, on average 28% higher. The largest diagonal crack width led the transverse reinforcement of the conventional concrete beams to deform, on average, 64% more than the self compacting concrete beams. All three standards considered (NBR 6118:2007, Eurocode and ACI 318:2011 2:2003) were conservative and underestimated the ultimate shear load, mainly by the fact that in none of them take into account the arching action, which occurs in beams with ratio a/d < 2.5. The average ultimate loads of the beams were 73.1% higher than those calculated by the standards.
Este estudo apresenta os resultados de uma pesquisa experimental sobre cisalhamento em vigas de concreto auto adensável. Foi avaliada a influência da altura da viga e da taxa de armadura longitudinal em vigas e feita uma comparação de resultados com vigas de concreto convencional abordando fissuração, deslocamentos na biela de compressão, deslocamentos verticais, deformação nas armaduras e carga e modo de ruptura. Foram ensaiadas dezesseis vigas com 1000 mm de comprimento e 150 mm de base, sendo que oito vigas foram de concreto auto adensável e oito de concreto convencional. Ambos os concretos foram projetados para um fck = 25 MPa. A armadura longitudinal de cada uma das vigas foi dimensionada pra garantir que houvesse ruptura por cisalhamento. Cada grupo de oito vigas era composto por quatro vigas com taxa de armadura longitudinal de 1,3%, que tinham alturas de 20 cm, 25 cm, 30 cm e 35 cm, e quatro vigas com taxa de armadura longitudinal de 2,3%, com as mesmas alturas. As vigas foram instrumentadas com sete LVDT’s, sendo que cinco foram posicionados para leitura de deslocamentos verticais e os outros dois foram colados na face lateral da viga para medição da largura de fissuras e de deslocamentos na biela de compressão, e quatro extensômetros elétricos, sendo que dois foram colados na armadura transversal e os outros dois na armadura longitudinal. As vigas foram ensaiadas de uma só vez até a ruptura com uma carga concentrada no meio do vão entre apoios. Os resultados mostraram que todas as vigas romperam por esmagamento do bordo comprimido acima da fissura de cisalhamento. Em geral, as vigas de concreto convencional tiveram cargas de ruptura entre 9% e 18% maiores que as vigas de concreto auto adensável, sendo que a diferença foi ligeiramente maior nas vigas que tinham 1,3% de taxa de armadura longitudinal. Esta maior resistência das vigas de concreto convencional foi atribuída ao maior mecanismo de intertravamento entre agregados graúdos destas vigas, que ocorre devido ao maior número e maior dimensão máxima característica dos agregados. O mecanismo de intertravamento entre agregados também foi o responsável pela maior largura de fissuras diagonais nas vigas de concreto convencional, em média 21% maior que nas vigas de concreto auto adensável, e pela maior relação entre carga de ruptura e carga de surgimento da primeira fissura diagonal, sendo em média 28% maior. A maior largura de fissuras diagonais fez com que a armadura transversal das vigas de concreto convencional deformasse em média 64% mais do que as vigas de concreto auto adensável. Todas as três normas consideradas (NBR 6118:2007, ACI 318:2011 e EUROCODE 2:2003) foram conservadoras e subestimaram a carga de ruptura devido ao esforço cortante, principalmente pelo fato de que em nenhuma delas é levada em consideração a ação de arco, que ocorre em vigas com relação a/d < 2,5. Em média, as cargas de ruptura das vigas foram 73,1% maior que as calculadas pelas normas.

Concrete deep beams with a shear span to depth ratio of less than 2.32 [73] will work as tied arches after flexural cracking, provided there is sufficient reinforcement. The compression strut formed between the support and the loading points is under biaxial compressive and tensile stresses. The current Canadian Code [5] stipulates that deep beams and corbels should be designed using the Strut-and-Tie Method. This method incorporates the work done by Collins and Mitchell [8][9] where the cracked concrete behaves as a new material and that the compressive strength of concrete is reduced due to strain-softening. Here-in lies an area of discrepancy. The work done by Collins and Mitchell utilizes beam theory which requires that plane sections remain plane. However, deep beams and corbels are classified as "regions of discontinuity" consequently beam theory does not apply to these structures. An area of the Canadian code which needs to be examined is the dimensioning of the compression strut. To date there is no clear explanation as to how the design guidelines of the compression strut were developed. A weakness of the design code is that numerous assumptions must be made. The designer first assumes that the compression strut reaches a maximum concrete strain of 0.002 [5] , and then must assume the strains in the tension ties. The focus of this research has been to investigate diagonal splitting strength of reinforced concrete deep beams. In conducting this study, twelve deep beams, categorized in four groups were tested. The test variables included the shear span, the amount of web reinforcement and the concrete compressive strength. Surprisingly, no researcher has published measured strain incurred by the compression strut in deep beams. In our research, a single beam from each of the four test groups was fitted with strain gauges to measure the tensile strain in the main tensile reinforcement. As well, the concrete strains along the main diagonal formed between the support and the loading points as well as perpendicular to the strut were measured. The experimental work demonstrated the development of diagonal cracking. These cracks appeared above the supports and propagated towards the loading points. The strain gauges on the concrete surface confirmed that the stresses along the compression strut were under biaxial compression tension stresses. A finite element analysis determined that the compression stress acting parallel to the diagonal were uniform in distribution and symmetrical. Perpendicular to the diagonal, high compressive stresses were seen at the supports and the loading points. However, the stresses in between these areas were uniformly distributed in tension. The measured compressive strains were much less than the recommended value of 0.002, and the compression strut was found to be much wider than that defined by the Canadian Code. As a consequence of these the findings, a truss model was defined using a biaxial concrete strength envelope. This truss model was applied to the test beams of this study as well as too ninety-nine test beams available in literature. In all cases, the truss model was able to accurately predict the strength of these test beams.

<p>Two test series with various UHPC strengthening interventions were conducted in this study to investigate the behaviour of composite reinforced concrete (RC) slabs strengthened with UHPC. The first, RE series is a retrofit interventions, tested UHPC as patch material for repairing deteriorated concrete structures. As for the second, OV series is a UHPC overlay interventions, was used to strengthen soffit of RC slab members. The results showed that, in RE series, UHPC safeguard against diagonal cracking compare to conventional RC slab. The UHPC exhibited excellent energy absorption with extensive deflection hardening and ductility during the post cracking range. In OV series, all slabs showed formation of diagonal shear cracks and sign of debonding modes. The UHPC overlay delayed the development of shear cracking. The ultimate load carrying capacity and tendency of flexural failure increase with the overlay thickness.</p>

<p>Recently, composite girder cable-stayed bridge is widely used in the world. Since the existing design method takes less focus on the principal stress of the top and bottom slab, the cracking problem of the concrete bridge deck has not been solved perfectly yet. Based on the spatial grid model, this paper takes Guan He Bridge in Jiangsu province as an example to analyze this kind of structure. Monitoring the principal stress of the concrete bridge deck is proposed for the first time to study the effect of diagonal crack. The principal stress of the concrete deck in the middle span, the quartile span, one-eighth of the span, the side span, the bridge tower, and the auxiliary pier are observed respectively. Comparing the theoretical values with the measured value, the results show that the actual stress state of the whole concrete bridge deck during construction is in accordance with the theoretical calculation. For composite girder cable-stayed bridge, the concrete bridge deck is prone to crack, so it is very significant to control the quality in the construction stage, which can provide a guarantee for the safety and durability of the structure.</p>

Following the warning of a flooded bow horizontal brace of a semi-submersible production platform, an inspection diving team was mobilized and cracks were found at both bow and aft K-joints. Analysis of the service life of the platform, together with the results of structural analysis and local strain measurements, concluded that cracking was caused by fatigue initiated at high stress concentration points on the gusset plates inserted in the tubular joints. As a consequence of the fractured plates other cracks were nucleated close to the intersection lines of the braces that compose the K-joints. Based on this analysis different repair possibilities were proposed. To comply with the production goals of the Business Unit it was decided to repair the platform on-site and in production in agreement with the Classification Society. The proposed repair contemplated the installation of two flanges on the gusset plates between the diagonal braces by underwater wet (UWW) welding. Cracks at the gusset plates were also removed by grinding and wet welding. Defects located at the braces are being monitored and repaired by the installation of backing bars, by wet welding, followed by grinding and welding from the inside. To carry out the job two weld procedures and ten welder-divers were qualified.

Structural materials of next generation nuclear reactors are expected to experience severe operating conditions including intense heat, high irradiation doses, thermal and mechanical stresses, and corrosive environments, which would potentially degrade material properties and impose severe threat to structural integrity. For example, high irradiation doses cause the evolution of displacement cascades, consisting of point defects, which lead to void swelling, irradiation creep, irradiation assisted stress corrosion cracking, and embrittlement. Over the last several decades, extensive computational researches have been conducted to study displacement cascades and generate defect statistics over a wide range of irradiation doses and temperatures for pure materials, primarily Fe. However, very limited data can be found to determine cascade evolution and defect statistics of Fe-alloys under pressure. In this work, large-scale molecular dynamics simulations have been performed to study displacement cascade and generate defect statistics of Fe-10%Cr alloy under uniaxial pressure. The selection of the material is based on the fact that Fe and Cr are the two major alloying elements of Ferritic-martensitic steels, which have shown promise to be a candidate material for future generation reactors due to high temperature stability and reduced swelling under irradiation. The simulated material is built from a single crystal Fe model of [130], [310], and [001] orientation, and randomly substituting Fe atoms by Cr. Empirical EAM potential has been used to define interatomic interactions. Irradiation simulations are performed for doses between 2–15keV, and pressure ranges between −10,000 bars to +10,000 bars applied along the x-direction. Simulation temperature is kept at a minimum, e.g. 15K, to minimize thermal influences. Displacement cascades are generated by imparting kinetic energy to a lattice atom (i.e. primary-knock-on-atom, PKA) along an arbitrary crystallographic direction (i.e. the diagonal direction of the simulation cell). Point defects are identified using the Wigner-Seitz method. Upon collision, the PKA atom displaces the surrounding atoms from their perfect lattice cites and causes a rapid increase in defect numbers. As the imposed energy is dissipated through the crystal, the displaced atoms recombine with the vacancies and the defect numbers gradually decrease and become stable. The cascade structure shows the presence of the vacancies at the core of the cascades surrounded by the interstitials. The number of defects increases almost linearly with increasing the irradiation dose for any pressure. The effect of pressure is found to be more profound within the intermediate pressure range, e.g. between −100 to +1000 bar, within which the number of point defects continually decreases as the pressure changes from tension to compression. The trend is found to be consistent for the whole PKA energy range. Point defects are also found to form defect clusters. The common neighbor analyses haves been performed to determine the structure of the clustered defects. It has been revealed that the defect clusters are of cubic diamond type. Additional analyses are currently under progress to evaluate the influence of pressure on cascade volume, point defect composition, and cluster composition.