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In this study, full-scale loading tests were conducted to investigate web-shear strengths of hollow-core slab (HCS) members strengthened in shear by using practically viable methods. All the HCS units used in the current test program were fabricated by using the individual mold method, not by the extrusion method, and the key experimental variables of the shear test were set as the presence of shear reinforcement, core-filling concrete, topping concrete, and also the magnitude of effective prestress. The shear force-displacement behaviors, crack patterns, and strain response of shear reinforcements were reported in detail. In addition, to identify the shear strength enhancement provided under various strengthening conditions in a quantitative manner, existing shear test results of series specimens, including a naked HCS member and corresponding composite HCS members with cast-in-place (CIP) concrete and/ or shear reinforcements, were collected from literature. On this basis, a practical design expression capable of estimating shear strengths of HCSs strengthened with CIP concrete and stirrups was suggested based on the ACI 318 code equation. The proposed method evaluated the shear strengths of the collected specimens with a good level of accuracy, regardless of the presence of core-filling concrete, topping concrete, and shear reinforcements. [ABSTRACT FROM AUTHOR]

For the past several decades, there has been an ongoing academic challenge to understand the shear-transfer mechanism in reinforced concrete (RC) members, particularly in those with small shear span-depth ratios, also known as deep beams. Analytical uncertainty regarding shear strength inevitably increases when those deep members are strengthened in shear using externally bonded fiber-reinforced polymer (FRP) composites. This study aims to investigate the complex, interrelated effects of short shear span-depth ratios and FRP composites on RC deep beam members. To this end, the fundamental formulations of the dual potential capacity model (DPCM) are extended to RC deep members reinforced with externally bonded FRP composites. The proposed model can consider the various types of FRP composites, fiber bonding configurations, and fiber layouts, and various failure modes of concrete and FRP reinforcements are also reflected. A total of 131 shear test results of RC deep and short members with externally bonded FRP composites are carefully collected, and those are added to the existing database of RC slender members strengthened with FRP composites. On this basis, the proposed approach is verified by comparing test results with analysis results, and a reasonable level of analytical accuracy is achieved. The statistical data distribution of strength ratios between the test and analytical results is consistent across a range of shear span-depth ratios from approximately 0.7 to 4.0. Overall, the proposed DPCM approach provides a useful tool for analyzing the shear strength of RC deep beam members strengthened with externally bonded FRP composites. [ABSTRACT FROM AUTHOR]

The results of an experimental program conducted to evaluate the performance of shear-critical post-tensioned I-girders with grouted and ungrouted ducts are presented. The experimental program involved the design, construction, and testing to failure of six fullscale specimens with different duct layouts (straight, parabolic, or hybrid) and using both grouted or ungrouted ducts. All tests resulted in similar failure modes, such as localized web crushing in the vicinity of the duct, regardless of the duct condition or layout. Furthermore, the normalized shear stresses at ultimate were similar for the grouted and ungrouted specimens. The current shear design provisions in the AASHTO LRFD Bridge Design Specifications (AASHTO LRFD) were reviewed, and updated shear-strength reduction factors to account for the presence of the duct in the web and its condition (that is, grouted or ungrouted) were proposed. The data generated from these tests served as the foundation for updated shear-strength reduction factors proposed for implementation in AASHTO LRFD. [ABSTRACT FROM AUTHOR]

This paper presents mechanics-based modeling approaches to understand the shear behavior of squat walls reinforced with glass fiber-reinforced polymer (GFRP) bars when subjected to lateral loading. The applicability of design provisions in published specifications is examined using collated laboratory test data, resulting in the need for developing revised guidelines. Analytical studies are undertaken to evaluate the effects of reinforcement type on the response of load-bearing walls and to establish failure criteria as a function of various stress states in constituents. Obvious distinctions are noticed in the behavior of squat walls with steel and GFRP reinforcing bars owing to their different reinforcing schemes, tension-stiffening mechanisms, and material properties. Newly proposed equations outperform existing ones in terms of predicting the shear capacity of GFRP-reinforced squat walls. Furthermore, based on geometric and reinforcing attributes, a novel determinant index is derived for the classification of structural walls into squat and slender categories, which overcomes the limitations of prevalent methodologies based solely on aspect ratio. A practical method is suggested to adjust the failure mode of walls with GFRP reinforcing bars, incorporating a characteristic reinforcement ratio. [ABSTRACT FROM AUTHOR]

The use of normal-strength (Grade 60) and high-strength (Grade 80) headed bars as transverse reinforcement can improve the constructability of reinforced concrete structures. However, the ACI 318-19 Code does not allow the use of headed bars as transverse reinforcement in deep beams. ACI 318-19 also does not allow engineers to take advantage of the increased yield strength of Grade 80 reinforcement for use as shear reinforcement. This paper presents an analytical evaluation of shear-critical deep beams that use high-strength headed reinforcement. Six recently conducted largescale experiments are modeled using the two-parameter kinematic theory, the nonlinear finite element tool VecTor2, and strut-and-tie methods described in codes. The predictions are compared with experimental results. A parametric study is conducted to evaluate the influence of the quantity of transverse reinforcement and yield stress of the transverse reinforcement on the response of shearcritical deep beams. [ABSTRACT FROM AUTHOR]

Using normal-strength (Grade 60) and high-strength (Grade 80) headed bars as shear reinforcement can improve the constructability of reinforced concrete structures. However, the ACI 318-19 Code does not allow the use of headed bars as transverse reinforcement in deep beams. Similarly, ACI 318-19 does not allow engineers to take advantage of the increased yield strength of Grade 80 reinforcement for use as shear reinforcement. Therefore, to investigate the performance of headed and high-strength transverse reinforcement on the shear behavior of deep beams, a series of six large-scale specimens were tested to failure. The member response, including crack widths and strains in transverse reinforcement, were examined. The results show that deep beams containing headed and high-strength transverse reinforcement performed well compared to companion tests using conventional reinforcement. [ABSTRACT FROM AUTHOR]

This paper discusses the behavior of large-scale reinforced concrete deep beams that failed in shear and were monitored with full field-of-view, digital image correlation (DIC) equipment. Six shear-critical deep beams, measuring 4.88 x 1.11 m, were tested to failure. The specimens were point-loaded and simply supported, with three members examining the influence of asymmetrical loading conditions. The members were tested with various loading plate sizes and shear span-depth ratios. High-resolution displacement and strain field data obtained throughout loading are used to examine the member response. Principal compressive strain field diagrams of the deep beams at peak load are discussed. The paper presents crack patterns and crack kinematics, including crack widths and crack slips along critical shear cracks, determined from the DIC data throughout loading. The paper discusses crack dilatancy--that is, crack slips versus crack widths--along critical shear cracks, throughout loading, and at multiple locations. The results improve understanding of the detailed displacement field response of large shear-critical reinforced concrete deep beams, which can be used to improve kinematic and constitutive models, such as aggregate interlock models, for large-scale members. [ABSTRACT FROM AUTHOR]

This paper investigates the response of reinforced concrete shell elements subjected to all eight stress resultants (in-plane shear, two out-of-plane shears, torsion, two axial loads, and two moments). Twelve new experiments subjected to different combinations of in-plane and out-of-plane loads are presented. The experiments examine the influence of varying quantities of transverse shear reinforcement and concrete strengths. The paper also presents a new nonlinear, high-powered, macro finite element model called Shell II. The Shell II method is a three-layered model based on the equations of the Modified Compression Field Theory and is capable of predicting the full three-dimensional load-deformation response of shell elements subjected to combined loads. Shell II is also used to examine the experimental results in the context of in-plane versus out-of-plane shear-stress interaction diagrams. The results highlight the importance of considering combined loading in predicting the response of shells in three dimensions. [ABSTRACT FROM AUTHOR]

Reinforced concrete beams are typically reinforced transversely with rectilinear stirrups made from steel reinforcing bars to resist shear. The process of making stirrups requires extended time and considerable labor, and results in relatively large tolerances. This study aims at studying the viability of using welded wire reinforcement (WWR), cold-formed into the shape of a closed steel cage to resist the shear load effect. To accomplish the objective of the study, 16 half-scale beams were tested by a universal testing machine under displacement-controlled loading conditions. The study considered different wire diameters (4, 6, and 8 mm [0.16, 0.24, and 0.32 in.]), grid openings (25, 50, and 100 mm [1, 2, and 4 in.]), shear span-to-thickness ratios (2.5 and 3.0), and transverse steel reinforcement ratios (251 and 505 N/mm [1433 and 2884 lb/in.]). A comparison was carried out between the test results of WWRreinforced beams and corresponding stirrup-reinforced beams in terms of the crack formation characteristics, stiffness, shear strength, residual strength, and ductility. Findings of the study showed that the WWR-reinforced beams possessed 2 to 17% higher shear strength than the corresponding stirrup-reinforced beams, without a compromise in the ductility. The predicted shear strength based on ACI 318 was within 10% of the strength obtained by the experiments. [ABSTRACT FROM AUTHOR]

This paper presents the behavior of glass fiber-reinforced polymer (GFRP)-reinforced ultra-high-performance concrete (UHPC) beams without shear stirrups. An experimental program is conducted to examine the implications of variable geometric, loading, and reinforcement configurations, particularly for the effective depth-to-height ratio (0.75 ≤ d/h ≤ 0.90), shear spandepth ratio (1.18 ≤ a/d ≤ 3.23), and GFRP reinforcement ratio (1.35% ≤ ρf ≤ 4.85%) of the beams. Also tested are UHPC cylinders and prisms under axial compression and three-point bending. The strength development of UHPC is remarkable during the first 3 days of casting, after which a gradual and asymptotic growth rate is associated because of saturated pores and the limited attractions of calcium-silicate-hydrate networks. Compared with the factors related to the placement of the GFRP reinforcing bars (d/h and ρf), the a/d is more influential in controlling the capacity and the postpeak deformation of the beams by altering load-transfer mechanisms. The stress of a shear-compression zone is redistributed under arch action and results in supplementary cracks along the beam span. The horizontal splitting of UHPC at the reinforcing bar level caused by the dowel action of GFRP is dependent upon the reinforcement ratio. Analytical models are formulated, and design guidelines are recommended. [ABSTRACT FROM AUTHOR]

Coupling action developed by interfacial shear along vertical connections between precast concrete (PC) wall segments has significant impacts on the seismic performance of a precast shear wall building system. This study investigated the effect of various seismic details on lateral performances of coupled intermediate precast shear wall systems through reversed cyclic tests, and direct shear tests were also conducted to characterize local interfacial shear behaviors between individual PC wall segments. On this basis, a series of numerical investigations were then carried out to further identify how the interfacial shear behavior affects the seismic responses of PC shear wall systems through an advanced finite element (FE) analysis approach. To this end, several interfacial shear curves were generated considering various combinations of the maximum shear capacities, stiffness, and post peak responses, and subsequent nonlinear cyclic analyses were conducted. It was numerically confirmed that the maximum interfacial shear strength is a key influential factor to the lateral flexural strength of PC shear wall systems, while stiffness and post-peak strength degradation of interfacial shear curves affect their energy dissipation and lateral drift capabilities, respectively. [ABSTRACT FROM AUTHOR]

The shear-carrying mechanism in reinforced concrete (RC) has long been uncertain, partly because previously available sensors were insufficient for capturing local behavior. In this study, three large RC beams with stirrups were instrumented with distributed fiber-optic sensors (DFOS) to measure the strain along the full length of the reinforcing bars, while digital image correlation (DIC) was used to measure distributed crack movement to calculate the forces that they transfer. The DFOS measurements along the stirrups showed that the total stirrup force along a shear crack was insufficient to resist the total applied shear. Free-body diagrams (FBD) were constructed along diagonal cracks using the sensor measurements and constitutive relations to investigate if the resulting summation of forces would be in equilibrium, and the results suggest that the main elements of shear resistance have been, at least approximately, identified for the first time with the aid of distributed sensing. [ABSTRACT FROM AUTHOR]

The torsional strength of reinforced concrete members that fail by yielding of the reinforcement can be accurately predicted by design codes such as ACI 318-19 and the Canadian design standard CSA A23.3:19. However, these codes are relatively poor at predicting the strength of heavily reinforced members that fail by crushing. This paper presents a rational model which can predict the strength of such members. A key feature of the model is that the variation in torsional stresses through the thickness of a member is explicitly considered using stress block factors derived from the stressstrain curve of the concrete. The model predicts the strength of 31 experiments with an average test-to-predicted ratio of 1.20 and a coefficient of variation (COV) of 14.4%. This is significantly better than the maximum torsion limits in ACI 318-19 (mean 1.62, COV 21.0%) and CSA A23.3:19 (mean 0.79, COV 41.1%). Simple equations suitable for design are presented. [ABSTRACT FROM AUTHOR]

The safety of existing slab-between-girder bridges is subject to discussion in the Netherlands. Current design codes are conservative for shear-critical girders, and nonlinear finite element analysis is considered a more accurate assessment method. This paper investigates if the Dutch guidelines for nonlinear finite element analysis, which were largely based on laboratory experiments, can safely predict the behavior of large-scale shear-critical post-tensioned girders. The simulation results are compared with experimental observations on girders taken from a demolished bridge (the Helperzoom bridge) after serving for more than 50 years. Predicted and experimentally observed material properties are used as inputs for numerical models. For both, safe predictions of inclined cracking and ultimate capacities are obtained. Parameter studies for load positions and prestress levels are also performed to get a deeper insight into the structural behavior of such girders. This work shows that the guidelines can be used for assessment. [ABSTRACT FROM AUTHOR]

An experimental program consisting of four full-scale specimens was conducted to assess the structural behavior of very large reinforced concrete (RC) pile caps supported on steel pipe piles. The tested specimens replicated the geometry, reinforcement details and placement, material properties, as well as support and loading conditions typical of in-service 1980s vintage pile caps. Prior to testing, three-dimensional (3-D) strut-and-tie models were developed to predict the strength of the specimens and expected failure modes. During tests, widespread reinforcement yielding was observed in all specimens. One specimen failed in one-way shear, two specimens failed in two-way shear, and one specimen did not reach failure before reaching the load capacity of the test setup. Based on the experimental results, the strut-and-tie capacity predictions were highly conservative for all specimens and would have required retrofit of the pile caps to carry the expected column axial loads associated with a potential vertical expansion of the building. The high degree of conservatism is attributed to neglecting the beneficial effects of active confinement in the 3-D structure, especially at the pile locations, that underestimates the available bond strength, thereby minimizing the available tension ties. [ABSTRACT FROM AUTHOR]

Deep members supporting wide loading elements, such as bridge piers or transfer girders, are prevalent in practice but underrepresented in the experimental literature. This paper presents six large-scale deep-beam experiments that use both wide and narrow loading plates, 36 and 12 in. (914 and 305 mm), respectively, with shear span-depth ratios ranging from 1.45 to 2.00. The paper examines the response of these members, including crack patterns and measured strain data. The diagonal crack geometry and results from finite element models indicate that for members with wide loading plates, the compressive stresses are concentrated near the edges of wide elements. This difference in response results in higher shear capacities arising from steeper crack angles when compared to members with smaller loading plates. Nonlinear finite element models using VecTor2 provide reasonable predictions of the member response with a mean test-to-predicted ratio of 1.05. [ABSTRACT FROM AUTHOR]

The availability of high-strength reinforcing bars has prompted engineers to use these in the design of reinforced concrete (RC) beams; their high tensile strength helps to reduce the steel consumption for a given set of design constraints. For every gain, however, there is a risk of some loss in one form or another; results from a parametric study presented herein indicate a substantial savings in the form of quantity of steel in RC beams with the use of high-grade reinforcing bars, albeit it happened with the increased midspan deflection, probable crack width, and bond stresses, as well as the need for the higher reinforcing bar anchorage. The steel grade Fe550 is found to be optimal among all other reinforcing bar grades considered in this study. [ABSTRACT FROM AUTHOR]

This paper presents a method to quantify shear-transfer mechanisms from large-scale reinforced concrete deep beam experiments. The framework uses the Two-Parameter Kinematic Theory in conjunction with basic constitutive relationships to backcalculate the shear-carrying mechanisms in deep beams using only detailed experimental data and member properties. The input to the method is the experimentally obtained displacement field data and critical crack information, including crack widths, crack slips, and member properties; the output of the method is the applied load on the member. The framework is applied to five previously conducted large-scale deep-beam experiments and the assessed loads are compared to the measured applied loads. The results indicate that experimental data including detailed crack geometry, crack widths, and slips can be used to assess the applied load on deep beams. The framework provides a foundation upon which direct crack-based assessment methods can be further developed. [ABSTRACT FROM AUTHOR]

The strut-and-tie approach has gained importance in reinforced concrete design practice in the United States in the last two decades. This method has proven suitable for designing shear-critical structural members where beam theory is not applicable. However, the strength reduction factors specified for the ACI 318 strut-and-tie method have not been calibrated based on the structural reliability approach. Therefore, the reliability of members designed according to these provisions is unknown. In this study, the reliability of deep beams designed using the strut-and-tie method according to ACI 318 building code requirements for structural concrete was determined. Statistical parameters employed for loads, material uncertainty, and fabrication uncertainty were based on published literature. The uncertainty in the analytical model was characterized based on available test results. The findings indicate that current design practice using the strut-and-tie method promotes the likelihood of a nonductile failure mode relative to a ductile failure mode. Inconsistencies in reliability with respect to concrete strength are highlighted. The following reliability-based strength reduction factors are suggested: ϕ = 0.65 for struts and nodal zones and ϕ = 0.90 for ties. [ABSTRACT FROM AUTHOR]

Ultra-high-performance fiber-reinforced concrete (UHPFRC) is a material attracting increased use to solve practical engineering problems. Although significant research has been undertaken to develop constitutive models for finite element modeling of steel fiber-reinforced concrete (SFRC), the reliability of these models in characterizing UHPFRC remains unassessed. Specifically, only limited research is available on rational models for describing postcracking tension and shear-related mechanisms in UHPFRC under various loading conditions. To address these modeling deficiencies, this study investigates existing SFRC material models for their suitability in finite element analysis of UHPFRC. Localized behavior at cracks is investigated, leading to improvements in crack-related formulations through the inclusion of effective aggregate size. An embedded steel reinforcement rupture formulation for elements subjected to tension is also implemented to better capture rupture strains in specimens containing conventional reinforcement. Validation studies are provided to demonstrate the effectiveness of the proposed model improvements. [ABSTRACT FROM AUTHOR]

Throughout the life of existing concrete structures, there is often a need to assess the condition of members exhibiting shear cracks. This paper presents a framework for the crack-based assessment of lightly reinforced concrete deep beams that uses the observed crack geometry in conjunction with the two-parameter kinematic theory to provide member and crack-specific assessments of structural response. The results indicate that the method is able to capture the difference in shear response of nominally identical members that exhibit different crack geometries and is capable of predicting the stress distribution along the critical cracks. This novel approach is then used to examine large-scale deep beam experiments in the literature, and it is shown that the method can capture the response of members presenting different crack shapes with an average experimental-to-predicted ratio for the peak shear force of 1.04 and a coefficient of variation of 3.39%. [ABSTRACT FROM AUTHOR]

For the assessment of existing slab-between-girder bridges, the shear capacity and failure mode are under discussion. In particular, preliminary assessment calculations showed that the critical failure mode of the girders is shear-tension. In this paper, four girders taken from a demolished bridge that were tested in the lab are analyzed according to existing codes. The comparison between the experiments and the analysis shows that the Dutch RBK provisions are conservative and the ACI 318-19 provisions result in good predictions of the shear capacity at inclined cracking and at ultimate. These observations are then combined into recommendations for the assessment of prestressed concrete girders in existing slab-between-girder bridges for shear cracking and the ultimate shear capacity. [ABSTRACT FROM AUTHOR]

A new modeling approach for estimating the shear behaviors of reinforced concrete (RC) beams with corroded longitudinal reinforcements is presented. The corrosion effects on the constitutive models of materials subjected to multi-axial stresses are clarified, including the bond mechanism between the reinforcement and surrounding concrete, which is a critical factor. The material models were implemented in a nonlinear finite element analysis (FEA) platform, and an experimental program is introduced to verify the analysis results. It appeared that the shear response of RC members can be greatly influenced by the corrosion of longitudinal reinforcements and anchorage conditions, and the failure modes can be changed from the diagonal shear-tension to the bond-critical mechanisms. The proposed approach captured such unique behavioral characteristics of RC members with corroded longitudinal reinforcement. [ABSTRACT FROM AUTHOR]

Eccentric loading or compatibility conditions can cause beams in buildings to be subjected to significant torsions. Although design procedures for torsion are based on tests of stand-alone members and require closed stirrups to be used as transverse reinforcement, interior girders in beam-and-girder construction are usually integral with floor slabs and reinforced with open stirrups. This paper describes an experimental investigation of two post-tensioned companion specimens, designed to represent interior beams with an integral slab, which were loaded to failure under combined moment, shear, and torsion. The specimens were identical, except one was detailed using open stirrups and the other using closed stirrups. The strength of these members was significantly underpredicted by the ACI 318-19 and CSA A23.3-19 codes, which were, on average, conservative by factors of 3.50 and 2.05, respectively. The specimen detailed with open stirrups did not demonstrate a significantly different torsional response than the specimen containing closed stirrups. [ABSTRACT FROM AUTHOR]

Ultra-high-performance fiber-reinforced concrete (UHPFRC) possesses outstanding mechanical properties and high durability, and thus can provide effective retrofit solutions for concrete walls and wall-type bridge piers. This self-leveling material can be cast in thin layers around the pier to protect it from corrosive environments and to enhance its shear resistance. However, while this is a promising solution, research has focused mostly on the retrofit of slabs and beams. To address this gap in knowledge, this paper presents results from four large-scale tests of shear-critical concrete walls with and without UHPFRC jackets. The test variables are the thickness of the jacket, the preparation of the concrete surface, and the level of axial load. It is shown that water-jetting of the surface ensures an effective composite action of the concrete and UHPFRC, while a smooth surface results in early debonding. It is also demonstrated that, while the reference reinforced concrete specimen failed in brittle shear, water-jetted walls with 30 and 50 mm jackets reached their flexural capacity and exhibited enhanced crack control. In addition to test results, the study also proposes and validates a three-degree-of-freedom kinematic model to accurately describe the deformation patterns of UHPFRC-strengthened walls. INSET: 60. [ABSTRACT FROM AUTHOR]

This study investigated the friction shear behavior of concrete consisting of recycled aggregates and natural reinforced steel fibers. The concrete's natural aggregates were 50% substituted for recycled ones. The addition of steel fibers was evaluated in two different percentages in volume: 0.5 and 1.0%. Thus, 27 non-cracked push-off specimens were produced. The recycled aggregates were separated into two groups according to the strength of the original concrete: Group 1 (15 to 20 MPa) and Group 2 (35 to 40 MPa). Data analysis showed that the concrete's original strength and steel fiber percentage influenced the shear transfer capacity. Experimental data from natural concrete (NC) and high-strength concrete (HSC) with steel fibers tests performed using the push-off model and shear test methods were recompiled from the technical literature. Using models proposed by some researchers, it was concluded that both methods showed high dispersion in results. [ABSTRACT FROM AUTHOR]

According to traditional theory, there should be shear stresses in the cracked tension zone due to the presence of bond between longitudinal tension reinforcements and surrounding concrete. To investigate the effect of this bond mechanism on shear behaviors of prestressed concrete (PSC) members with and without shear reinforcement, the dual potential capacity model (DPCM) was adopted in this study. The size effect typically observed in large PSC members was also considered in the proposed method by addressing the shear crack concentration concept. Verifications of the proposed model were conducted using the extensive shear database of PSC members with various material properties and geometrical details. As an extreme case, the perfect-slip behavior (no bond condition) between a prestressing strand and surrounding concrete in unbonded post-tensioned (UPT) concrete members was considered in the proposed model, and their analytical results were used to identify how the bond mechanism affects the shear strengths and failure modes of PSC members. [ABSTRACT FROM AUTHOR]

The use of distributed fiber-optic strain sensors (FOS) has the potential to allow for reinforced concrete behavior to be quantified and understood with a new level of detail. In this investigation, three large reinforced concrete (RC) beams—JP-1, JP-2, and JP-3—with varying percentages of transverse reinforcement, were tested in three-point bending. Distributed FOS were installed on the longitudinal and transverse reinforcement bars, enabling identification and quantification of a number of behavioral mechanisms. These included stirrup demands at all depths and locations in the member, variations in longitudinal bar strain at the support based on shear demand, and bending of longitudinal bars from stirrup hook anchorage. After longitudinal bar yielding, the development and growth of a plastic hinge was monitored in specimen JP-3 under increasing plastic rotation. Simultaneously, the stirrup strains increased despite being subjected to a near-constant shear force, especially near the critical section for shear. [ABSTRACT FROM AUTHOR]

For the assessment of existing slab-between-girder bridges, the shear capacity and failure mode are under discussion. Previous research showed that the static and fatigue punching capacity of the slabs is sufficient as a result of compressive membrane action. The girders then become the critical elements. This research studies the shear capacity of prestressed concrete bridge girders. For this purpose, four (half) girders were taken from an existing bridge that was scheduled for demolition and replacement and tested to failure in the laboratory. Two loading positions were studied. The results show that there should be a distinction between the mode of inclined cracking and the actual failure mode. In addition, the results show that for prestressed concrete girders, the influence of the shear span-depth ratio should be considered for shear span-depth ratios larger than 2.5. These insights can be used for the assessment of existing slab-between-girder bridges in the Netherlands. [ABSTRACT FROM AUTHOR]

Six deep beams without transversal reinforcement made of sand-lightweight concrete and six deep beams made of sand-lightweight concrete with 1.0% of steel fibers were tested and compared with conventional concrete deep beams with and without fibers. The shear-span to deep beam height ratio (a/h) was 0.5, 0.8, and 1.0. The cross section heights were 400, 600, and 700 mm (15.7, 23.6, and 27.6 in.). The deep beams were tested to failure under a four-point bending test, using a hydraulic actuator with 500 kN (674 kip) capacity load cell. After testing, it was concluded that the shear-strength values were smaller in larger span deep beams. The presence of steel fibers increased the maximum strength and contributed quantify to the strength to diagonal cracking. The maximum shear load in steel fiber deep beams increased by approximately 16%. The size effect was more significant in sand-lightweight concrete deep beams. Besides, it was proposed a coefficient to validate the cracking strut-and-tie model (CSTM) to evaluate the applicability in deep beams of sand-lightweight concrete with and without steel fibers and the experimental maximum shear predictions are compared according to some codes for sand-lightweight concrete deep beams and by codes and some codes and researchers for sand lightweight concrete deep beams with steel fibers. [ABSTRACT FROM AUTHOR]

Deep concrete beams with shear span-depth ratios a/d ≤ 2.5 are used to resist large shear forces due to their ability to develop arch action. In high-rise buildings, deep transfer girders are typically loaded by discontinuous columns from multiple floors, while in bridges, deep pier caps support the girders of the superstructure. In these situations, prestressing is typically applied to limit the opening of cracks under service loads, but its favorable effect on the shear strength is either neglected or underestimated. This paper examines experimental evidence for the shear behavior of prestressed beams and proposes a kinematics-based model for predicting their strength and deformations at failure. It is shown that prestressing alters the crack patterns of concrete beams, and consequently results in the development of arch action in beams with a/d reaching 6 or 7. Therefore, the proposed model, which stems from a two-parameter kinematic theory for deep reinforced concrete beams, is extended and applied to prestressed test specimens with a/d varying from 0.55 to 6.73, producing adequate predictions of strength and deformations. [ABSTRACT FROM AUTHOR]

The behavior of reinforced concrete (RC) squat walls constructed with conventional- and high-strength materials was evaluated through tests of 10 wall specimens subjected to reversed cyclic loading. Primary variables included specimen height-to-length aspect ratio, steel grade, concrete compressive strength, and normalized shear stress demand. Specimens were generally in compliance with ACI 318-14. Test results showed that specimens containing conventional- and high-strength steel had similar strength and deformation capacities when designed to have equivalent steel force, defined as total steel area times steel yield stress. The lateral strength of walls with aspect ratios of 1.0 and 1.5 can be estimated using their nominal flexural strength when the nominal shear strength exceeds Vmn. For specimens with an aspect ratio of 0.5, the lateral strength was close to the force required to cause flexural reinforcement yielding and less than the nominal shear strength calculated per ACI 318-14. Specimen deformation capacity decreased as the normalized shear stress increased. The use of high-strength concrete, which led to a reduced normalized shear stress demand, resulted in larger specimen deformation capacity. [ABSTRACT FROM AUTHOR]

Given current environmental concerns, attention has been directed toward the use of recycled coarse aggregates (RCAs) as a substitute for natural raw materials commonly consumed in construction. In regard to shear performance, limited studies currently exist. To this end, a total of 56 reinforced concrete beams without stirrups were tested to identify the effect of using RCA on shear strength. Failure governed primarily by shear span-depth ratios and partially by tension reinforcement ratios can significantly affect shear behavior of RCA concrete members. Test results obtained for this study were evaluated using current ACI 318 shear design equations. Overall, crack patterns and failure modes for the RCA concrete test specimens were similar to those of natural coarse aggregates (NCAs). On this basis, it was established that RCA concrete beams can be used in practice with confidence in satisfactory shear performance. [ABSTRACT FROM AUTHOR]

In recent experiments, individual stretch length anchors were found to improve the tensile displacement capacity of conventional anchors under simultaneous cyclic tension and shear. Two quasistatic cyclic experiments were conducted on a 1:2.5 scale model of a dry storage cask (DSC) connected to the foundation using stretch length anchors with an eight-bar diameter (8db) stretch length. The cask was modeled using a circular steel cylinder. In the first experiment, the cask was grouted to the anchorage ring resulting in non-composite action between the cask and the “free-ring”; in the second experiment, the anchorage ring was welded to the DSC, resulting in composite action of the cask and “fixed-ring”. Both test configurations prevented horizontal sliding and toppling of the DSC. The free-ring configuration dissipated significantly more hysteretic energy compared to the fixed ring; however, this was accompanied by vertical movement of the cask. A model for individual stretch length anchors is proposed and is used to simulate the cyclic tests using finite element analysis with acceptable accuracy. [ABSTRACT FROM AUTHOR]

The simple detailing-based design recommendations for carbon fiber-reinforced polymer (CFRP) anchors presented herein were developed based on a database of 51 small-scale tests. The small-scale database indicated that a single CFRP anchor can develop the fracture strength of two layers of 10 in. (254 mm) wide CFRP strips if the anchor is properly detailed. Although CFRP strips are currently being designed for a maximum effective strain of 0.004, CFRP anchors should be designed to resist the full tensile capacity of the CFRP strips since the crack width distribution in a member can produce CFRP strains that exceed the maximum permitted effective strain. To achieve full CFRP material use, data shows that an anchor-to-strip material ratio (AMR) greater than 2.0 should be used. Additionally, the anchor holes should have a minimum chamfer radius that is 1.4 times the anchor hole radius to mitigate stress concentrations at the anchor bend. [ABSTRACT FROM AUTHOR]

Thick reinforced concrete members not containing shear reinforcement can fail at shear stresses significantly lower than those specified by the 2014 ACI Code. This is because the traditional ACI shear provisions were based on tests of small specimens, and do not account for the size effect in shear. This paper focuses on an experimental program in which a 4000 mm (13 ft) thick slab strip specimen and a 300 mm (12 in.) deep companion specimen were constructed and tested to failure. These tests extend the range of a series of 17 such slab strip experiments previously tested at the University of Toronto. The results show that the 2014 ACI Code can give dangerously high estimates of shear capacity for very thick slabs not containing shear reinforcement. The research also shows that minimum shear reinforcement greatly increases both the strength and deformability of thick slabs. [ABSTRACT FROM AUTHOR]

Shear capacity is an important strength parameter required in the design of concrete flexural members; its reliable estimation is one of the important requirements of the design process. However, unlike other mechanical properties of concrete, the shear capacity of concrete beams is a complex phenomenon. The inclusion of steel fibers in concrete further adds complexity to the shear capacity determination, albeit with an enhancement of the shear capacity. In the past, efforts have been made to model the shear response of steel fiber-reinforced concrete (SFRC) members, mostly in the form of empirical relations derived from the results of experimental studies. A theoretical formulation is presented herein to predict the shear capacity of the SFRC rectangular beams without web reinforcement. Its efficacy is also checked using results computed from available design guidelines, empirical relations, and experimental test data. A good correlation is found between the predicted and the available test results. [ABSTRACT FROM AUTHOR]

Russian SNiP code is dominantly adopted to design concrete structures through the so-called Eurasia countries. However, there has been no significant modification and update due to complex political and industrial situations in this region for the past several decades. In addition, it is very hard to trace back the origin and design philosophy of the shear design method specified in SNiP code due to limited access to important documents hidden in different engineering practices and industrial barriers. This study therefore addresses the exact background of the shear design method in SNiP code, and its accuracy and applicability were examined in detail by using the currently available shear databases for reinforced and prestressed concrete beam members. On this basis, the key influencing parameters of shear strengths in concrete members were identified, and the complex design procedures in the current SNiP code were modified to secure a reasonable safety level and better applicability. [ABSTRACT FROM AUTHOR]

This study was motivated by the observation of unexpected cracking in an actual reinforced concrete (RC) pier cap, consisting of a pair of two secondary corbels, supported on a primary corbel with the pier at its center. The pier cap was analyzed using the strut-and-tie method (STM) by considering a three-dimensional (3-D) model. Tests were carried out on two scaled-down pier cap specimens to assess safety and serviceability performance. The load-carrying capacity of the pier cap was under-predicted by approximately 75% by STM using ACI 318 and AASHTO codes. The test results presented in the paper include evolution of cracking and strains in the steel reinforcing bars, along with load-deflection plots. It was observed that concentrating reinforcing bars near the bearings resulted in an increase in strength by approximately 8.5% without adversely affecting serviceability. In summary, STM is found to provide an effective basis for the design and detailing of such complex pier caps. [ABSTRACT FROM AUTHOR]

The prestressed hollow-core slab (PHCS) system is one of the most commonly adopted precast concrete flooring systems, which can optimize productivity and structural efficiency. Because PHCS members are typically produced by the extrusion method in longline precast plants, it is extremely difficult to provide shear reinforcements due to the automated fabrication method for forming multiple hollow-cores in a cross section. However, the current ACI 318 building code stipulates that the web-shear capacity of hollowcore members over 315 mm (12.5 in.) thickness without minimum shear reinforcement should be reduced by half, which increases the demands of shear strengthening for a thick PHCS member at its end regions. In this study, the shear tests of thick PHCS members strengthened in shear, using various core-filling methods frequently used in the current precast industry, were conducted and a new analytical method was addressed to estimate the shear strengths of the PHCS members composite with core-filling concretes. [ABSTRACT FROM AUTHOR]

Fabric-reinforced cementitious matrix (FRCM) systems are becoming an excellent choice for the shear strengthening of reinforced concrete (RC) beams owing to their excellent structural performance and compatibility with the concrete substrate. There is a wealth of experimental research on the application of FRCM for shear strengthening of beams; however, there is a lack of research on assessing the performance of the beams theoretically. The primary objective of this research effort, therefore, is to propose a design equation to predict the shear capacity of FRCM shear-strengthened beams. The developed equation is based on the simplified compression field theory (SCFT) combined with probability and statistical techniques. The equation can be used for calculating the shear capacity of the FRCM shear-strengthened and unstrengthened beams. The equation accounts for the contributions of concrete, longitudinal tensile reinforcement, internal shear reinforcement (ISR), and FRCM. An extensive database of shear-critical RC beams has been used to validate the developed equation. It has been found that the proposed equation can predict the shear capacity of both unstrengthened and strengthened beams with reasonable accuracy. The prediction capability of the developed equation is compared with that of the ACI 549 guideline for the strengthened beams and the ACI 318-14, AASHTO-LRDF, and Eurocode 2 (2004) for unstrengthened beams. [ABSTRACT FROM AUTHOR]

The shear strength of beams and one-way slabs has been acknowledged for more than one century as one of the most complex, yet fundamental, topics to be addressed in structural concrete design. The experimental data used to investigate the phenomenon has traditionally been obtained from tests on simply supported beams subjected to point loading and recording only a limited amount of data (applied load and deflection in most cases). Following these experimental evidences, design formulas have been calibrated-- in many cases in an empirical manner--by using large amounts of experiments in the form of databases. Also, mechanical models have been proposed as a rational approach to shear design, which can be conceptually very different and relies on different sheartransfer actions. Discussions on the pertinence of these models are mostly based on the general agreement of the failure load to existing datasets more than on a critical review of their basic hypotheses. Within this context, the development of new measuring techniques, such as digital image correlation (DIC), enables a systematic and transparent examination of the shear crack development and of the role of the various potential shear-transfer actions. This allows for a scientific discussion on the correctness of the principles of the design approaches and allows understanding their pertinence and limitations. Based on these possibilities, the main hypotheses of the Critical Shear Crack Theory (CSCT) for shear design are examined in this paper. To that aim, the results of a specific test series on specimens tested under realistic loading conditions are reviewed. The results show that shear strength results from a combination of various shear-transfer actions depending on the development of shear cracks and their associated kinematics. On this basis, the applicability and pertinence of the CSCT main hypotheses are discussed and a complete mechanical approach is formulated. Also, it is shown that the CSCT can be formulated in a simple and consistent manner as closed-form design equations. [ABSTRACT FROM AUTHOR]

Modern spliced girder bridges consist of precast, pretensioned concrete girders joined together at cast-in-place (CIP) splice regions and made continuous through post-tensioning. Despite the growing use of spliced girders, relatively little research has focused on the behavior of the discontinuity created at the splice regions. An experimental program was conducted to study the strength and behavior of the CIP splice regions of spliced I-girders. The program focused on the shear behavior and shear failure mechanism of spliced girders containing post-tensioned CIP splice regions located within the span lengths of the girders. Two tests were conducted on large-scale spliced girder specimens. Large flexural demands permitted the flexural behaviors of the specimens to be evaluated as well. The test results revealed that the shear behavior of the spliced girder specimens was comparable to that of monolithically cast post-tensioned I-girders. [ABSTRACT FROM AUTHOR]

The tension capacity in cracked concrete is not well defined in existing shear models for reinforced concrete (RC) membrane elements under cyclic reversed loading, and the shear strength of RC elements is consequently overestimated due to the deviated decreasing branch of envelope of cyclic tensile stress-strain relationship. In this paper, the cyclic effect of limited tension stiffening of cracked RC elements is evaluated by proposing an analytical model named as the cyclic tension-stiffening fixed-angle truss model (CTFTM). The proposed model, based on fixed-angle theory, integrates unloading and reloading rules and accumulated damage into the limited tension-stiffening effect under cyclic loading and considers the consequent local stress variation at crack surface. The cyclic effect of limited tension stiffening of RC elements is verified by comparing with experimental results in the literature. The predictions show good agreement, and the effect of biaxial loading is also examined. [ABSTRACT FROM AUTHOR]

A large reinforced concrete (RC) beam designed to fail in shear was experimentally tested and monitored with distributed sensing technologies. Fiber-optic sensors (FOS) were used to monitor the strain along the flexural and shear reinforcement, and digital image correlation (DIC) was used to measure strains and displacements on the concrete surface. Measurements from the distributed sensing technologies were found to be in agreement with conventional sensors when tensile elongation and midspan deflection were analyzed prior to the development of extensive shear cracks. Results showed that cracking on the concrete surface was correlated with peaks in the FOS strain data for both the flexural and shear reinforcement. Combined distributed measurement (CDM) plots presented the full beam response at a given load. A method of monitoring the distributed shear strain was proposed and used to assess the behavior with increasing load and showed that prior to failure, approximately 45% of the beam displacement was due to shear strain. The presented measurement technique using FOS and DIC is shown to enable a more detailed study of shear failures, specifically, in a fashion that enables the quantification of the individual response of reinforcing steel and concrete under loading. [ABSTRACT FROM AUTHOR]

Pile caps used in foundations are commonly designed for simple cases of loading and geometry using the strut-and-tie method. This approach is known to provide safe designs and rather conservative predictions of the ultimate failure load of tests. This level of conservatism is due mainly to the large simplifications made in the geometry assumed, which in many cases ignore relevant parameters such as the size of the column. A three-dimensional (3-D) strutand- tie model is presented for four-pile caps in which the geometry adopted is optimized. The inclination of the direct strut from the column to the pile is obtained analytically through the maximization process of the resisting load carried by the truss assuming different modes of failure (flexural and shear). This approach is shown to provide more accurate predictions of the strength of existing deep pile cap tests with lower scatter compared to design approaches in the literature and the ACI 318 Code. [ABSTRACT FROM AUTHOR]

Relationships in ACI 318-14 for calculating the concrete contribution to shear resistance (Vc) in reinforced concrete (RC) members (that is, non-prestressed) have been replaced in ACI 318-19 by one general relationship that considers the combined effects of member depth, percentage of longitudinal reinforcement, and the effect of axial stress on predicted shear strength capacity. This new relationship is Vc = (8λsλ[ρw]1/3√fc′ + Nu/[6Ag])bwd, where λs is a size effect factor equal to √(2/[1 + d/10]) that accounts for a reduction in shear stress capacity with increasing member depth. The frequently used expression in ACI 318-14, Vc = 2λ√fc′bwd, may continue to be used in members containing at least the minimum level of shear reinforcement. The one-way shear provisions for prestressed concrete (PC) members were not changed in this code cycle. The primary basis for the new RC provisions are test results compiled in databases developed and analyzed over the past two decades through a collaboration of Joint ACI-ASCE Committee 445, Shear and Torsion, and the German Committee for Structural Concrete (DAbStb). The process for developing these new provisions included an invitation to the ACI community to suggest new one-way shear design provisions. These suggestions were discussed within Joint ACI-ASCE Committee 445, and then evaluated and modified by ACI Subcommittee 318-E, Section and Member Strength, with consideration of their basis, accuracy, safety, ease-of-use, and range of application. [ABSTRACT FROM AUTHOR]

Eight post-tensioned beams were tested at the University of Toronto to study the size effect in shear and the influence of different tendon layouts. The specimens varied in depth from 250 to 1000 mm (9.84 to 39.4 in.), while the unbonded tendons were either straight or harped. The eccentricity of the tendons was either zero, 1/6, or 1/2.67 of the section depth. The beams had no stirrups and were tested to shear failure under symmetrical three-point bending. It is shown that the specimens with a shear-span-to-effective-depth ratio of approximately 3 developed arch action and exhibited a size effect. A strut-and-tie model based on the AASHTO code captures the experimental results well, except the high shear resistance observed in the smallest specimens. To explain this behavior and the transition from slender to deep members, the paper sets the basis of a rational modeling approach based on kinematics. It is shown that the complete deformation patterns of the beams, including the width of the shear cracks, can be captured by a kinematic model with only three degrees of freedom. [ABSTRACT FROM AUTHOR]

The nonlinear analysis of reinforced concrete frame structures with slender members can be performed accurately and efficiently with one-dimensional (1-D) elements based on the plane-sections-remain- plane hypothesis. However, if the frame also includes deep beams which require two-dimensional (2-D) high-fidelity finite element procedures, the analysis of large structures can become very costly. To address this challenge, this paper proposes a mixed-type modeling framework which integrates 1-D slender beam elements with a novel 1-D macroelement for deep beams. The framework is implemented in an existing nonlinear analysis procedure and is used to model 18 deep beam tests and a 20-story frame. It is shown that the proposed modeling framework provides similarly accurate predictions to the 2-D high-fidelity procedures but requires a fraction of the time for modeling and analysis. Further-more, the macroelement improves the post-peak predictions, and therefore the framework is suitable for evaluating the resilience of structures under extreme loading. [ABSTRACT FROM AUTHOR]

Six one-way reinforced concrete slabs, simply supported along the short sides by means of corbels (dapped ends), were recently tested for bending and shear behavior in Milan under two different crosswise load distributions and with three partially different reinforcement layouts in the supporting corbels and in the main body (size 2200 x 1300 mm [7.22 x 4.27 ft]; thickness/length ratio close to 1/14; corbel depth and overhang/length ratio close to 1/23). The tests in bending under the service loads and in shear up to and beyond the peak load show that load crosswise-distribution plays a minor role. In shear, the quite complex crack patterns in the D-regions close to the dapped ends clearly indicate the formation of very effective strut-and-tie systems if the bottom bars of the main body are bent up, and of shallow arch-and-tie systems if the same bars are straight. In the former case, a proper introduction of the bond along the tension bars of the corbels is a must to define the position of bond-related joints and to make strut-and-tie models more reliable in predicting the bearing capacity, while in the latter case, the design equations provided by the codes for constantsection shear-unreinforced beams (ACI 318, EC2, and fib Model Code 2010) prove to be adequate also in the case of corbels. [ABSTRACT FROM AUTHOR]