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This study proposes a unified shear design provision for slender steel- and fiber-reinforced polymer (FRP)-reinforced concrete (RC) members. The proposed model is a modification of the ACI 318-19 model to include the axial stiffness of the longitudinal reinforcement by introducing a new modification term, nc, representing the elastic modular ratio of the longitudinal reinforcement to the concrete. The new relation is Vc = (0.4 [ncρfl]1/3 λs√fc' + Nu/[6Ag])bwd. The unified shear model was assessed with five experimental data sets: FRP-RC beams without shear reinforcement (288 beams), steel-RC beams without shear reinforcement (759 beams), FRP-RC beams with shear reinforcement (56 beams), steel-RC beams with shear reinforcement (157 beams), and steel-RC beams with axial force (prestressed) but without shear reinforcement (209 beams). The unified shear model provided better performance than the ACI 318-19 and ACI CODE-440.11-22 provisions in terms of mean, coefficient of variation, standard deviation (SD), and absolute average error (AAE). The unified model also showed improved performance over a wider range of material properties. In addition, reliability analysis using Monte Carlo simulation indicated that the unified shear model provides a consistent satisfactory safety level with a reliability index between 3.5 and 4.0 for both steel- and FRP-RC members. The reliability index provided by the unified model is similar to the reliability index provided by the ACI 318-19 shear provision. In contrast, the ACI CODE-440.11-22 results in highly conservative estimates with a reliability index between 4.5 and 5.0. [ABSTRACT FROM AUTHOR]

Carbon fiber-reinforced polymer (CFRP) is a widely used material for reinforced concrete (RC) beam strengthening. Because of exposure to severe environments and improper construction, CFRP sheets may separate from the bottom of RC beams. To analyze the influence of this type of interfacial defect on the mechanical properties of RC beams quantitatively and provide a reference for the rehabilitation of structures, this paper investigates the flexural properties of RC beams strengthened with partially bonded CFRP by experiments and analytical studies. To measure the degree of unbonded CFRP, a new parameter called the unbonded ratio was established, which is defined as the ratio of unbonded length to the total length of strengthening CFRP in the tension zone. Twenty-six RC beams were fabricated and tested in the present study, and the experimental variables were the unbonded ratio, thickness of the CFRP sheet, and anchorage method (vertical U-jacket, inclined U-jacket, and mechanical plate). The cracking load, ultimate load, load-midspan deflection curve, ductility, crack pattern, and failure modes of these specimens are discussed. Also, the coupling effect of the unbonded CFRP and anchorage method on the flexural performance of strengthened beams was investigated. Test results indicated that the ultimate load decreased with the increase of the unbonded ratio before the unbonded ratio reached its critical value. It was also found that the mechanical-plate anchorage and inclined U-jackets were superior to traditional vertical U-jackets in terms of load-carrying capacity and flexural stiffness and postponed the debonding of CFRP. Finally, a theoretical model for the ultimate load of RC beams strengthened with inclined U-jackets was proposed, which showed a good agreement with the test results. [ABSTRACT FROM AUTHOR]

Failure in beams reinforced with a small amount of transverse reinforcement is brittle due to reinforcement rupture after critical shear cracking occurs. To eliminate this problem, standards recommend formulas to calculate the minimum amount of transverse reinforcement in reinforced concrete structures. Reinforcement can resist loads after the first crack's appearance, preventing beam rupture from being brittle but making it somewhat ductile. This paper presents a theoretical experimental analysis to determine the minimum transverse reinforcement ratio in beams of high-strength ordinary portland cement concrete (BHSOPCC), low-strength ordinary portland cement concrete (BLSOPCC), and low-strength geopolymeric concrete (BLSGC). The beam dimensions were 150 x 450 x 4500 mm. They were subjected to a four-point bending test to assess shear failure. The transverse reinforcement ρsw,minfyk ranged from 0 to 1.16 MPa, in the ranges provided by ACI 318-19, AASHTO LRFD, fib Model Code, and ABNT NBR 6118:2014. This paper investigates the minimum shear reinforcement ratio for various types of concretes with different strengths and attempts to reevaluate the associated standards that have already been established. The parameter τwy*/τwcr proposed in this paper to define whether or not a beam has minimum transverse reinforcement is more appropriate. [ABSTRACT FROM AUTHOR]

The objective of the present study is to assess the flexural residual strengths of lightweight aggregate concrete (LWAC) reinforced with micro-steel fibers. Further, the material class of such concrete was examined through comparison with the fiber-reinforced concrete classification specified in the provisions of fib 2010. Fourteen beam specimens were classified into L (21 MPa [3.05 ksi]) and H (40 MPa [5.80 ksi]) groups according to the design compressive strength of LWAC. The volume fraction of micro-steel fibers varied from 0 to 1.5% at a spacing of 0.25% in each beam group. From the beam test results under the three-point loading condition, flexural stress-crack mouth opening displacement (CMOD) curves were measured and then discussed as a function of the fiber reinforcing index (βf). The flexural residual strengths corresponding to four different CMOD values (0.5, 1.5, 2.5, and 3.5 mm [0.02, 0.06, 0.1, and 0.14 in.]) were compared with previous empirical equations and fib 2010 classification. The various analyses of the measured results indicate that βf can be regarded as a critical factor in directly determining the magnitude of flexural residual strengths and assessing material classification. The proposed refined equations improve the accuracy in predicting the flexural residual strengths of concrete beams with different densities and reinforced with different types of steel fibers. Consequently, microsteel fibers are a promising partial replacement for conventional steel reinforcing bars to enhance the ductility of LWAC elements. [ABSTRACT FROM AUTHOR]

A database of results from 27 tests of diagonally reinforced concrete coupling beams was analyzed to develop improved force-deformation envelopes (backbone curves) for modeling and analysis of coupling beams. The database, which was selected from a larger set of 60 test results, comprises specimens that generally satisfy ACI 318-19 requirements. The analyses show that the chord rotation capacity of diagonally reinforced concrete coupling beams compliant with ACI 318-19 is closely correlated with beam clear span-to-overall depth ratio and, to a lesser extent, the ratio of hoop spacing to diagonal bar diameter. A simple expression is proposed for estimating beam chord rotation capacity. Coupling beam strength was shown to be more accurately estimated from flexural strength calculations at beam ends than other methods. Recommendations are made for obtaining more accurate backbone curves in terms of chord rotation capacity, strength, and stiffness. [ABSTRACT FROM AUTHOR]

Two shear-critical beams completely reinforced with glass fiber-reinforced polymer (GFRP) bars were constructed and tested in the current study. One beam was tested at room temperature and the second beam was subjected to accelerated thermal conditioning to simulate long-term behavior of GFRP-reinforced concrete (RC) beams, considering the recent climate challenges leading to increasing temperatures across the world. Conditioning of the beam was carried out at 50°C (122°F) for 4 months under 60% relative humidity while subjected to sustained load throughout the conditioning period. No significant change in behavior was observed because of the conditioning. Additionally, available models including code provisions (CSA S806, CSA S6, and ACI 440.1R) to estimate the shear strength of shear-critical beams were critically evaluated and discussed. It was noticed that the inclusion of a second-order equation to predict the shear contribution from concrete (Vc) seemed to improve the accuracy of the predictions. [ABSTRACT FROM AUTHOR]

This paper presents a novel framework to assess the reliability of externally bonded (EB) fiber-reinforced polymer (FRP)- strengthened steel-reinforced concrete (RC) beams by considering the spatial variation of concrete and concrete-FRP bond interface properties. The spatial variation is considered by developing resistance models using nonlinear stochastic finite element (FE) simulation, where the concrete properties are represented using three-dimensional (3-D) random fields and the concrete-FRP bond strengths are represented using two-dimensional (2-D) random fields. The framework was developed, automated, and applied to select configurations of RC beams strengthened using carbon FRP. A parametric analysis consisting of 3000 nonlinear stochastic FE models was performed to assess the effect of spatial variability on the reliability index of members designed using CSA S806, CSA S6, and ACI 440.2R. Analysis results verified the developed framework and indicated the sensitivity of analysis results to variations in the spatial properties of the considered beams. [ABSTRACT FROM AUTHOR]

Overlaying a reinforced concrete beam (RCB) with polymer cement mortar (PCM) is a strengthening method that improves flexural stiffness by the increasing sectional force. However, the reduction between bond strength and the reinforcement in PCM overlay at high temperatures results in an increase in flexural crack spacing. Therefore, the pullout force must be taken into account when estimating the flexural capacity of PCM-overlay RCBs. The experimental study aims to assess the flexural performance of PCM-overlay RCBs under three different environmental temperature conditions: 20, 40, and 60°C. Seventeen beams with varying reinforcement ratios in PCM are tested at the mentioned temperature levels. Experimental results indicate a decrease of approximately 6 to 13% in strength at elevated temperatures, which can be attributed to the reduction in bond strength of the reinforcement caused by the degradation of the PCM. Analytically, the strength reduction is calculated by determining the average crack spacing in the flexural zone. Therefore, the proposed average crack spacing method (CSM) predicts that the flexural strength is within ±10% limits of experimental observations. This method is more conservative than the conventional sectional analysis method (SAM). The average CSM can contribute to a safer design of PCM-overlay RCBs by preventing overestimated prediction of the ultimate strength at high environmental temperatures. [ABSTRACT FROM AUTHOR]

Reinforced concrete (RC) coupling beams can act as an efficient energy-dissipating fuse and force transfer element between RC shear walls in low- to high-rise buildings. To investigate the effect of different reinforcement layouts, amounts of confinement, and loading protocols on RC coupling beams, eight RC coupling beams with a span-depth ratio of 2.5 were tested with three parameters: 1) longitudinal or diagonal reinforcement layout; 2) full, two-thirds, or one-half the amount of confinement relative to ACI 318-19 requirements; and 3) seismic or wind loading protocols. The test results showed that: first, the nominal shear and upper-limit equations for diagonally RC coupling beams in ACI 318-19 may need to be improved, and it is also recommended to consider the contribution of confinement to shear strength; and second, because only minor cracks were observed under the wind with no significant damage, the experiment in this study can act as an example of structural verification for performance-based wind design. [ABSTRACT FROM AUTHOR]

This paper aims to analyze practical considerations in the design of glass fiber-reinforced polymer-reinforced concrete (GFRP-RC) beams based on the newly adopted ACI CODE-440.11-22, addressing strength, serviceability, and detailing criteria. A beam example was taken from the ACI Reinforced Concrete Design Handbook and redesigned using GFRP bars and stirrups to analyze the effect of changing the reinforcement type. In the first phase, the beam was designed as an over-reinforced member with high-modulus (Ef = 60,000 MPa) and low-modulus (Ef = 44,815 MPa) GFRP bars. In the second phase, a parametric study was carried out to analyze the impact of changing key design parameters--namely, bond factor kb, concrete compressive strength fc', and the maximum deflection limit. GFRP-RC beams require more reinforcement area compared to conventional steel-RC, which may result in bar congestion. Current Code provisions related to detailing in particular are based on conservative assumptions due to a lack of experimentation and greatly penalize the design of GFRP-RC beams. The current Code provisions for development length, bar spacing, skin reinforcement, and stress at service make GFRP-RC design challenging. [ABSTRACT FROM AUTHOR]

A multi-angle truss model is proposed based on the optimal load paths of corroded reinforced concrete (CRC) beams. The load paths of CRC beams at the ultimate limit state, considering various corrosion levels, shear span-depth ratios, stirrup ratios, and loading methods are first studied. The load paths incorporating multiple variable-inclination struts can realistically describe the force-transfer mechanisms of CRC beams under flexure-shear interaction. The limiting failure criteria of the proposed truss model are then presented to estimate the shear capacity of CRC beams. Finally, the proposed model is verified by comparing with the experimental results of uncorroded and corroded reinforced concrete (RC) beams. Results show that the proposed model can reasonably predict the shear capacity and failure mode of CRC beams. For CRC beams at the ultimate limit state, corrosion damage has a negligible influence on the trajectory of load paths. The load paths change with the increase of the shear span-depth ratios of CRC beams. [ABSTRACT FROM AUTHOR]

This paper presents the feasibility and relevance of cementitious resins as bonding agents for near-surface-mounted (NSM) carbon fiber-reinforced polymer (CFRP) strips. Contrary to conventional organic matrixes, such inorganic resins offer promising performance when subjected to aggressive environments, especially under thermal distress. Three emerging resins are employed (polyester-silica, ultra-high-performance concrete [UHPC], and geopolymer) to strengthen reinforced concrete beams alongside NSM CFRP. After stochastically simulating various levels of pitting corrosion for a period of 100 years, the outcomes are represented in the beams by reducing the cross-sectional area of steel reinforcement before applying the rehabilitation system. The emphasis of experimental investigations lies in the workability of those resins and the flexural response of the retrofitted beams. Material-level testing reveals that the rheological properties of the resins are not related to their compressive strength. As far as load-carrying capacity is concerned, the beams bonded with polyester-silica outperform the beams with other resins; however, UHPC enables stable degradation over the years. The interfacial characteristics of the resins dominate the mechanical interaction between the damaged internal reinforcing steel and CFRP, thereby altering the tendency of capacity drops, post-yield plateaus, and crack distributions. Through analytical modeling, the provisions of existing design guidelines are evaluated, and a modification factor is suggested to promote the cementitious resins for NSM CFRP. [ABSTRACT FROM AUTHOR]

The conversion of material density during nonlinear topology optimization (NTO) results in the excessive distortion of minimum-density elements. An automatic stiffness adjustment technique is first proposed to overcome numerical instability. A multiproportional growth strategy of the minimum-density element stiffness is given according to the change of maximum strain. On this basis, a generation method of optimal load paths for corroded reinforced concrete (CRC) beams is presented by considering material properties loss and bond degradation. The design sensitivity in the form of corrosion-damaged strain energy is then derived based on the adjoint variable method. Finally, the effectiveness of the proposed method is illustrated by numerical examples. The load paths of CRC beams under various corrosion levels are studied. Results show that the proposed method can reasonably generate the load paths of CRC beams without the numerical instability. [ABSTRACT FROM AUTHOR]

This study investigates the flexural behavior and serviceability performance of lightweight self-consolidating concrete (LWSCC) beams reinforced with basalt fiber-reinforced polymer (BFRP) bars. Eleven reinforced concrete beam specimens with a crosssectional width and height of 200 mm (7.87 in.) and 300 mm (11.81 in.), respectively, and with a total length of 3100 mm (122.05 in.) were tested under a four-point bending load up to failure. Nine specimens were made with LWSCC, while the other two were made with normalweight concrete (NWC) as reference specimens. The test parameters were concrete density (LWSCC and NWC), reinforcement type (sand-coated BFRP, helically grooved BFRP, thread-wrapped BFRP, or steel), and longitudinal BFRP reinforcement ratio. The test results indicate that the LWSCC yielded lower beam self-weight (density of 1800 kg/m3 [112.4 lb/ft3]) than the NWC. Increasing the BFRP reinforcement ratio increased the normalized moment capacity of the LWSCC specimens. The test results were compared from the standpoint of the cracking and ultimate moment, deflection, and crack-width design provided in the available design standards for FRP-reinforced elements. The comparison indicates that the experimental moment capacities of the LWSCC and NWC beams were in good agreement with the predictions based on design standards with an average accuracy of =90%. The crack width of the LWSCC beams was affected by the surface configuration of the BFRP bars, while the deflection was not significantly affected by the concrete density. The Canadian design code yielded accurate predictions with a bond-dependent coefficient of 0.8 and 1.0 for the sand-coated and helically grooved BFRP bars, respectively, in the LWSCC. [ABSTRACT FROM AUTHOR]

Past studies had shown that welded wire reinforcment (WWR) can be used as an effective alternative to stirrups in resisting shear in reinforced concrete beams. Such a form of reinforcement reduces labor, decreases the time required to assemble the steel cage, and eliminates anomalies in the fabrication and placement of the stirrups. This study investigated the flexural behavior of reinforced concrete beams transversely reinforced with closed steel cages made by cold-formed WWR sheets. To accomplish the goals of the study, seventeen 2 m (6.6 ft) long beams with 200 x 300 mm (8 x 12 in.) cross sections were tested under a two-point load configuration with consideration of 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.]), and longitudinal steel reinforcement ratios (0.77 and 1.92%). A comparison between the test results of WWR-reinforced beams and their equivalent stirrup-reinforced beams was performed. The experimental study was accompanied by a theoretical component using the flexural design provisions in ACI 318. Compared to corresponding beams having stirrups equivalent to the vertical wires of the WWR, the WWR-reinforced beams had on average 20% more flexural capacity, just about the same stiffness at service load, and 10% less flexural ductility. The average experimental-to-nominal flexural capacity based on ACI 318 for concrete beams reinforced with WWR is equal to 1.15, which indicates that the Code can be reliably used to predict the bending moment capacity of such beams. The study recommends always using longitudinal reinforcing bars in WWR-reinforced beams and not relying solely on the longitudinal wires of the WWR for resisting flexure. [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]

Near-surface mounting (NSM) and external bonding (EB) are wildly used techniques for strengthening reinforced concrete (RC) beams using fiber-reinforced polymer (FRP) reinforcement. However, there are a few drawbacks to the use of these two techniques, including premature failure due to concrete cover separation (CCS), which can cause significant challenges for their wide practical applications. Hence, his experimental study investigates the efficiency of using a novel anchoring system for RC beams strengthened at the sides using NSM glass-FRP (NSM-GFRP) bars. The NSM-GFRP bars were anchored with either GFRP channels or GFRP channel strips. The experimental results showed that RC beams strengthened with side NSM-GFRP bars anchored with GFRP channels and GFRP channel strips increased the flexural load of the RC beams by 152% and 106%, respectively, compared to the unstrengthened reference beam. In addition, GFRP channel strips prevented the CCS failure and improved the ductility of the RC beam, using the full strength of NSM-GFRP bars. [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]

Robust numerical representation of the behavior of reinforced concrete (RC) shear walls under simulated earthquake action is critical to support an accurate evaluation of the performance of concrete buildings. Reliable damage predictions of concrete shear walls are also essential to understand the response of components attached to walls via anchors. Previous studies have shown that anchor load capacity is reduced in the presence of concrete damage. Accordingly, current U.S. building code requirements prohibit anchor installation in sections of walls where yielding of the reinforcement is expected. The aim of this requirement is to minimize the potential for anchorage failure during a seismic event. Identification of concrete damage in shear walls of varying characteristics is therefore relevant to anchor performance. In this regard, the present paper describes a parametric study performed using a multiple vertical-line element model able to couple shearflexure interaction. The aim of the study is to qualitatively identify regions of severe damage in concrete shear walls of varied geometric and detailing characteristics and thus better assist engineers in adhering with current code requirements. Results show that the regions where large damage is expected define a plastic hinge length and include the boundary elements in slender walls and the diagonal compression struts in squat walls. This information is used to suggest anchor installation locations to assure their robust performance when attaching nonstructural components and systems to RC shear walls subject to seismic loading. [ABSTRACT FROM AUTHOR]

This paper presents the effectiveness of structural retrofit for reinforced concrete beams containing variable steps. A strengthening system, consisting of externally bonded carbon fiber-reinforced polymer (CFRP) sheets and ultra-high-performance concrete (UHPC) infills, is proposed to improve the flexural response of the stepped beams alongside mitigated stress concentrations at the reentrant corner. Incorporating a step size ranging from 20 to 60% of the effective depth, unstrengthened (CONT) and strengthened groups are tested with and without anchorage: plain CFRP (CF), U-wraps (CFU), and U-wraps plus mechanical fasteners (CFUM). The bond between UHPC and a concrete substrate gradually grows up to 2.5 MPa (362 psi) at 28 days, accompanied by the improved certainty of adhesion. The load-carrying capacity of the strengthened beams increases by more than 23.1% relative to their unstrengthened counterparts; however, the efficacy of the retrofit system decreases with the incremented step size, which alters the failure characteristics and energy dissipation of those beams. According to analytical investigations, the asymmetric stress distribution of CFRP resulting from the geometric discrepancy is responsible for the progression of damage in the direction of the reduced section. The implications of concrete strength are insignificant for the development of interfacial stresses between the CFRP and UHPC, while the elastic modulus and application thickness of the CFRP and bonding agent dominate the magnitude of the stresses. Implementable recommendations are proposed for practice. [ABSTRACT FROM AUTHOR]

An efficient structural system for tall buildings to resist earthquake and wind loads consists of reinforced concrete structural walls linked by coupling beams, where the coupling beams act as the primary fuses to limit force demands on capacity-protected elements and actions and provide reliable energy dissipation mechanisms. Penetrations (openings) horizontally through coupling beams are often needed to accommodate piping and cables—for example, into a concrete elevator core, which could potentially have adverse impacts on coupling beam performance. ACI 318-19 is silent on whether penetrations are permitted or not, and if penetrations are needed, there are no provisions on the size and location of penetrations and the additional detailing needed at the penetration regions, primarily due to the lack of experimental data. To address this issue for diagonally reinforced concrete coupling beams, this study reviews data from six Japanese experimental programs that include results on 18 coupling beams with diagonal reinforcement and penetrations. The findings indicate that the penetration size and the detailing in the penetration region play an important role in the seismic performance of the beams. Recommendations are proposed on the location and size of penetrations and the additional detailing of the penetration region such that they do not adversely impact the seismic performance of the coupling beam. [ABSTRACT FROM AUTHOR]

The need for environmentally friendly alternatives to portland cement (PC) concrete has led to increasing interest in alternative cements. The study presented in this paper compared the shear strength, long-term compressive strength, and carbonation in belitic calcium sulfoaluminate (BCSA) cement and PC concrete beams. A total of twelve 8 ft long beams were made: eight BCSA cement concrete beams and four PC concrete beams tested at various ages. Year-old specimens were stored outside until they were tested. Cross sections were cut from the 1-year beams, and the pH was tested to determine carbonation depths. The BCSA cement concrete beams had similar shear strengths and behavior when compared to the PC concrete beams, and code equations were generally conservative for both cements. No visible carbonation was detected in either material after 1 year outdoors. Compressive strengths of cores showed increased strength over time in BCSA cement concrete, similar to PC concrete. [ABSTRACT FROM AUTHOR]

This study presents the use of V-M interaction diagrams to estimate the ultimate shear and moment demands of reinforced concrete (RC) beams. The method of analysis presented can be beneficial for both design and analysis as it provides a visual aid for gaining clearer insight into the determination of the maximum load-carrying capacity of a considered section, as well as its failure mode. To simplify the construction of such V-M interaction diagrams and remove the often-needed iterative procedure, the current American Association of State Highway and Transportation Officials (AASHTO) shear sectional design model based on the Modified Compression Field Theory (MCFT) was modified. As a result, the simplified process uses the strains of flexural reinforcement and moment demands at three events, which can be obtained by a simple elastic analysis. The maximum shear strengths were predicted for 1012 RC beams without transverse reinforcement using two current AASHTO shear design methods and the proposed simplified method. Overall predictions at failure from the V-M interaction diagram approach for all three methods showed great agreement with the test results with a reasonable coefficient of variation. Further investigation of the experimental variables revealed an overly conservative trend in beams with smaller effective depth and a/d ratio due to insufficient consideration of size effect and arch action. The noticeable trend by a/d ratio was somewhat moderated in the proposed method. Although the proposed method showed the most accurate predictions compared to the two AASHTO methods, an unconservative aspect existed for many cases so that a strength reduction factor of 0.75 was suggested. Also, the current strength reduction factor of 0.9 in AASHTO for shear was evaluated and considered appropriate. Given the satisfactory performance in estimating the maximum shear capacity, the proposed simplified AASHTO method using the V-M interaction diagram can serve as an alternative shear strength design and analysis method for slender RC beams. [ABSTRACT FROM AUTHOR]

Although the bond strength between reinforcing bars and pre-damaged concrete affects the seismic performance of repaired concrete structures, few studies have focused on the bond performance between the reinforcing bar and pre-damaged concrete. In the present study, to evaluate the effect of retrofitting with carbon fiber-reinforced polymer (CFRP) or ultra-high-performance concrete (UHPC) on the bar bond strength, lap-splice tests were performed on 20 beam specimens. The beam specimens were pre-damaged until bond failure or reinforcing bar yielding, and then the retrofitted beam specimens were reloaded to evaluate the bond strength recovery. Specimens were divided into five groups according to the reinforcing bar diameter, use of stirrups along the splice length, and type of preloading. Four retrofitting methods— CFRP sheet (C), a combination of CFRP sheet and crack injection epoxy (CE), UHPC (U), and a combination of CFRP sheet and UHPC (CU)—were applied to each group after preloading. The test results showed that the bar bond strength was improved by the used retrofitting methods, particularly by the retrofitting method of CU. In the specimens with a 20 mm reinforcing bar diameter and slight pre-damage, the retrofitting methods of C and CE were appropriate to restore the bar bond strength. For the specimens with a 28 mm reinforcing bar diameter and serious pre-damage, the bar bond strength was improved by retrofitting with U and CU. To consider the effects of pre-damage and retrofitting with CFRP sheet and/or UHPC on the bar bond strength, a modification of the existing methods for bar bond strength was proposed. The proposed method predicted the test results well. [ABSTRACT FROM AUTHOR]

This paper develops reliability-based design provisions for flexural strength of reinforced concrete (RC) beams with hybrid arrangements of fiber-reinforced polymer (FRP) and steel reinforcements. Firstly, three flexural failure modes of the hybrid RC beams were distinguished through balanced reinforcement ratios, and closedform solutions for the flexural strength were proposed. Based on the Monte Carlo simulation technique, probabilistic analyses of flexural failure modes were conducted to determine the minimum and maximum flexural reinforcement ratios for the hybrid beams. The first-order second-moment method was then applied to calibrate strength reduction factors to meet uniform target reliability level, βT = 3.5. Sensitivity analyses were performed to identify the most important parameters that influence the reliability indexes, indicating that the reliability of the hybrid FRP-steel RC beam decreased with the increase of the reinforcing index χ. As a result, this study recommended flexural strength reduction factors of (0.9 to 0.15χ) for the hybrid reinforced beam to achieve the target reliability index of 3.5. [ABSTRACT FROM AUTHOR]

Integrating glass fiber-reinforced polymer (GFRP) bars into lightweight self-consolidating concrete (LWSCC) would effectively contribute to producing lighter and more durable reinforced concrete (RC) structures. Nonetheless, the shear behavior of GFRP RC structures cast with LWSCC has not yet been fully defined. This paper reports experimental results on the behavior and shear strength of LWSCC beams reinforced with GFRP bars. The beams measured 3100 mm (122.05 in.) long, 200 mm (7.87 in.) wide, and 400 mm (15.75 in.) deep. The test program included six beams reinforced with GFRP bars and one control beam reinforced with conventional steel bars for comparison purposes. The test variables were the reinforcement type and ratio and concrete density. The experimental results indicate that using LWSCC allowed for decreasing the self-weight of the RC beams (density of 1800 kg/m3 [112.4 lb/ft3 ]) compared to normalweight concrete (NWC). All beams failed as a result of diagonal tension cracking. Increasing the axial stiffness of the longitudinal GFRP reinforcing bars improved the concrete shear capacity of the LWSCC beams. The test results of this study and the results for 42 specimens in the literature were compared to the current fiber-reinforced polymer (FRP) shear design equations in the design guidelines, codes, and literature. Applying concrete density reduction factors of 0.8 and 0.75 in the ACI 440.1R-15 and CSA S806-12 shear design equations, respectively, to consider the influence of concrete density achieved an appropriate degree of conservatism equal to that of the equations for NWC beams. [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]

In this research, novel functionally graded concrete deep beams without transverse reinforcement for transfer girder applications were constructed with varying shaped embedded high-strength struts surrounded by low-cement content concrete. The cement content in the low-cement content concrete also varied, with a maximum total beam cement reduction of 47% compared to the control. The placement method also varied, further revealing issues with fresh-on-hardened concrete casting. The beams were tested in three-point bending and monitored using distributed fiber-optic sensors (DFOS) and digital image correlation. The results of the tests revealed that diagonal-shaped embedded struts designed for three-point bending had the highest load capacity increase of up to 26%. However, using shapes not compatible with three-point bending resulted in load capacity decreases. DFOS also enhanced the understanding of strut-and-tie mechanisms, allowing for the visualization of the strain distribution in struts and quantifying formations of the strut and tie. [ABSTRACT FROM AUTHOR]

Ultra-high-performance concrete (UHPC) has been gradually used in structural engineering due to its excellent mechanical performance; however, predicting the shear strength of UHPC beams is still a challenge, especially for beams with small shear span-depth ratios. To address this issue, this paper is devoted to developing a rational model to predict the shear capacity of UHPC beams with stirrups. The shear-resisting mechanism of UHPC beams has been revealed and the contributions of compression zone and dowel action on shear strength have been presented. Combined with the Modified Compression Field Theory (MCFT), a simple method for shear capacity assessment has been presented. Twelve UHPC beams were designed and tested to validate the proposed model. The proposed method has been verified and can be used to predict the shear capacity and average diagonal crack width of UHPC beams with satisfactory accuracy, while the current design codes, including SETRA-AFGC and SIA, give conservative shear strength for UHPC beams when the shear to span is less than 2.5. Moreover, the contributions of compression zone and dowel action are found to be 32 and 17% for UHPC beams with small shear span-depth ratios. [ABSTRACT FROM AUTHOR]

In this study, the flexural fatigue performance of reinforced concrete (RC) beams strengthened with a fiber-reinforced polymer (FRP) grid-reinforced engineered cementitious composite (ECC) matrix was experimentally investigated. An FRP grid-reinforced ECC matrix (FGREM) composite strengthening layer was applied by reinstating the original concrete layer to a predetermined depth. The load level, FRP grid type, and strengthening amount were considered as test variables. The ultimate fatigue failure of the strengthened beams was found to be governed by the fracture of tensile steel bars. However, premature end debonding could be triggered in specimens subject to excessive strengthening. Furthermore, the fatigue life of the strengthened beams was distinctively improved owing to the relieved tensile stress range of the steel reinforcements. By relieving the damage accumulation of the constituent materials, this strengthening system can effectively ameliorate cracking, which is of great significance to the degeneration of stiffness and the development of deflections. [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]

The behavior of shear studs affect load transfer between the steel girder and the concrete deck. This aspect of behavior has vital importance in the evaluation of redundancy for composite steel bridges with fracture critical members (FCMs) in which the fracture of a member is being evaluated. It is important to include proper shear stud properties which cover the shear, tensile, and combined shear and tensile behavior to prevent erroneous conclusions when evaluating the redundancy of such bridges. In this study, a shear stud damage methodology was developed by calibrating finite element (FE) analysis to existing experimental data and other methodologies. The numerical results from FE models were used to develop new modification factors for the existing methodologies and develop an approach to more accurately model the strength, stiffness, and ductility of stud damage behavior for a range of typical shear stud, haunch, and flange configurations. [ABSTRACT FROM AUTHOR]

This research studies the effect of glass fiber-reinforced polymer (GFRP) bars as compressive reinforcement in reinforced concrete (RC) beam members. Three singly and six doubly reinforced GFRP-RC beams were tested under a four-point loading configuration. The effect of compressive reinforcement on the load-bearing capacity, ductility, stiffness, and failure mode is determined. Also, the compressive performance of GFRP bars is evaluated by testing GFRP-RC cylinders. According to the results, GFRP bars in compression had a limited contribution to enhancing flexural strength, and the maximum increment in the flexural capacity of doubly reinforced beams compared to singly reinforced specimens was 5%. GFRP-RC cylinders demonstrated a similar pattern, as the maximum strength increase compared to control specimens was 8%. Based on the evaluation of GFRP behavior, the contribution of bars in compression is limited due to the maximum strain that concrete withstands under compression. Considering the singly reinforced specimens, due to the presence of compressive GFRP bars, the stiffness of the doubly reinforced beams was reduced (up to 16%); however, the curvature and ductility were increased (up to 10% and 35%, respectively). In the end, a method based on deformations at the near-peak and peak load capacity was proposed to calculate the ductility of beams. The method predicts ductility enhancement due to compressive bars, as was observed in experiments, and also makes a distinction on failure modes. [ABSTRACT FROM AUTHOR]

Results from an experimental program consisting of 10 large beams are presented herein that investigated the behavior of reinforced concrete (RC) beams reinforced with glass fiber-reinforced polymers (GFRP) bars, before and after thermal conditioning. All the beams were completely reinforced with GFRP bars. Control beams tested at room temperature were designed to investigate the flexural behavior of the most-recent generation of GFRP straight bars as well as stirrups. Thermal treatment was designed to study the long-term durability of GFRP-RC beams considering the recent climate challenges of continuously increasing temperatures across the North American regions. Beams were conditioned at 50°C for 4 months under 60% relative humidity and were subjected to sustained load throughout the conditioning duration. Test results of the control beams showed that GFRP-RC beams can show significant increase in the ultimate failure load when appropriately confined in the flexure zone with transverse reinforcement. Deterioration of beams’ behavior was studied as a result of thermal conditioning, especially for stages related to concrete crushing as well as ultimate failure. Under-reinforced beams designed to fail in bottom bars’ rupture showed approximately 22% reduction in the ultimate failure load due to conditioning, but over-reinforced beams did not observe substantial reductions in the ultimate capacity although the load corresponding to initiating of concrete crushing reduced by approximately 10%. [ABSTRACT FROM AUTHOR]

Concrete loses its tensile resistance at crack interfaces in reinforced concrete beams but still can carry tension between two cracks, which is defined as tension stiffening. To model the stiffening effects on structural serviceability, an effective tension section was introduced based on homogenized average strain distributions in existing methods. However, the strain distribution of concrete gradually changes near the cracks. To calculate the effective section exactly, an alternative method is proposed by considering the gradual distribution. First, the gradual change in the tensile strains is modeled based on the crack location and depth and the internal force equilibrium is adopted to find a solution to the strain distribution along the height of cross sections. Then, based on the neutral axis and tensile force of the distribution, the area of the effective tension section is calculated. The effectiveness of the proposed method was validated using experimental data from reinforced concrete beams. The results show that the concrete strains of the cross sections changed from the obviously nonlinear distribution to approximately linear distribution according to the distance to cracks, which caused the neutral axes and effective tension section to change with the cracking pattern. The effective section reached its local minimum at every crack and the minimum would become smaller the deeper the crack. The proposed method could predict these changeable distributions and effective sections without introducing any additional simplification. The effective section could be used to assess the instantaneous deflection of the beams, whose calculated results were in good agreement with the experimental data but its application to the prediction of long-term responses should be further studied. [ABSTRACT FROM AUTHOR]

Six full-scale beams using either only steel bars, mixed steel bars and seven-wire steel strands, or only seven-wire steel strands as longitudinal reinforcement were tested under four-point bending. The bars were ASTM A706 Grade 60 (420 MPa) steel deformed bars, and the strands were ASTM A416 Grade 270 (1860 MPa) seven-wire steel strands. Test results showed that average crack spacing and width increased, while equivalent stiffness, flexural overstrength, and ductility decreased with increasing replacement of bars with strands. The decrease in ductility was mainly due to the reduced strain capacity of strands in tension and earlier buckling (bulging) of strands in compression compared to bars. The equivalent stress block method with the proposed models for strands provided conservative predictions for all the beams. The moment-curvature analysis method with the proposed models for strands produced moment-curvature relationships fairly close to measured responses, including the flexural overstrength and the failure mode. [ABSTRACT FROM AUTHOR]

This study uses machine learning (ML) to characterize the shear strength of reinforced concrete (RC) beams and one-way slabs. A database of 1436 RC shear tests is used to train three ML algorithms (ordinary linear regression, support vector regression, and Gaussian process regression). The database is divided into two training subsets per ACI 318-19 minimum shear reinforcement requirements. Each training sample consists of up to 10 predictive features (geometry, materials, reinforcement detail, load location) and the corresponding target feature (shear strength). The most accurate algorithm, the Gaussian process regression, has 17% and 11% smaller mean percent error in shear strength predictions than ACI 318-19 guidelines for the subsets with shear reinforcement areas less than and larger than the minimum ACI 318-19 requirement, respectively. This algorithm also provides predictive confidence with a standard deviations less than 5.2 kN (1.18 kip) for 99.7% of the predictions. [ABSTRACT FROM AUTHOR]

To investigate the shear behavior of post-tensioned concrete beams with fiber-reinforced polymer (FRP) reinforcements, a total of seven large-scale post-tensioned beams, with a total length of 5000 mm and a shear span-depth ratio of approximately 3.0, were tested to failure. Each beam was longitudinally reinforced with carbon FRP (CFRP) tendons and non-prestressed glass FRP (GFRP) bars. One reference beam had no stirrups and six beams were reinforced with GFRP stirrups. The test variables included the type (closed tie and continuous rectangular spiral) and ratio of GFRP stirrups. The diagonal crack width was obtained using digital image correlation. It was found that the beams with the highest shear GFRP reinforcement ratio of 0.47% failed in flexure, while the rest of the beams failed due to shear compression. The presence of GFRP stirrups had a slight effect on the flexure-shear cracking force, while it can efficiently restrict the development of shear cracks. The beams with GFRP tie ratios of 0.24% and 0.32% exhibited 6.6% and 13% increased shear capacity with respect to the beams without stirrups, respectively. The use of rectangular spiral GFRP shear reinforcement was highly favorable for enhancing the shear capacity [ABSTRACT FROM AUTHOR]

Structural lightweight-aggregate concrete (LWAC) has gained a broad range of applications in the construction industry owing to its reduced dead load and enhanced fire resistance. In this study, the potential of using lightweight expanded clay aggregates as a partial replacement for fine and coarse natural aggregates was experimentally and numerically examined. Testing was performed on cylindrical specimens made of normalweight and lightweight concrete incorporating microsilica as a partial replacement for cement to determine the associated stress-strain behavior. Subsequently, three-point bending testing was conducted on reinforced concrete beams to evaluate their structural behavior. Four levels of temperature were considered: 25°C (ambient temperature), and 250, 500, and 750°C (elevated temperatures). The finite element method through Abaqus software was deployed to numerically investigate the behavior at elevated temperatures through a comprehensive parametric study. The experimental and numerical results indicate that under high-temperature exposure, LWAC outperforms its normal counterpart in terms of strength, stiffness, and Young's modulus. It is also noticeable that LWAC beams retained their load-bearing capacity better than normalweightaggregate concrete (NWAC) after reaching the peak load. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental study on the comparative response of polypropylene (PP) fiber-incorporated reinforced concrete (RC) beams under fire conditions. Five fullscale RC beam specimens, made with different batch mixtures comprising normal plain concrete (NPC) and fiber-reinforced concrete (FRC), were tested to assess their spalling performance and structural behavior under fire conditions. The main variables in the experiments were the amount and length of PP fibers. Deflections, temperatures, and spalling in the beams were monitored during fire exposure. FRC beams' flexural failure occurs after 151 minutes at heating temperatures beyond 850°C, when deflections exceed span/20. When the concrete contains PP fibers (that is, FRC beams), the gamut of fire-induced spalling in RC beams gets reduced, increasing the fire resistance from 147 to 171 minutes (approximately 17%). Furthermore, test results show that adding 2 to 3 kg/m³ of PP fibers effectively releases the pore pressure through tensile cracking and reduces the amount of spalling in the FRC beams. [ABSTRACT FROM AUTHOR]

This study evaluated the shear strength of a diagonally reinforced coupling beam with steel fibers subjected to cyclic loading through experiments. A total of seven specimens were examined using the amount of transverse reinforcement, concrete strength, and volume fraction of steel fiber as variables. The experiments showed that sufficient ductility and strength were ensured even when steel fibers were incorporated and transverse reinforcement was simplified. In particular, with a 2% volume fraction of steel fibers, the strength and ductility satisfied ACI 318-19 because steel fiber-reinforced concrete sufficiently replaced the transverse reinforcement to prevent buckling of the diagonal reinforcing bars. When evaluating the shear strength of steel fiber-reinforced coupling beams with regard to the ACI provision, the shear strength was predicted more accurately when the shear contribution of the concrete was considered and the diagonal reinforcement was properly confined. [ABSTRACT FROM AUTHOR]

Under earthquake load, as the inelastic deformation increases, the shear strength of reinforced concrete coupling beams is degraded by diagonal cracking. In the present study, for the performance- based design of short coupling beams (l/h ≤ 2.5), a shear strength degradation model based on diagonal strut and truss mechanisms was developed, addressing the effects of the target chord rotation, longitudinal reinforcing bar ratio, length-to-height ratio, ratio and details of transverse reinforcement, distributed longitudinal web bars, and diagonal bars. Based on the proposed method, a simplified moment-rotation relationship of plastic hinges was developed for the nonlinear numerical analysis of coupling beams. For verification, the proposed method was applied to existing coupling beam specimens with a conventional reinforcing bar layout, distributed longitudinal web bars, and/or diagonal reinforcement. The predicted moment-rotation relationships generally agreed with the test results. Thus, the proposed plastic hinge model is applicable to the nonlinear analysis of short coupling beams to describe the shear strength degradation after flexural yielding. Design recommendations for the practical application of the proposed method were discussed. The proposed model revealed that the use of distributed longitudinal reinforcement and diagonal reinforcement is effective for high ductility. [ABSTRACT FROM AUTHOR]

Sixteen shear-critical reinforced concrete short beams (RCSB) with different percentages of tension reinforcement were loaded until failure at ambient and after 350, 550, and 750°C temperatures. Elevated temperatures resulted in a higher shear capacity loss in the beams with a lower tension reinforcement. Stiffness of the beams reduced, whereas midspan deflection corresponding to ultimate load increased after elevated temperatures. Load-shear crack width responses indicated a brittle failure in the beams up to a temperature of 350°C. Ductile failure was perceived in the specimens tested after 550 and 750°C. The strains in tension reinforcement corresponding to ultimate load decrease as the exposure temperature increases. Theoretical predictions provided reasonable estimates of shear capacities up to a temperature of 350°C; in contrast, shear capacities of beams exposed to over 550°C were found up to 46% higher. The experimental results were used to develop an equation for the computation of the shear capacity of RCSB after exposure to elevated temperatures. [ABSTRACT FROM AUTHOR]

Due to the bridging effect of steel fibers in ultra-highperformance concrete (UHPC), reinforced UHPC beams exhibit much higher post-cracking stiffness and smaller deflection compared with conventional reinforced concrete beams. This paper attempts to develop a mechanics-based yet simplified method for determining the instantaneous deflection of reinforced UHPC beams at serviceability limit state. First, a validated numerical procedure is developed to predict the moment-curvature behavior of reinforced UHPC sections under serviceability conditions. Then, the tension stiffening in the beam is evaluated. It is found that the moment-curvature response of the UHPC section at the stabilized microcracking stage is almost parallel to that of the fully cracked section, with a nearly full tension-stiffening response. On this basis, a design equation for the effective moment of inertia is derived for calculating the deflection of reinforced UHPC beams. It is found that the proposed approach can provide reasonably conservative deflection predictions, with a mean value of the predicted-tomeasured deflection ratio of 1.21 and a standard deviation of 0.309, by comparing its predictions with available experimental results of 82 flexural tests. [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]

Several approaches were used to explore the characteristics of reinforced concrete (RC) structural elements. Experimental work in the lab was extensively used as a means to examine the structural response and influence of different parameters under shear loads. Also, using numerical analysis to look into these components has been proven effective. This paper focuses on the shear conduct and response of circular beams reinforced with steel bars using the finite element (FE) model by considering the effect of reinforcement type and ratio, shear span-depth ratio (a/d), and member’s size. The FE model results were confirmed with the experimental outcomes of full-scale circular RC specimens tested earlier by scientists. The outcomes from the numerical study displayed that the proposed finite element replica was capable of simulating the characteristics of the beams, tested experimentally in the lab, with credible accuracy. From the FE model, it was found that the concrete shear contribution is best described as a formula that is inversely proportional to the member’s depth and directly proportional to the square root of axial stiffness of the reinforcement. [ABSTRACT FROM AUTHOR]

In this study, a first attempt is established to develop a rational yet simplified truss analogy approach to predict the full response of reinforced concrete deep beams. The bilinear load-deflection curve is characterized by two key points—namely, yielding and ultimate. Timoshenko’s first-order shear deformation theory is invoked to linearize the strain profile by including the shear strain contribution. Based on the levels of strain in different truss members, a nonlinear analysis scheme is devised to compute the yielding and ultimate load and displacement. Comparisons with a wide range of shear span-depth ratios in tested beams are successfully made. Predictions of the response and failure modes are found to agree with experimental observations. [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]

A new composite coupling beam having steel plates that provide active confining pressure of approximately 0.05Asafc' on each side of the reinforced concrete (RC) beam with an orthogonal reinforcement layout is proposed in this research. A weak (unconfined) portion was intentionally left by cutting off the steel plates at 1 in. (25 mm) distance away from the beam ends to absorb the majority of the inelastic deformation. Three coupling beam specimens with ln/h of either 1.5 or 2.5 were tested under lateral displacement reversals to evaluate the cyclic behaviors of the proposed coupling beams. Test results indicated that the use of steel plate confinement significantly enhanced the strength and deformation capacity of RC coupling beam specimens with orthogonal reinforcement layouts. The peak strength of the proposed coupling beams, Vpeak, can be adequately estimated by VMn, the shear corresponding to the development of the nominal flexural strength. The drift capacity of the proposed coupling beams exceeded 8.0%, which was 50% larger than that of specimens using diagonal reinforcement in compliance with ACI 318-19. [ABSTRACT FROM AUTHOR]

The efficiency of ACI 318 and AASHTO strut-and-tie models for designing the reinforced concrete deep beams without web reinforcement is discussed. A database of 232 tests on reinforced concrete (RC) deep beams without web reinforcement was chosen for the investigation. Based on a review of the experimental database, the depth of flexural compression derived using linear elastic analysis appears to be an acceptable approximation for deep beams. Compared to AASHTO and ACI 318-19, ACI 318-14 suggests a higher strut efficiency factor of 0.51 for struts without web reinforcement. When the shear strength limit of ACI 318-14 is considered, the shear strength is estimated with a mean strength ratio of 0.69 and a 4% overestimation. To reduce the overprediction, ACI 318-19 reduces the strut efficiency factor to 0.34 from 0.51, which also decreases the mean strength ratio to 0.51 and eliminates the overprediction of capacity. AASHTO's strut efficiency of 0.45 exhibits a 5% strut efficiency factor estimated from the database. Analysis of the experimental database reveals that the strut efficiency factor decreases with an increase in concrete strength. The lowest strut efficiency by ACI 318-19 may result in an unsafe estimation for high concrete strength. As a result, the strut efficiency factor as a linear function of concrete strength has been presented, which predicts a deep beam capacity with high accuracy--less than 3% overestimation. This study also examines the factors affecting the diagonal cracking load. The beam depth affects the diagonal cracking load, which was ignored in AASHTO. The improved AASHTO formula, accounting for the size effect, predicts diagonal cracking load with the same accuracy as AASHTO's original expression while reducing overestimation to 5% from 13%. [ABSTRACT FROM AUTHOR]