Enhancement Of Shear Capacity Research Articles

Study on the Shear Performance of the Interface between Post-Cast Epoxy Resin Concrete and Ordinary Concrete

The interface of fresh-aged concrete represents a critical vulnerability within monolithic assembled monolithic concrete structures. In this paper, the shear performance of the interface between post-cast epoxy resin concrete and standard concrete is studied using experimental methods and finite element analysis. The objective is to furnish empirical data that support the broader adoption of epoxy resin concrete in assembled structures. A direct shear experiment of 19 Z-shaped samples and a computation of 20 finite element models were completed. The results from both experimental and computational analyses provided insights into several factors influencing the shear performance at the interface. These factors include the pre-cast part of concrete strength, the friction coefficient of the interface, the longitudinal reinforcement ratio at the interface, the compressive strength of concrete in the post-cast part, and confining stress. The findings indicate that utilizing epoxy resin concrete for post-cast material, roughing the interface, and setting keyways can enhance the shear performance of the interface so that it equals or even exceeds the cast-in situ sample. Optimal shear results are obtained when the compressive strength of the post-cast epoxy resin concrete closely matches that of the pre-cast conventional cement. Moreover, increasing the depth of the keyways rather than their width is more effective in improving the shear capacity of the sample. It is recommended that the depth of the keyway should be at least 30 mm, and its width should be no less than three times the depth. As the longitudinal reinforcement ratio at the interface increases, there is an enhancement in shear capacity coupled with a reduction in deformative performance. It is advisable to maintain this ratio below 1.0% to balance the strength and ductility effectively.

Shear performance and strength of reinforced concrete non-prismatic beams with basalt fiber reinforced polymer rebars

Tapered beams, which are horizontal structural elements, possess varying moments of inertia across their length. Among these, the pier cap mode is widely employed in engineering applications. This research explores the influence of incorporating basalt fiber reinforced polymer (BFRP) bars on the shear strength of eight concrete haunched beams. While two of these beams were straight beams, the others have different inclination angles. The study aimed to examine two main factors: the angles of tapered part in the compression chord and the effect of BFRP stirrups. Results from the experiment revealed a direct correlation between increasing tapered angles and the enhancement of shear capacity in haunched beams. Consequently, a comprehensive analysis was conducted using three different codes, leading to the formulation of proposed equations derived from semi-empirical methods. The analysis demonstrated a high level of accuracy in predicting shear strength with a satisfactory safety margin.

Shear capacity of miniature beams with continuous staggered spiral stirrups

Scaled-down-reinforced concrete beams with rectangular staggered continuous spiral stirrups are experimentally investigated. Scale-down RC beams were considered in the current research due to ease of construction and economic feasibility. As the brittle shear failure should be avoided, continuous research trials have been conducted to find an effective technique to improve shear failure mechanism. Twenty-two beams were investigated for shear behavior under 4-point static push-over load considering the normal stirrups and compared with continuous staggered spiral ones. Stirrup spacing, shear arm ratio a/d, and shear reinforcement configurations are the main variables. All beams were designed and scaled down to be one-eighth of the full-scale beams. To minimize the size effect of using small-scale models, mortar was used instead of conventional concrete. The focus in this study was related to improved shear capacity, dissipated energy, and shear cracks propagation. It was found that using spiral reinforcement instead of normal one leads to a significant enhancement in shear capacity and dissipated energy by 33% and 45%, respectively. Therefore, the prototype RC model expected capacities were detailed calculated considering the scale-down factor used by authors. The experimental results were compared by calculated values according to international standard and specifications.

Overcoming the brittleness of shear failure: A new FRP-RSC strengthening philosophy

Due to the linear elastic stress–strain behavior of carbon fiber reinforced polymer (CFRP), the ductility of CFRP shear-strengthened reinforced concrete (RC) beams will be significantly reduced. Compared with shear capacity enhancement, increasing the ductility of CFRP shear-strengthened RC members is a much more challenging task, and a satisfactory solution has yet to be found. This paper introduces a new methodology that combines the brittle fiber reinforced polymer (FRP) with ductile rubber support composite (RSC) to form the FRP-RSC strengthening system. The variable stiffness RSC can adjust the stiffness of the strengthening system, which is achieved by the changed shear transfer actions in FRP, transverse reinforcement and concrete. Eight specimens were tested to evaluate the effectiveness of the FRP-RSC strengthening method. Experimental tests demonstrated that the displacement ductility with this FRP-RSC technique was 2.15 times that of the conventional externally bonded (EB) FRP strengthening, reaching remarkably 5.24. The mechanisms for enhancements in ductility, deformability and shear capacity were revealed. Poor matches were observed between the predicted FRP shear strength contribution (Vf) per existing models and test data. A new model that can predict Vf of FRP-RSC strengthened RC beams was developed, and better agreements between predictions and experimental results were obtained.

Post-buckling shear capacity of steel plates with opening strengthened by fiber fabric

Shear capacity is one of the most important factors of steel plates and the steel plates with opening is widely adopted in engineering. This study investigates steel plates reinforced with fiber fabric. Opening shapes, positions, panel thicknesses, and material strengths, are considered to assess the effectiveness of fiber fabric in reinforcing steel plates. Two types of fibers, carbon fiber and basalt fiber, are employed. Specimens with various opening positions and shapes are meticulously designed. The study includes an analysis of how effectively fiber fabric improves shear capacity and examines the resulting failure modes. A comparison is made regarding the shear behavior of plates reinforced with different types of fiber fabrics. The study also explores how plate thickness influences the strengthening effect. The results indicate that the presence of fiber fabric does not enhance the shear capacity of steel plates without openings. Carbon fiber demonstrates a greater enhancement in shear capacity compared to basalt fiber. The use of fiber fabric and epoxy resin to reinforce thin steel plates shows limited improvement in shear capacity. A numerical model is proposed to simulate plates reinforced with fiber fabric, incorporating a nonlinear spring element to represent the behavior of epoxy resin.

Shear capacity investigation of RC concrete beams using self-prestressing Fe-based shape memory alloys strips

Shear failure is a sudden and brittle failure, which causes human and economic losses. Hence, enhancement of shear capacity is critical for shear-deficient members of existing structures. In this study, the effectiveness of using Shape Memory Alloy ‘SMA’ strips on the shear capacity of reinforced concrete (RC) beams was investigated in a series of experiments. The experimental work included the study of six RC beams with a 200 × 300 mm cross-section considering shear parameters such as transverse shear reinforcement and the effect of prestressing. Beams were strengthened in U configuration using Fe-SMA strips 30 mm wide and anchored by one expansion anchor (M10-Hilti). The testing was performed in a simply supported condition where each beam was tested twice. The purpose of testing specimens twice was to confirm the results. The activation of the strips was achieved by heating the strips using a custom-made heater up to 200°. The method was proven effective, with an increase in shear capacity of up to 32–45% and 24–25% for specimens strengthened with passive strengthening (non-activated strips) and specimens strengthened by activated SMA strips, respectively. However, the active strengthening improved serviceability conditions by delaying the appearance of cracks and reducing the crack width. The occurrence of the main crack was delayed by 12.5–19.2%, the width of the crack was reduced by more than 65% compared to the reference beam, and the angle of the main crack increased compared to the reference beam as a result of activation. Beams containing internal transverse reinforcement performed better than the beams without shear reinforcement.

Shear behavior of two-span continuous concrete deep beams reinforced with GFRP bars

To investigate the shear behavior of reinforced concrete (RC) continuous deep beams with glass fiber reinforced polymer (GFRP) bars, four large-scale beams with a constant shear span-to-overall depth ratio of 1.2 and different GFRP shear reinforcement ratios were tested. Digital image correlation technology was used to track the kinematics of diagonal shear cracks in the shear span. It was found that the moment redistribution in the deep beams was very limited. A tie-arch action was confirmed in the tested deep beams with the crack propagation and the strains developed in longitudinal reinforcements. For the beams without GFRP stirrups, the aggregate interlock contribution constituted 46.3% of the total shear resistance. For the beams with GFRP stirrups, however, the shear contribution of aggregate interlock was less significant. As the GFRP shear reinforcement ratio increased from 0% to 0.47%, the failure mode changed from shear compression failure to compression strut failure. As the shear GFRP reinforcement ratio increased from 0.24% to 0.32% and 0.47%, the load-carrying capacity increased by 35.5% and 73.5%, respectively. The minimum required GFRP shear reinforcement in ACI 440.1R-15 was ineffective for the tested GFRP-RC continuous deep beams in terms of shear capacity enhancement and shear crack control. Finally, a database of shear tests on continuous GFRP-RC beams was collected to assess the ability of strut-and-tie methods in three code guidelines.

External shear strengthening of RC beams with basalt fiber sheets: An experimental study

Basalt fiber is an eco-friendly fiber and a promising material for the strengthening of reinforced concrete (RC) structures due to its various advantages such as low cost, better resistance to chemical attack, good thermal characteristics and higher tensile strength than the E-glass fiber. However, only a few experimental investigations have been reported in the literature on the strengthening of RC beams with basalt fiber reinforced polymer (BFRP) composites. Therefore, the current study targets to investigate the efficacy of basalt fiber sheets as a shear strengthening material for RC beams. Ten RC beams were examined under the four-point loading system. The influence of different parameters such as width, orientation and amount of the BFRP strips, type of strengthening schemes, type of fiber sheets (glass and basalt) and the effect of the level of pre-loading were investigated in the present study. The experimental outcomes have shown that the failure load of strengthened beams increased by 17–50%, whereas the toughness enhanced up to 2.74 times in comparison to the reference specimen. In addition, it has been noticed from the current investigation that the overall effectiveness of basalt fiber sheets in increasing the shear capacity is 20% higher than that of the glass fiber sheets and the enhancement in shear capacity decreases with an increase in preload level.

Combined effects of Carbon Fiber Reinforced Polymer flexural reinforcements and post installed shear dowels on the performance of flat slabs

The sudden punching shear failure of flat slabs is a critical issue. The combined effects of externally strengthened Carbon Fiber Reinforced Polymer (CFRP) flexural reinforcements and post-installed CFRP shear reinforcements which explain the real behavior in the strengthening phase of a shear deficient slab, on the punching shear performance are not fully explained. In this study, the flat slab panels of 1200 mm × 1200 mm × 100 mm were retrofitted with seven alternative bonding arrangements of CFRP to investigate the combined effects of shear dowels and flexural reinforcements. A transient load was applied using a stub column, size 100 mm × 100 mm located at the center of the slab. The non-strengthened specimens failed in punching shear. The strengthened specimens showed a maximum punching shear capacity enhancement of 120%. A numerical model was also developed to identify the load transfer behavior of post-installed CFRP shear dowels. Further, the effects from the end anchorage of external CFRP and the refilling material at drilled locations to install CFRP shear strengthening scheme were also determined.

Strengthening of shear deficient RC deep beams using GFRP sheets and mechanical anchors

This paper presents the test results of an experimental study on shear deficient reinforced concrete (RC) deep beams strengthened with externally bonded glass fibre reinforced polymer (GFRP) sheets and mechanical anchors. A total of nine deep beams are prepared. One beam is kept as un-strengthened. Four beams are strengthened using GFRP sheets only at shear spans by varying the number of layers. The remaining four beams are strengthened using both GFRP sheets and mechanical anchors at shear spans. The shear capacity, failure mode, and deflections are studied with respect to the different strengthening techniques. The optimum enhancement in shear capacity of these beams is observed as 25.64% and 55.5% for GFRP strengthened beams and GFRP strengthened anchored beams, respectively with respect to the un-strengthened beam. Moreover, the experimental results are also compared with the results predicted from the design guidelines and models available in the literature, which shows good agreement.

Constitutive models for nonlinear analysis of SFRC corbels

In this paper, nonlinear constitutive models are proposed for steel fiber reinforced concrete (SFRC) in compression and tension. The models were implemented in the finite element computer program ANSYS for 3-D nonlinear analysis of SFRC corbels under monotonic static loading. Several validation studies have been performed for normal-strength and high-strength SFRC corbels with constant or variable depth. Good agreement is generally achieved between experimental and numerical results for the load-deflection curves and crack patterns. Additionally, parametric studies have been performed in order to investigate the effect of structural parameters on the performance of SFRC corbels. It was found that: (1) increasing the concrete compressive strength (fc’) improves corbel shear capacity and toughness, (2) the inclusion of steel fiber (Vf) delays premature shear failure for corbels and enhances strain ductility, (3) an enhancement in shear capacity and strain ductility is noticed by increasing the ratio of horizontal stirrups (ρh), and finally, (4) increasing the shear span-to-depth ratio (a/d) reduces the shear capacity of SFRC corbels. Corbel shear capacity increases by 27% due to a 33% increase in (fc’), by 31% due to Vf = 1% inclusion, by 20% due to a 1% increase in (ρh), and by 20% due to a 39% decrease in (a/d) ratio. The proposed nonlinear finite element approach is efficient in determining the expected enhancement in shear capacity and ductility of SFRC corbels, and consequently in optimizing design parameters for such elements.

Experimental study on the effect of swimmer bars as shear capacity enhancement in footing

Experimental study on the effect of swimmer bars as shear capacity enhancement in footing

Mechanical behavior of concrete beams shear strengthened with textile reinforced geopolymer mortar

This paper presents results from static load tests on ten RC beams, including eight shear strengthened beams with textile reinforced geopolymer mortar (TRGM), one shear strengthened beam with textile and epoxy resin, and one un-strengthened beam. The effects of number of textile layers, textile geometry, adhesive type and anchorage measures using steel strips on shear capacity of strengthened beams were investigated. The effective strain of textile in TRGM strengthened beams at failure were compared to that in shear strengthened beams with ordinary textile reinforced mortar (TRM) in previous studies. The data from tests show that the enhancement of shear capacity achieved by one layer and two layers of TRGM strengthening with respect to the un-strengthened beam are 47% and 106% respectively. And the shear capacity can get further enhancement by 15–21% when steel strips anchorage is incorporated. The effective strain developed in textile of TRGM shear strengthened beams is comparable to or even higher than that in TRM strengthened beam with similar wrapping configuration. Although one layer of TRGM is about half as effective as its resin-based counterpart in terms of increasing shear capacity, TRGM is a very promising solution for retrofitting and strengthening RC members, due to its superior fire resistance, excellent corrosion resistance and good weatherability. The calculated shear capacity of TRGM strengthened beams, using the modified model for the effective strain for TRGM, shows a reasonable agreement with the tested results.

Hybrid NSE/EB technique for shear strengthening of reinforced concrete beams using FRCM: Experimental study

The externally bonded (EB) fabric reinforced cementitious matrix (FRCM) has successfully been used as a structural strengthening for various applications including flexural and shear strengthening of reinforced concrete (RC) beams, flexural strengthening of RC slabs and column confinement. However, the EB-FRCM system is characterized by poor FRCM/concrete bond leading to premature debonding of FRCM off the concrete substrate, particularly for thicker FRCM. The present paper reports on an experimental study on the efficacy of a pioneer form of hybrid near surface embedded and externally bonded technique using FRCM composites (NSEEB-FRCM) for shear strengthening of RC beams. With such a technique, higher thickness of FRCM composites can be applied with less likelihood of debonding that is normally experienced when using the EB-FRCM system. Thirteen shear-deficient medium-scale RC beams were constructed, strengthened in shear and tested under three-point bending test. The test parameters were: (a) FRCM type (polyparaphenylene benzobisoxazole, carbon, and glass), (b) strengthening configuration (full versus intermittent strips), and (c) number of fabric layers.The percentage enhancement in the shear capacity of the beams ranged from 43% to 114% indicating the successful implementation of the strengthening methods provided. An average enhancement in shear capacity of 83%, 72% and 62% were observed in carbon FRCM, glass FRCM and PBO-FRCM, respectively. The failure mode of the strengthened specimens was sensitive to the type and configuration of FRCM in addition to the number of FRCM layers. The strengthening systems also resulted in higher deflection at failure and energy absorption value of the strengthened beams with an average of 94% and 204% relative to the reference specimen, respectively.

Assessment of shear capacity methods of steel fiber reinforced concrete beams using full scale prestressed bridge beams

Steel fiber addition in concrete is widely known to increase the non-flexural performance of concrete structures such as shear capacity. Design guides such as fib Model Code (2010) have recognised this effect and that these guidelines may become widely accepted. The current design guides are based on laboratory scale tests which may be compromised by the scale effects. This paper reports the results of full sized precast prestressed bridge beams that were fabricated and tested to shear failure. Two beams had steel fiber and two beams were plain concrete. None of the beams had any vertical shear reinforcements. The addition of steel fiber at the dosage of 60 kg per cubic metre resulted in more than twice the shear capacity as compared to the beams without steel fibers. The results of the fiber reinforced beams were compared with the calculated shear capacity of the fib Model Code (2010) and plastic design method. This paper presents a method to include prestress in previously developed plastic design method. The model code method predicted an increase of shear capacity of 22 % as compared to the experimental results of 112 % increase due to steel fiber addition. This demonstrates that the model code is not effective in taking into consideration of the contributions by steel fibers. The plastic design approach predicted an increase of shear capacity of 122 % which is close to the experimental values. Based on this full scale tests, the plastic design approach appears to be more suitable for estimation of shear capacity enhancement when steel fibers are used.

Finite Element Analysis of Steel Fiber Reinforced Concrete (SFRC): Validation of Experimental Shear Capacities of Beams

Finite element models are analyzed and validated with the experimental shear capacities of steel fiber reinforced concrete (SFRC) as well as plain concretes. In this work, steel fibers with low aspect ratio which are commonly available in Bangladesh are used and sufficient capacity enhancements are attained. Two different aggregate types are used to make the SFRC and plain concrete beam specimens, i.e. stone and brick, and also modelled in the finite element (FE) platform of ANSYS 10.0 with SOLID65 element. The experimental plan intended to investigate the shear capacity enhancement of three different types of beam specimens, i.e. single shear, double shear and flexural shear. All the specimens are tested in the 1000kN capacity digital universal testing machine (UTM) and the strain data are obtained from digital image correlation technique (DICT) using high definition (HD) images and high speed video clips. Test results showed the increase in shear capacity of about 30% to 170% of beams made of SFRC with an indication of increase in ductility. FE models are analyzed extensively and validated with the experimental stress-strain behaviours by optimizing the Poisson's ratio, modulus of elasticity, tensile capacity and stress-strain behaviours. FE models showed the same structural response and failure modes as found in experimental investigation. This paper can contribute to the construction industry of Bangladesh about SFRC with reliable experimental data and FE analyses.

Experimental Study on Shear Capacity of Prestressed SFRC Beams

In order to study the shear capacity enhancement effect of prestressed technology to steel fiber reinforced concrete, the practical formulas were proposed for evaluating the shear-strength of unbonded prestressed steel-fiber reinforced concrete beams (UPSFRCB) through the test and study of shear capacity of UPSFRCB with simply supported ends. Various factors affecting the shear strength of UPSFRCB, such as steel fiber, prestress and shear-span to depth ratio were analyzed. The result is of importance to the popularization and application of prestressed steel-fiber reinforced concrete.

Comparison of shear behavior of masonry walls with and without reinforcement

The aim of the paper is to present the influence of different reinforcement directions (horizontal, vertical and the combination of the two) on the shear resistance, failure modes and crack pattern of solid masonry walls. In order to investigate the effect of vertical reinforcement a new type of bonding of bricks was developed. The favorable influence of mixed reinforcement is clearly shown. The crack pattern modification effect and the shear capacity enhancement of reinforcement are unambiguously proved. Force-displacement diagrams, extreme horizontal loads applied and maximum displacements at the top are compared and evaluated for all specimens.

Upgrading of ductility and shear capacity of reinforced concrete beams of highway bridge bents

Two techniques to upgrade the ductility and shear capacity of reinforced concrete beams of existing highway bridge bents were examined. An experimental program that consisted of 3 scaled models was conducted. The specimens were tested using statically reversed cyclic loading. The first specimen was a control specimen. The beams of the other 2 specimens were upgraded. External steel plates were bonded to the beam in the first upgrading technique and external steel rods were employed in the second upgrading technique. The characteristic behavior of each specimen was experimentally clarified in terms of hysteretic behavior, displacement response ratio, maximum displacement, damage propagation, energy dissipation, equivalent damping factor, and final failure mode. The study revealed that the 2 upgrading techniques could result in enhancement of the overall behavior of the bridge bents. Upgrading the beams utilizing external steel rods, however, was shown to be more effective in resisting future earthquakes. Analytical modeling of the highway frames utilizing FEM was performed. The numerical simulation resulted in a satisfactory accuracy of the predicted behavior. A calibrated baseline FE model was derived and could be employed to quantitatively identify the strengthening effect on resulting behavior of the bridge bents. The study provides an addition to the experimental data for ductility and shear capacity enhancement of bridge bents, and may assist selecting the most appropriate upgrading technique.

와이어로프로 외부 보강된 철근콘크리트 연속 T형 보의 전단내력

A simple unbonded-type shear strengthening technique for reinforced concrete beams using wire rope units is developed. Six two-span continuous T-beams externally strengthened with wire rope units and an unstrengthened control beam were tested. The main variables investigated were the amount and prestressing force of wire rope units. All specimens had the same geometrical dimension and arrangement of internal reinforcement. Influence of the distribution of vertical stresses in beam web owing to the prestressing force of wire rope units on the diagonal shear cracking load and the ultimate shear capacity of beams tested is presented. Based on the current study, it can be concluded that the amount and initial prestress of wire rope should be limited to be above 2.5 times the minimum shear reinforcement ratio specified in ACI 318-05 and below 0.6 times its own tensile strength, respectively, to ensure the enhancement of shear capacity and ductile failure mode of the strengthened beams. A numerical analysis based on the upper-bound theorem is developed to assess the shear capacity of continuous T-beams strengthened with wire rope units. From the comparisons of measured and predicted shear capacities, a better agreement is achieved in the proposed numerical analysis than in empirical equations recommended by ACI 318-05.