Shear Behavior Of Deep Beams Research Articles

Shear behaviour of deep beams strengthened with high-strength fiber reinforced concrete jackets

The study addresses the pressing need for effective strengthening of reinforced concrete (RC) members, specifically focusing on shear-critical deep beams. One of the most effective methods for strengthening RC members is the fiber reinforced concrete (FRC) jackets. However, limited number of studies have been conducted on deep beams strengthened with FRC. To address this gap, this paper presents an experimental investigation for strengthening of shear-critical deep beams using high-strength fiber reinforced concrete (HFRC) jackets. The experimental program involves testing three large-scale deep beams, including a reference specimen and two strengthened beams with thin HFRC jackets of different thicknesses (34 mm and 26 mm). The HFRC jackets featured straight steel fibers with a volumetric ratio of 1.13 %. According to the experimental results and analysis, it is found that an HFRC jacket of 34 mm thickness upgraded the strength by around 25 % and enhanced the crack control by reducing crack widths by around 50 % at the same absolute load with respect to the reference specimen. From the measured deformed shapes of the compression zone of the specimens, it is concluded that the main principles of the two-parameter kinematic theory of deep beams remain valid for HFRC-strengthened members, and these principles can be used to establish a complete modelling approach for such members.

The nonlinear analysis of reactive powder concrete effectiveness in shear for reinforced concrete deep beams

Abstract The aim of this article is to investigate the effect of using reactive powder concrete (RPC) for reinforcement concrete deep beams (CDBs) to study the shear effect by the numerical analysis. The method of finite element analysis model simulations using a program was used. The characteristics of RPC and the deep beam of reinforced concrete were obtained from previous scientific research. Non-linear analysis for two models of deep beams, one with RPC and the other without using it, was conducted to compare with experimental results from recent tests of deep concrete beams with RPC and loaded until failure. The data obtained from the specimens have many factors related to the effect of the strength and action of reinforcement CDBs such as shear load deflection, crack pattern, mode failure, and concrete strength. On the other hand, the mesh changing was investigated in terms of the maximum concrete strength and the running time by changing the mesh size to 50, 25, and 15. Models were simulated with a two-point load using a shear span-to-depth with an av/d ratio of 0.77. The difference in percentage deflection between the numerical and experimental models’ data was observed at 2.60 and 5.9% for concrete deep beam and RPC deep beam, respectively, and the maximum shear load was 2.27 and 5.40%. The importance of the outputs of this article lies in bridging the research gap of this new topic and identifying the shear behavior of deep beams reinforced with RPC due to the lack of research related to this topic. It was noted that the obtained data for finite element analysis are very consistent with the previous laboratory scientific research, while the error rate did not exceed 10%.

Experimental study on the effects of external strengthening and elevated temperature on the shear behavior of ultra-high-performance fiber-reinforced concrete deep beams

The shear behavior of deep beams, especially of ultra-high-performance fiber-reinforced concrete (UHPFC), is rather intricate, as it depends on several factors, including its depth, concrete strength, amount of flexural and shear reinforcements, the ratio of shear span to depth, and the bearing area under the load and at the support. Moreover, these beams may be exposed to elevated temperatures requiring strengthening, which has not been adequately studied. This study examines experimentally the shear capacity of UHPFC deep beams strengthened using carbon fiber-reinforced polymer (CFRP) sheets for improving the shear strength of deep beams after exposure to an elevated temperature. Eight specimens were cast in four groups of two specimens each. Testing of the beams of the first group was performed at the ambient temperature, whereas the beams of the second group were tested after being exposed to a temperature of 450 °C. For the third group, the deep beams were strengthened by CFRP U-wrap strips and tested at the ambient temperature, whereas the beams of the fourth group were subjected to the elevated temperature of 450 °C, followed by strengthening using CFRP U-wraps and then testing to collapse. The test results indicated that the post-peak behavior was affected significantly by the elevated temperature. Moreover, the experimental results indicated the excellent performance of strengthening schemes in improving the post-cracking behavior of UHPFC deep beams, enhancing shear strength (up to 16 %), energy-based ductility index (39 % to 648 %), and deflection ductility index (68 % to 144 %). An analytical model is developed to predict the load-carrying capacity of UHPFC deep beams strengthened after exposure to elevated temperature.

Investigation on shear behavior of reinforced concrete deep beams without shear reinforcement strengthened with fiber reinforced polymers

Shear failure is an undesirable type of failure in terms of structural safety. Particularly, reinforced concrete (RC) deep beams without shear reinforcement are vulnurable to shear failure. In order to improve the shear behavior of such beams, externally bonded (EB) fiber reinforced polymer (FRP) as a strengthening technique is being applied to the outer part of the beams. However, investigations on the shear behavior of deep beams without shear reinforcement strengthened with FRP materials are insufficient in the literature. Therefore, a comprehensive experimental study was carried out on RC deep beams without shear reinforcements strengthened with fully wrapped FRP strips. The experimental parameters were chosen as the shear span-to-effective depth ratio (av/d), the number of carbon layers, the span length between carbon strips, and the type of FRP. A total of sixteen deep beams, four of which were reference beams, were fabricated and tested under three point bending load until failure. According to the experimental results, the gain percentage both in the shear and deflection capacities of strengthened deep beams increased with the av/d. Additionally, the failure modes and crack patterns of strengthened deep beams were different from those of the reference beams. Moreover, all test parameters affected the ductility behavior of deep beams having av/d of 1.5 and 2 positively. A comparative study was also conducted employing the methods commonly used in the literature and the methods based on the strut and tie model. It was observed that the methods based on strut and tie model provided superior estimates over the models commonly used in the literature.

Experimental study on shear behavior of reinforced concrete deep beams with high-strength bars under uniform load

This study aimed to investigate the shear capacity performance for five deep beams with reinforced high strength concrete under uniform load to enable a better understanding of the effects of longitudinal reinforcement ratio and vertical stirrup ratio. The shear behavior test was completed by simulating uniform loading with eight points of concentrated loading. The dimension of five test specimens is 1600 mm × 200 mm × 600 mm. The longitudinal reinforcement ratio is set to 0.67%, 1.05%, 1.27%, and the vertical stirrup ratio is taken to be 0.25%, 0.33%, 0.5%. Through measuring the strain of steel bar, the strain of concrete, and the deflection of mid-span, the characteristics of the full process of shear capacity, the failure mode and the load–deflection deformation curve were examined. Based on this test, a 3D finite element model is established to verify the reliability of the test results. In addition, the calculation formula in the Code for Design of Concrete Structures (GB50010-2010) is used to calculate the shear behavior of deep beams, and the finite element calculation results and the code calculation results are compared with the test values. The results show that three typical failures mainly occur in deep concrete beams under uniform load: diagonal-compression failure, splitting failure, and local-compression failure. With the increase of longitudinal reinforcement ratio, the ultimate bearing capacity gradually increases. The increase of vertical stirrup ratio is helpful to improve the shear behavior of deep beams and inhibit the development of diagonal cracks. The 3D finite element model calculation results are close to the experimental values, and the finite element model can reasonably reflect the stress mechanism of deep beam members. Finally, the average value of ultimate bearing capacity of the experimental values compared with the code (GB50010-2010) calculation results is 2.208, and the results are on the conservative side. The obtained results show the code (GB50010-2010) has sufficient safety reserves.

Modeling the shear behavior of deep beams strengthened with FRP sheets

While external FRP sheets are a viable solution for the strengthening of concrete members, there is a lack of mechanical models that can capture their effect on the shear strength of deep beams. This is in part due to the complex debonding and rupture behavior of FRP, which occurs in parallel with the activation and failure of the other shear mechanisms in deep beams. To address this gap, the current paper proposes a kinematics-based model for the behavior of shear-critical deep beams with externally bonded FRP sheets, including side and U-shape sheets, full wraps and inclined strips. The FRP contribution is modeled as a function of the displacements in the shear cracks by using appropriate constitutive relationships. The model is validated with 20 tests from the literature showing adequate shear strength predictions. Parametric analyses are used to show that the effectiveness of FRP sheets decreases with decreasing shear-span-to-depth ratio and increasing member size. The predictions of the ACI and CNR design equations are also evaluated with the help of the proposed model. While design codes do not account for initial cracks at the time of strengthening, the kinematics-based model is used to simulate this effect by later activation of the FRP.

Impact of reinforcement and geometry of deep beam – Research perspective

Present construction industry is moving towards high rise and multi-storeyed building which requires the deep beam element to dissipate the load to adjacent element. Loads are transferred from slab to column by beams, and in the case of longer spans, deep beams are used. In deep beams, the theory of simple bending principles does not apply and does not follow the conventional beam theory, and is designed in accordance with non-linear stress distribution in depth of the structural member. A complete literature review focusing on shear strength of deep beams was conducted. Design criteria such as web reinforcement, shear length to depth ratio, vertical reinforcement, beam size, beam depth, side face reinforcement, percentage of reinforcement, crack width criteria, and shear span deflection is varied by the researchers to analyze the shear behaviour of deep beams. Since shear failure is a key concern, of deep beam, many researchers have researched the shear strength behaviour of deep beams in the previous years. Possibility to shear failure is high in deep beam, so structural reinforcements must be revamped as soon as possible. Web gaps in deep concrete beams interrupt the transfer of loads to the supports, reducing the member's shear strength. While such gaps can have a substantial impact on the structure's life, most study on deep beams has concentrated on the shear behaviour of concrete members. Present research lays the groundwork for presenting a new shear strengthening technique during member design.

Experimental investigation of dimensional ratio effects on shear capacity of high-performance cementitious composites deep beams

Deep beams are generally used as main load-bearing beams or pile caps which are very common in high rise buildings. The span to height ratio of beams is an essential parameter in their flexural and shear behaviors . The usage of composite concretes conjuncture with fibers enhances the deep beams to overcome the relative brittleness and fragility of concrete and its low energy absorption. In this paper, the experimental research on eight deep reinforced concrete beams cast and replaced with high-performance cementitious composites was carried out. Two group specimens with 2% steel fiber and without fiber, the same height, and similar reinforcement details, and also different span to height ratios from 0.75 to 2 were considered and tested with the three-point flexural method. The experimental ultimate shear strength was compared with the predicted value in different codes. The test results indicated that the load-bearing capacity of deep-beam specimens was increased up to 84.8% with the same dimension when replacing conventional concrete with cementitious composites containing 2% of steel fiber. • New relations suggested to determine the ultimate capacity of deep beams made from cementitious concrete with fiber. • An experimental study was conducted regarding the shear behavior of deep beams using this material, might be a sort of innovation. • Extra work on structural aspects and applying this material and the behavior of deep beams made from this material are of high importance.

Analysis of influencing factors on shear behavior of the reinforced concrete deep beams

A database including 833 specimens on reinforced concrete (RC) deep beams with shear failure is presented in this paper. Comprehensive influences of web reinforcement ratio, shear span-to-depth ratio, depth-to-width ratio, and compressive strength of concrete on the shear behavior of deep beams are discussed. It is found that the normalized shear strength of deep beams decreases with an increase of the shear span-to-depth ratio and this trend is affected significantly by the concrete strength, depth-to-width ratio, and web reinforcement ratio. Besides, the restrictions on minimum web reinforcement and minimum sectional size are investigated. It is found that the restrictions on minimum web reinforcement and the minimum sectional size are significantly affected by the web reinforcement ratio and are closely related to the reinforcement strength and concrete strength. However, the effect of the strength ratio of concrete to shear reinforcements on the limit of the amount of web reinforcements has been ignored in current codes. The characteristic value of web reinforcement, considering the web reinforcement ratio and the strength ratio of concrete to shear reinforcements, is proposed. For the horizontal and vertical reinforcements, the minimum characteristic values of 0.54 and 0.25 are suggested as the restrictions on the minimum amount of web reinforcement, respectively. The maximum characteristic values of 1.5 and 1.7 are proposed as the restriction on the minimum sectional size. Moreover, an equation for the ultimate shear strength of deep beams corresponding to the minimum sectional size is also suggested. Compared with the relevant provisions of the current codes, the suggestions on minimum web reinforcement requirements and minimum sectional restrictions are better.

Effect of partial replacement of coarse aggregate by polystyrene balls on the shear behaviour of deep beams with web openings

Thirteen specimens were experimentally tested under single midspan concentrated loads to study the shear behavior of lightweight concrete (LWC) and normal weight concrete (NWC) deep beams with web openings. In this research, the term LWC refers to the concrete obtained by partially replacing aggregate by polystyrene foam balls not the concrete containing lightweight aggregate. This resulted in a weight reduction of LWC beams in this research by approximately 30% compared to NWC compartments. The studied variables were the dimensions and location of openings, transverse reinforcement ratio, and shear span to depth ratio (a/d). It was found that the overall shear behavior and failure mode for LWC deep beams are comparable to those of the NWC specimens. This is very promising and encouraging to build lighter deep beams of similar structural behaviour as that of NWC deep beams. Dimensions of the openings have a significant effect on the behaviour of failure and shear strength of LWC and NWC deep beams. It was found that increasing the depth of the opening from 20 % to 40 % of the beam depth led to a reduction in the ultimate load by up to 46.4 %. Finite element modelling of the test beams was carried out to verify numerical results versus experimental work and both were very well correlated. In addition, a parametric study was conducted to assess the effect of internal stiffening around openings in deep beams. The maximum enhancement in the shear capacity was approximately 30 % for beams, internally strengthened by additional reinforcement on the perimeter of openings compared to the beams without any reinforcement around the openings. Strut-and-Tie model (STM) was carried out as a rational approach to predict the shear behaviour of studied beams. It was found that STM underestimates the shear of the studied beams compared to experimental results for different tested beams but the agreement between both of them was acceptable. It is recommended that the depth of opening should not exceed 20 % of the depth of the deep beam and if the depth of opening is more than that or lies in the shear span it is highly recommended to strengthen the opening internally by additional reinforcement around its perimeter.

Shear Behavior of Hybrid Fiber Reinforced Concrete Deep Beams.

Hybrid fiber reinforced concrete (HFRC) is based on a multilevel-reinforcement material design that improves both the compressive strength and tensile strength. Investigations of the mechanical performance of HFRC with two types of steel fibers were conducted experimentally. The investigated parameters were the volume fractions of the short steel fibers and long steel fibers. The compressive strength, tensile strength, and flexural strength of the HFRC were researched. The group with volume fractions of 1.5% for the long steel fibers and 0.5% for the short steel fibers exhibited the best flexural strength. The synergetic effect clearly was improved by combining different types of steel fiber. Four HFRC deep beams and one reinforced concrete (RC) deep beam were conducted to consider the shear behavior of these beams. The primary variables included the volume fraction of steel fibers and the web reinforcement ratio. The shear behavior was evaluated based on the cracking pattern, load-deflection behavior, and shear capacity. All of the beams failed due to the formation of diagonal cracks. The results indicated that hybrid fibers contribute greatly to the shear behavior of deep beams. The hybrid fibers led to the formation of multiple diagonal cracks in the deep beams and enhanced the damage tolerance. With the same web reinforcement ratio, the ultimate load and deformation of the HFRC deep beams were better than those of the RC deep beam.

Shear strength modelling of deep beam reinforced with high-strength steel without stirrups

Non-linear finite-element analyses were performed to model the shear behaviour of deep beams with high-strength reinforcement and grade-60 conventional reinforcement, without stirrups. The FE model was compared with experimental results from recent tests of deep concrete beams reinforced with both types of reinforcement and loaded until failure. A detailed comparative study of the FE and experimental results is presented, which demonstrates the capability of the analytical model to describe the observed experimental behaviour. The shear behaviour of beams reinforced with high-strength steel (HSS) was compared with that of beams reinforced with grade-60 steel to demonstrate the benefits of using high-strength reinforcement. The shear design provisions of current codes and mechanics-based models were also compared with the results from the analytical model. The findings of the study showed that diagonal shear cracking strength is independent of the type of reinforcement, while beams reinforced with HSS exhibited higher post-cracking shear strength than beams with conventional reinforcement. Strut-and-tie modelling is recommended for the design of deep beams reinforced with HSS since this method accounts for high strains in reinforcement and accounts for large-size effects. The current code provisions are suitable for slender beams regardless of type of reinforcement.

Experimental investigation of shear models for lightweight aggregate concrete deep beams

The strut-and-tie model has become an effective design methodology for deep beams replacing the conventional beam theory that does not apply to these members due to their geometric or static stress discontinuities. This article examines the applicability of shear models for deep beams with lightweight aggregate concrete. Eight lightweight aggregate concrete deep beams were constructed and tested to failure under concentrated loading. Tests were conducted to investigate the effects of shear span-to-effective depth ratio ( a/d), ranging from 0.26 to 1.04, and an effective span–depth ratio ( le/ h), ranging from 2 to 3, on the failure mode and shear behavior of deep beams. All specimens presented a shear compression or shear-flexure failure mode. Failure from the flexure mode showed a dominant pattern with increasing a/d. The le/ h value minimally influenced the diagonal cracking and ultimate strength of deep beams. In contrast, a/d significantly affected the beam strength. Our results were compared with predictions proposed by American Concrete Institute 318-14, Canadian Standard, EC2, the Tan and Cheng model, the softened strut-and-tie model, and the simplified softened strut-and-tie model, which are all based on the strut-and-tie model. These comparisons indicated that all of these shear methods can be used to predict the shear strength of lightweight aggregate concrete deep beams.

Compression field modelling of fibre reinforced concrete shear critical deep beams: a numerical study

Numerical analyses represent an important way to study the behaviour of both reinforced concrete and fibre reinforced concrete (FRC) structural elements under different loading conditions. Even though advanced computer codes able to model concrete fracture phenomena were developed in the past decades, numerical and analytical tools still require improvements and verifications against new experimental evidences, especially with respects to non-standard or quite critical structures. The present paper focuses on the numerical modelling of the shear behaviour of deep beams whether with fibres (FRC) or no shear reinforcement (PC), by means of a suitable implementation of the modified compression field theory (MCFT) and the disturbed stress field model (DSFM). After a numerical validation against some new available experimental results, specific numerical analyses were performed in order to study the size effect influence on the shear behaviour of FRC elements. These analyses were conducted considering a broad variety of beams, from 250 to 1500 mm high and with different amount of fibres. In the modelling, particular attention was devoted to the nonlinear behaviour of materials, especially with regard to the tension softening of FRC. The latter was modelled through inverse analysis on 3PBTs (EN14651) and by using the recently published Model Code 2010 linear model (MC2010). Refined nonlinear constitutive models and relationships for describing crack spacing and crack width, both in case of PC and FRC, were utilized as well. The numerical results show the reliability of the MCFT and DSFM in modelling both PC and FRC deep beams critical in shear. Moreover, the positive influence of fibres in reducing and significant altering the size effect trend is clearly confirmed by a broad parametric study herein reported.

Five‐spring model for complete shear behaviour of deep beams

AbstractThis paper presents a five‐spring model capable of predicting the complete pre‐ and post‐peak shear behaviour of deep beams. The model stems from a two‐parameter kinematic theory (2PKT) for the shear strength and displacement capacity of deep beams under single curvature. Four of the springs of the model represent the shear resistance mechanisms of the beam, while the fifth spring models the flexural behaviour. The model predicts not only the load‐displacement response, but also the deformation patterns of the beam and how these patterns change with increasing load. Validation studies are performed by using 28 tests from the literature, showing excellent results. The model is used to interpret the tests and to draw conclusions about the behaviour of deep beams. It is shown that shear strength variations of up to 60 % between nominally identical specimens can be caused by variations in the path of the critical shear cracks. It is also demonstrated that loss of bond of large reinforcing bars increases the shear capacity of deep beams. Finally, the five‐spring model is shown to predict the post‐peak shear behaviour effectively, which is important for the analysis of structures under extreme loading.

Shear Strength Prediction of Deep Beams by Softened Truss Model

This paper describes the shear behavior of deep beams. The softened truss model theory, which has been successively used for low rise shear walls and torsion, is extended to deep beams. The theory includes effective transverse compressive stress acting on the shear element and softened concrete stress-strain relationship for the concrete behavior. Theoretical shear strengths were compared with experimental result. Examination of the governing equations helps to identify three major factors that affect the shear strength. They are shear span to depth ratio, transverse reinforcement index and longitudinal reinforcement index. Keywords - Deep Beam, Shear strength, Softened truss model, Reinforced Concrete.

Shear Strengthening of Reinforced Concrete Deep Beams Using Carbon Fiber Reinforced Polymer Laminates

For reinforced concrete beams with the same shear and flexural reinforcements, shear failure is most likely to occur in deep beams rather than in regular beams. Thus, retrofitting of deep beams with shear deficiencies is of great importance. Externally bonded reinforcement such as carbon fiber reinforced polymer (CFRP) provides an excellent solution in these situations. In order to investigate the shear behavior of deep beams with externally bonded CFRP shear reinforcement, 16 deep beams without steel shear reinforcement were cast at the concrete laboratory of New Jersey Institute of Technology. After the beams were kept in the curing room for 28 days, carbon fiber strips and fabrics were applied outside of the beams at various orientations with respect to the axis of the beam. All beams were tested on a 979kN (220kip) MTS testing machine. Results of test demonstrate the feasibility of using externally applied, epoxy-bonded CFRP system to restore or increase the shear capacity of deep beams. The CFRP syst...

고강도 철근콘크리트 깊은 보의 전단거동에 대한 개구부 크기 및 위치의 영향

초록 · 키워드 목차 오류제보하기 등록된 정보가 없습니다. ABSTRACT1. 서론2. 연구방법 및 범위3. 실험결과 및 비교ㆍ분석4. 극한 전단내력 예측모델5. 결론참고문헌요약