Strengthening and design of shear beams

Journal of Advanced Concrete Technology, 2021

The authors have reported from experimental investigation that the use of closed stirrups, U-shaped stirrups and rod-shaped reinforcements as shear reinforcements in reinforced concrete (RC) beams results in clear differences in internal crack patterns and maximum strength. In this study, simulations of the experimental beams were performed using a three-dimensional rigid-body spring model, demonstrating that the behavior observed in the experiments is a mechanical phenomenon that can be reproduced numerically. Using the stress distribution over the beam cross section obtained from the analysis, the beam and arch action components of shear resistance are decoupled and considered from the perspective of the shear resistance mechanism. Further, through analysis of additional cases, the role of the upper and lower horizontal legs of the shear reinforcement, the effect of end anchorages on rod-shaped reinforcements were clarified.

Shear Reinforcement of reinforced concrete members has been great challenge, especially for reinforced concrete beams. The sudden shear failure of reinforced concrete beams due to excessive shear forces made the design for shear reinforcement even more challenging. This type of failure is completely undesirable and it demands higher factor of safety. This pushed researchers to look for other alternatives. Several alternatives to the traditional shear reinforced will be introduced and discussed in this study. New concept of shear reinforced called swimmer bars shear reinforcing system is explored in this study. This new type of swimmer bars require no welding but perform as good as the welded swimmer bars. This study focuses on new and innovative type of swimmer bars. This new swimmer bars system used in this study is called three dimensional space swimmer bars system. This type of swimmer bars are proven to be effective in taking care of the shear forces in reinforced concrete beams. Also, this type of improved swimmer bars system improves on the shear failure mechanism of reinforced concrete beams. Several beams were prepared and tested in the lab. Three different types of beams were prepared; beams reinforced with the new swimmer bars system, beams reinforced with welded swimmer bars system, and beams reinforced with the traditional stirrups. The results of the tests are discussed and presented. The three dimensional space swimmer bars system is basically a reinforcing bar bent several times in the three dimensions forming special configuration along with its coupling swimmer bar. This configuration makes the shear reinforcement system act as plane-crack interceptor rather than linear bar-crack interceptor. This new type of shear reinforcement is proven to be effective and economical. Flexural cracks are monitored throughout the test. The deflection of the beams under gradually increasing load is also measured and presented in this study INTRODUCTION The structural design codes usually emphasize on safety as a first priority that should be taken into consideration when designing steel and concrete structures. The sudden failure mode requires higher factor of safety. The design engineer has to make sure that the mode of failure is acceptable and gives enough warning before failure. The shear failure is not one of the desirable modes of failures and should be avoided. Reinforced concrete beams are one of the common structural elements that carry transversal loads mainly by flexure and shear. The common design approach is to design the beam for flexure then design the beam for shear. The available design codes emphasizes on the ductile flexural failure by reducing the amount of steel reinforcement in the tension area, in order to make sure that the longitudinal tension bars yield first. While the design for shear focuses on providing enough shear resistance exceeding the applied shear force by a margin of safety factor. The shear resistance comes from two different sources; the concrete and the shear reinforcing bars. The concrete shear strength depends on the cross section of the beam, and the concrete compressive strength. Large applied shear force requires shear reinforcing bars of large diameter placed at closer spacing. The design codes provide factor of safety enough to make sure that the beam will survive applied loads during its expected service life. Punching shear in slabs is considered one of the governing factors in the design of flat slabs and raft foundations [1]. Several researchers provided some solution for shear reinforcement including swimmer bars [2]. These swimmer bars added significant shear resistance [3]. Creative pyramid swimmer bars were used [4]. The results were compared with the traditional slab reinforcement. Beams subjected to large shear force exhibit diagonal cracks initiated near the supports. These diagonal cracks have the tendency to widen and propagate moving toward the center of the beam. These cracks are proven to propagate at a faster rate compared with the bending flexural cracks. Steel stirrups, which are shear reinforcing

2012

Embedded Through-Section (ETS) technique is a relatively recent shear strengthening strategy for reinforced concrete (RC) beams, and consists on opening holes across the beam thickness, with the desired inclinations, where bars are introduced and are bonded to the concrete substrate with adhesive materials. To assess the effectiveness of this technique, a comprehensive experimental program composed of 14 RC beams was carried out and the obtained results confirm the feasibility of the ETS method and reveal that: (i) inclined ETS strengthening bars were more effective than vertical ETS bars and the shear capacity of the beams has increased with the decrease of the spacing between bars; (ii) brittle shear failure was converted in ductile flexural failure and (iii) the contribution of the ETS strengthening bars for the beam shear resistance was limited by the concrete crushing or due to the yielding of the longitudinal reinforcement.

Karthick, 2019

Shear failure in concrete structures are very hazardous. These failures can be rarely predicted and happen suddenly. This paper presents the result of experimental investigation that was carried out to examine the shear resistance on longitudinally reinforced concrete beam without shear reinforcements. This experiment involves three series of beam, three of each totally nine numbers of simply supported beams, tested with a two point loading system. The variables of the investigation involve percentage of reinforcing steel and ratio of shear span to effective depth and all other parameters are left constant. The experimental test in this paper indicates the result of mode of failure and ultimate shear strength of a longitudinally reinforced concrete beam. The comparison with conventionally reinforced concrete beams was closest to the experimental results.

Journal of Advanced Concrete Technology, 2021

Various types of shear reinforcement are used for example general closed stirrup and reinforcement bar with mechanical anchor. However, most standards and specifications take only the cross-sectional area of the vertical components of the reinforcement components into account when determining their effect, such as on shear crack development and shear strength. Consequently, the full effect of different shear reinforcement shapes on the shear failure behavior of reinforced concrete (RC) beams is not clear. In this study, differences in shear failure behavior of RC beams using three types of shear reinforcement (closed stirrups, U-shaped stirrups, and rod-shaped reinforcements with mechanical anchor) were investigated by carrying out loading experiments. The three-dimensional displacement distribution on the side faces of each beam and the internal crack patterns were obtained. It was clarified that there is a clear difference in internal crack pattern and spreading deformation behavior according to shear reinforcement shape, and this influences the shear strength of the RC beam.

Heliyon, 2021

The shear behavior of reinforced concrete (RC) beams has been a major research area for a long time. Since the shear response of RC beams is affected by different factors, many researchers have reported that the nature of shear behavior is complicated. One of these factors worth investigating is the inclination of shear reinforcements. This paper investigated the effect of the orientation of stirrups on the shear capacity of RC beams as the shearspan-to-depth ratio (a/d) varies. The contribution of concrete compressive strength was also studied. An experimental program investigating 21 RC beams has been conducted. The test results revealed that the shear capacity increases as the arrangement of stirrup changes from conventional vertical arrangement to inclined arrangement. However, the increment is high in beams with (a/d) ratio of 2.2 than beams with (a/d) ratio of 2.6, which are relatively slender. Shear capacity also increases as concrete compressive strength increase, which shows that concrete contribution to the shear capacity of beams should be taken in to account. In addition to the experimental test, the beams were analyzed numerically by using a general-purpose finite element package, Abaqus. The shear capacity of reinforced concrete beams obtained from the numerical analysis is in a good agreement with the experimental result. The results obtained by numerical analysis and experimental tests are compared to analytically calculated values by using shear provisions of ACI 318-14 and EN-2. Both ACI 318-14 and EN-2 are generally conservative in predicting the shear capacity of RC beams. However, the conservativeness of these codes reduced as a/d ratio of the beams increase.

Hagos Welegebrial , 2016

ABSTRACT Upgrading of existing structures becomes necessity due to various reasons; some of those are revised design code and deterioration with time due to environmental effects. Design codes are constantly being revised in many countries including Ethiopia as new loading requirement dictates for higher strengths demanded of structural members like shear, flexure, axial and torsion. This study focuses on the shear capacity assessment and strengthening of shear critical RC beams. In this research eight RC beams were investigated. All beams have the same geometric dimensions and reinforcement ratio (a/d=3.11, ρ=0.01314). The beams were intentionally designed to fail in shear and a different type of shear strengthening was implemented for each RC beam by varying the configuration of the stirrups used for shear strengthening. The amount of shear reinforcement utilized for strengthening was kept constant. All the strengthening methods were found to enhance the shear strength of the control RC beams, with varying degree of efficiency. However, a beam strengthen with vertical leg stirrups inserted by drilled along depth of beam and confined using horizontal legs with parallel vertical legs configurations(beam type-3) were found to be the most effective type. Analytical simulation were done using a non-linear 3D finite element formwork using fixed-four way crack model where the path and time dependent constitutive laws for tension, shear and compression are rooted in (DUCOM-COM3D).The simulation result were found to reproduce the experimental results reasonably, verifying the reliability of the mode failure as well. Key words: RC beam, shear, strengthening, vertical legs, confinement

Journal of Advanced Concrete Technology, 2018

In order to enhancement accuracy of shear design of reinforced concrete (RC) beams, detail understanding of the shear resistance mechanism is required. This study evaluated the shear resistance mechanism of RC beams based on arch and beam actions by using three dimensional Rigid-Body-Spring-Method (3-D RBSM). Firstly, RC deep and slender beams with and without shear reinforcement failed in shear were tested to measure local behavior. Then, the validity of local behaviors obtained from 3-D RBSM was confirmed by comparing with the test results and the applicability of decoupling of shear resistance mechanism using simulated stress distribution was presented. Moreover, the contributions of arch and beam actions in RC beams until failure stage were investigated numerically by changing the shear reinforcement ratio and shear span to depth ratio and was compared with the current shear design recommendations in JSCE Standard Specification. As a significant finding, the numerical results upon the quantitatively evaluation of shear resistance mechanisms that the shear strength of RC beam could be evaluated without classification of deep beams and slender beams was presented.

Composites Part B: Engineering, 2016

The Embedded Through-Section (ETS) is a recent strengthening technique that has been developed to retrofit existing reinforced concrete (RC) elements with shear reinforcement deficiencies. This technique is based on the execution of holes drilled through the element cross section, in which steel or fiber reinforced polymer (FRP) bars are inserted and bonded to the surrounding concrete with an epoxy adhesive. An experimental program was carried out with RC T-cross section beams strengthened in shear using steel ETS bars. The influence of the inclination and shear strengthening ratio of ETS on the shear strengthening efficiency was evaluated, as well as the interaction of ETS bars with existing steel stirrups. Two different analytical models are presented in this paper in order to calculate the contribution of ETS to shear resistance. The first model follows an empirical approach (experimental-based approach), while the second model takes into account the physical and mechanical principles of the technique (mechanical-based approach). The predictive performance of both models is assessed by using the experimental results.

International Journal of Protective Structures, 2013

This study aims to investigate the dynamic shear failure behavior of reinforced concrete (RC) beams under rapid loading through an experimental study and set up a strut-and-tie model with loading rate effects to predict the dynamic shear capacity of RC beams. Thus, rapid loading test for 48 RC beams was performed, in which shear spanto-depth ratio, shear reinforcement ratio and loading rate were variable. The RC beams exhibited diagonal tension failure, shear compression failure and flexural failure depending on the shear spanto-depth ratio and the shear reinforcement ratio. The influence of loading rate on the maximum resistance is more significant for the RC beams failed in shear than for those failed in flexure. The strut-and-tie model with loading rate effects was developed, in which the thickness of the compression strut was formulated to be increased with an increase in loading rate. The developed strut-and-tie model was in good agreement with the experimental results.