Influence of stirrup spacing on shear resistance of reinforced concrete beams

Abstract

This study investigates the behaviour of, and evaluates the benefit accruing to, shear critical reinforced concrete beams, when provided with vertical stirrups spaced at decreasing intervals along the axis of the beam, but with the same amount of web reinforcement per unit beam length. Tests are carried out on three reinforced concrete beams, identical in geometry, flexural reinforcing, amount of web reinforcement per unit span length, material properties and test details. The only varable is vertical stirrup leg spacing along the span. The beams are loaded at half point on a simple span of 2500 mm and all fail in shear. Experimental results demonstrate that, as stirrup spacing decreases, there is a strength gain at ultimate. Besides increased carrying capacity, closer spacing of shear reinforcement results in more beneficial deformational characteristics. Transverse deflections and crack widths decrease as stirrup spacing decreases. The test results establish the desirability of using stirrup reinforcement in practice at as close an interval as possible, along the member length, keeping the amount of web reinforcement per unit length unaltered. This beneficial aspect of using closer stirrup leg spacing than the maximum permitted by codes is not found in the available national building codes for structural concrete. Notation d effective depth of the beam f 1 c cylinder compressive strength (psi) Research significanceAn accurate mathematical model to represent shear in concrete structures is still elusive, despite many decades of experimental research and the use of highly sophisticated analytical tools. Consequently, shear design of concrete beams remains empirical. The search for better design methods is still a preoccupation of many researchers. Research on simpler, more convenient and effective stirrup detailings than the conventional closed stirrups has been meagre to date. Behra and Rajagopalan (1969) pioneered notable research in this area. In three beams, in place of conventional closed stirrups, two-piece stirrups were tried. Lap in one beam was provided in the top face, but adequate development length was not there, with the wrong assumption that maximum stress occurred only at the stirrup mid-height; failure was at 95% of its rated shear. In another beam, lap was provided on the side faces and a lap length of 171 mm for 6-mm stirrups was not adequate; it was reported to fail at 89% of total strength. The final conclusion was that the slight loss of ductility and strength in the two-piece stirrup could be taken care of by more effective lap length.

Numerical and analytical evaluation of stirrup-induced confinement on resistance of RC beams using lower bound limit analysis

“…In this section, the numerical model results are compared with the experimental ones to validate the proposed element. Evaluation is on the beams tested by Murty and PapaRao (2013) and Latha et al (2018). These tests are designed such that the amount of stirrup force per unit length of the beam (Asfys/S) remains constant, but the distance between stirrups is varied.…”

“…Although the maximum allowable distance is specified in these design codes, they are silent about the effect of stirrup spacing at a distance less than permitted maximum restrictions. Experimental results on RC beams with the same Malayer University, Malayer, Iran reinforcement per unit length have shown that the use of stirrup with a larger diameter and larger space could significantly reduce the bearing capacity of RC beams (Murty and PapaRao, 2013;Latha et al, 2018). As the amount of shear reinforcement of specimens was constant, the reason for the reduction of the bearing capacity of the beams has stated the decrease of stirrup confinement.…”

Experimental study on effect of length of service hole on seismic behavior of exterior precast beam–column connections

“…The service hole was 40‐mm thick considering construction conditions. Closed stirrups, whose nominal yield strength was 235 MPa, were placed in spacing of 100 mm in the members, except the reduced spacing of 50 mm in the joint region, since densified closed stirrup arrangement effectively helps improve shear resistance and cracking behaviors of reinforced concrete beams and columns …”

A new ductile moment-resisting connection for precast concrete frames in seismic regions: An experimental investigation

“…The results of their study indicate that the reinforcement anchorage does not have a significant effect on the shear capacity of RC beams. However, several studies showed that the shear behaviour and cracking strength of RC beams can be considerably improved by using closed-stirrups and/or decreasing the stirrup spacing [22,23]. Most of the previous studies concluded that the precast beam-column connections can be detailed as strong as conventional monolithic connections.…”