Shear behaviour of reinforced concrete beams with confinement near plastic hinges

Abstract

The vast majority of structures, even in high-risk zones, will not actually be subjected to earthquake during their design lives. It is therefore felt that spiral binding is only likely to be used in practice if it can contribute to the static shear strength of the structure and so replace at least some of the stirrups. The question addressed here is whether such spirals are useful to carry shear in beams and in particular whether they can usefully improve the residual shear strength at hinges after severe cyclic bending.

Utilising confinement reinforcement for shear resistance in reinforced concrete structures

“…The predictions obtained by the Response program failed to give Utilising confinement reinforcement for shear resistance in reinforced concrete structures Jaafar a full explanation for the results attained in Jaafar (2008). It succeeded in simulating both the failure mode and the ultimate load for the beam with interlocking spirals.…”

“…Only stage one experimental results will be presented in this paper; more details can be found in Jaafar (2008) Experimental aims…”

“…From the experimental information presented in Jaafar (2008), it becomes apparent that beams in stage I (case of SB1, SB5, SC1, SC2, SC3 and SC4) were capable of carrying higher shear loads, despite the fact that spirals did not connect the tension and compression chord of the beams. It would appear, therefore, that it is not a necessary condition for beams with such shear reinforcement configuration to behave (at ultimate limit state) as a truss in order to resist the action of shear forces as the absence of such reinforcement within the tensile or compression zone precludes the transformation of the beams into truss (or, at least, into a full-depth truss).…”

“…To analyse the beams with spiral shear reinforcement presented in Jaafar (2008) and briefly described in Figure 1 and Figure 2, where the accuracy of the program is quite apparent.…”

Equivalent stress block for normal-strength concrete incorporating strain gradient effect

“…Failure due to shear would be very brittle and should be avoided in design (Baczkowski and Kuang, 2008;Bukhari et al, 2010;Choi et al, 2010;Lu et al, 2009). A precise estimation of the beams' flexural strength would also allow engineers to predict the locations of plastic hinges (Bai and Au, 2008;Jaafar, 2008;Pam and Ho, 2009) and hence the deformability (Ho and Pam, 2010;Sebastian and Zhang, 2008;Wu et al, 2004) of members under extreme events. Engineers may then correctly design and detail the reinforcement within the plastic hinge region for the required ductility and rotation capacity (Spence, 2008;Zhou and Zheng, 2010).…”