One-Way Shear Resistance of RC Members with Unconnected Stirrups

Abstract

This paper presents results of eight experimental tests carried to evaluate the mechanical performance of unconnected "W" stirrups.Reinforced concrete wide beams were tested and their characteristics were idealized to represent column strips in flat slab buildings. The main variables were: the type of shear reinforcement; the shear span to effective depth ratio (av/d); and the flexural (ρl) and shear (ρw) reinforcement ratios. In general, both the response and the shear resistance of the structural elements with unconnected "W" stirrups was similar to those elements with vertical closed stirrups. Increments of shear resistance of up to 84% were achieved, indicating that they have high potential for use as shear reinforcement in slab-column connections.

Influence of the supplementary reinforcement on the shear strength of beams with prefabricated truss stirrups

“…It was observed that all tested beams had an ultimate strength lower than the estimated flexural strength, contributing to the understanding that the specimens' failure was related to shear. Concerning the comparison with the reference beam, all specimens showed a significant increase in strength, varying between 89% and 158%, showing that the prefabricated truss stirrups contribute to the increase in shear strength, as observed by Ferreira et al [22]. The beams with supplementary reinforcement at both end showed greater strength than the specimens with the u-hooks only on the tensile face.…”

“…The longitudinal reinforcement was kept constant for all tested beams, consisting of 7 bars of 25 mm in diameter in the tensile area and 7 bars of 12.5 mm in diameter in the compression area. The shear reinforcement used in this study was composed of prefabricated truss stirrups, developed by Ferreira et al [22], manufactured in modules and installed between the bottom and top flexural reinforcement shown in Figure 4a. In addition to the transverse reinforcement, u-hook-shaped delamination control reinforcement was used, according to the model adopted by Tapajós [13], as shown in Figure 4b.…”

“…Concerning the shear reinforcement, two SG were attached to each instrumented bar, choosing to instrument the layers arranged in the middle of the shear span, where it is estimated that the greatest strains in transverse reinforcement occur, as observed by Ferreira et al [22] and Tapajós [13]. SG were also used in the supplementary reinforcement to observe its behaviour during the test.…”

“…Even so, it is possible to mention studies where the use of shear reinforcement with internal anchorage had satisfactory performance, and the development of cracks by delamination was not observed in some papers [19][20][21]. It is also worth mentioning the study of Ferreira et al [22], who tested prefabricated truss stirrups with internal anchorage in reinforced concrete wide beams, observing the delamination in some specimens. However, Tapajós [13] tested the shear reinforcement developed by Ferreira et al [22] with and without the addition of a u-hook as supplementary reinforcement to avoid delamination, noting that it would be possible to obtain a performance similar to that of beams with closed stirrups anchored to flexural reinforcement and studs.…”

Experimental analysis of punching shear in flat slabs with variation in the anchorage of shear reinforcement

“…Although various types of shear reinforcement have been shown to increase punching resistance capacity and increase the ductility of slab-column connections, in comparison to similar slabs without shear reinforcement, [36][37][38][39][40][41][42] the normative requirements of ACI 318, 43 ACI 421.1R, 44 Eurocode 2, 45 ABNT NBR 6118, 46 and the recommendations of the fib Model Code 2010 47 determine that the reinforcements should be well anchored. More specifically, in the case of stirrups, ACI 318 42 mentions that shear reinforcement should involve the flexural reinforcement in the direction of the detailing.…”