ACI 421.1R-08 Guide to Shear Reinforcement for Slabs

ACI 421.1R-08 Guide to Shear Reinforcement for Slabs.
Several types and configurations of shear studs have been reported in the literature. Shear studs mounted on a continuous steel strip, as discussed in the main text of this report, have been developed and investigated (Dilger and Ghali 1981; Andrä 1981; Van der Voet et al. 1982; Mokhtar et al. 1985; Elgabry and Ghali 1987; Mortin and Ghali 1991; Dilger and Shatila 1989; Cao 1993; Brown and Dilger 1994; Megally 1998; Birkle 2004; Ritchie and Ghali 2005; Gayed and Ghali 2006). Headed reinforcing bars were developed and applied in Norway (Dyken and Kepp 1988) for high-strength concrete structures, and it was reported that such applications improved the structural performance significantly (Gayed and Ghali 2004; Hoff 1990). Another type of headed shear reinforcement was implemented for increasing the punching shear strength of lightweight concrete slabs and shells (McLean et al. 1990). Several other approaches for mechanical anchorage in shear reinforcement can be used (Marti 1990; Muller et al. 1984; Mart et al. 1977; Ghali et al. 1974). Several types are depicted in Fig. A.1. ACI 318 permits stirrups in slabs with d ≥ 6 in. (152 mm), but not less than 16 times the diameter of the stirrups. In the stirrup details shown in Fig. A.1(a) (from ACI 318), a bar has to be lodged in each bend to provide the mechanical anchorage necessary for the  Fig. A.1—Shear reinforcement Type (a) is copied from ACI 318. Types (b) to (e) are from Dyken and Kepp (1988), Gayed and Ghali (2004), McLean et al. (1990), Muller et al. (1984), and Ghali et al. (1974).
CHAPTER 3—ROLE OF SHEAR REINFORCEMENT Shear reinforcement is required to intercept shear cracks and prevent them from widening. The intersection of shear reinforcement and cracks can be anywhere over the height of the shear reinforcement. The strain in the shear reinforcement is highest at that intersection. Effective anchorage is essential, and its location should be as close as possible to the structural member’s outer surfaces. This means that the vertical part of the shear reinforcement should be as tall as possible to avoid the possibility of cracks passing above or below it. When the shear reinforcement is not as tall as possible, it may not intercept all inclined shear cracks. Anchorage of shear reinforcement in slabs is achieved by mechanical ends (heads), bends, and hooks. Tests (Marti 1990) have shown, however, that movement Fig. 3.1—Geometrical and stress conditions at bend of shear reinforcing bar.
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