ACI 421.2R

Abstract

In seismic design, the displacement-induced unbalanced moment and the accompanying shear forces at flat platecolumn connections should be accounted for. This demand may be effectively addressed by changes in dimensions of certain members, or their material strengths (for example, shear walls and column sizes), or provision of shear reinforcement or a combination thereof. This guide does not address changes in dimensions and materials of such members, but focuses solely on the punching shear design of flat plates with or without shear reinforcement. <br>This guide, supplemental to ACI 421.1R, focuses on the design of flat plate-column connections with or without shear reinforcement that are subject to earthquake-induced displacement; reinforced concrete flat plates with or without post-tensioning are treated in the guide. Slab shear reinforcement can be structural steel sections, known as shearheads, or vertical rods. Although permitted in ACI 318, shearheads are not commonly used in flat plates. Stirrups and shear stud reinforcement (SSR), satisfying ASTM A1044/A1044M, are the most common types of shear reinforcement for flat plates. Shear stud reinforcement is composed of vertical rods anchored mechanically near the bottom and top surfaces of the slab. Forged heads or welded plates can be used as the anchorage of SSR; the area of the head or the plate is sufficient to develop the yield strength of the stud, with negligible slip at the anchorage. The design procedure recommended in this guide was developed based on numerical studies (finite element method) and experimental research on reinforced concrete slabs subjected to cyclic drift reversals that simulate seismic effects. The finite element analyses, supplemental to the experimental research, used software, constitutive relations, and models that were subject to extensive verifications by comparing the results with the behavior observed in tests (Megally and Ghali 2000b). <br>Structural integrity reinforcement near the bottom of the slab extending through the columns should be provided as required by ACI 318. This document supplements ACI 352.1R and ACI 421.1R, which, respectively, include recommendations such as extending a minimum amount of bottom integrity reinforcement through the column core and provide details of design for shear reinforcement in flat plates. ACI 352.1R also provides recommendations for the design of flat plate-column connections without slab shear reinforcement subjected to moment transfer in the inelasticresponse range. The equations of this guide predict punching shear strength and drift capacity, assuming that adequate flexural reinforcement is provided at the flat plate-column connections; the present guide does not address the required flexural reinforcement.