ACI 421.2-21 Seismic Design of Punching Shear Reinforcement in Flat Plates—Guide

ACI 421.2-21 Seismic Design of Punching Shear Reinforcement in Flat Plates—Guide. 3.1 —Lateral-force-resisting systems In Seismic Design Categories (SDCs) D. E, and F. flat plate buildings need to rely on a lateral-force-resisting system that limits lateral displacement. Flat plates will experience the same lateral displacemenb as the lateral-Ibrue-resisting system and should be designed to do so without losing their capability to support gravity loads during or after an earthquake. The lateral-fbrce-resisting system should have sullicient stillness to control the lateral displacement of the structure and limit the maximum lateral story drift to the values prescribed by the general building code, as discussed in Section 3.2. The story drift ratio is defined as the story drift divided by the story height. The story height is defined as the distance between the midsurfaces of the consecutive flat plates at the top and bottom of the story of interest. Moments due to design displacements arc transfirred between slabs and columns and are a direct result of the lateral displacement experienced by the entire building. The transfer of shear Ibrues , and moment increases the risk of a punching shear failure during an earthquake. ACI 352.1R provides connection design recommendations for flat plate-column frames and considers that such frames may be adequate as the lateral-force-resisting system in regions of low and moderate seismic hazard. This guide excludes the selection or the design of the lateral-Ibreeresisting systems; it includes the punching shear design of flat plates. with and without shear reinforcement, subjected to gravity loads combined with moment M.,, , induced by the lateral drill of the flat plate-column connections. 3.2—Limits on story drift ratio It has been recommended that flat plate structures should have the capability to withstand a design story drift ratio of at least 0.015, including inelastic delbrmations (Sozen 1980; ACI 352.lR: Pan and Moehle 1989). In the force-based design approach. a static elastic analysis of the lateral-force-resisting system is performed to determine the elastic story drill , (due to forces specified in ASCESEI 7). This value is then multiplied by factors, also given in ASCE/SEI 7, to obtain the design story drill 6.,. ASCEJSEI 7 requires that the calculated 8 (depending on the lateral-force-resisting system and the SDC), including inelastic deformation, not exceed 0.007 to 0.025 of the Story height. The code also requires that the fiat plate-column connection be adequate to carry the vertical load and the induced moments and...