Title: Requirements for Seismic-Resistant Flat Plates: Strength and Ductility

Author(s): Amin Ghali and Ramez B. Gayed

Publication: Symposium Paper

Volume: 287

Issue:

Appears on pages(s): 1-20

Keywords: column; drift; ductility; earthquake; flat plate; flexure; punching shear; seismic; strength.

DOI: 10.14359/51683855

Date: 5/1/2012

Abstract:
Lateral displacement of multi-story flat plate concrete buildings in an earthquake induces moment reversals between columns and slabs. The amplitude of the transferred moment depends upon the story drift, defined as the displacement of one floor relative to the floor above or below. Flat plate buildings must have a lateral force-resisting system that limits the design story drift ratio to 0.025; where the design story drift includes plastic deformation and is defined as the design story drift divided by the distance between the mid-surfaces of the flat plates of two consecutive floors. The moments transferred from the columns to the slabs have to be resisted by flexural and shear reinforcements, whose magnitudes and detailing provide the slabs with the strength and the ductility to undergo the design story drift without failure. The design of shear reinforcement for the moment transfer in an earthquake, as required by ACI 318, considers either the strength or the ductility, not both. ACI 421.2R-10 recommends and justifies a design procedure for the shear reinforcement providing the strength as specified by ACI 318; in addition, it recommends a minimum amount and extension of shear reinforcement that provides a level of ductility adequate for a design-story drift ratio = 0.025 (the upper permissible level in several codes). The design procedure is presented with examples.