Seismic Design Forces for Rigid Floor Diaphragms in Precast Concrete Building Structures

Floor accelerations are needed to evaluate in-plane diaphragm forces in earthquake resistant design of buildings, and for the design of their connections. Recorded floor accelerations in buildings during some past earthquakes have shown acceleration magnifications that are not properly considered by current building codes. Earthquake damage in some precast buildings seems to point out significant deficiencies in the design of precast diaphragms. Two deficiencies stand out: the magnitude of the design forces and the lack of suitable design methods. This paper describes an experimental validation of a previously proposed analytical-based procedure for the evaluation of earthquake-induced floor horizontal accelerations in regular buildings built with rigid diaphragms. Horizontal floor accelerations recorded from shake table tests of four small-scale structures representing frame and frame-wall multistory reinforced concrete buildings were collected. These buildings were tested on the University of Illinois Urbana-Champaign shaking table during the 1979–1989 period. The horizontal floor accelerations obtained from the tests are compared in this paper with results from four predictive approaches.