Modeling of Building Diaphragms for Nonlinear Response- History Analysis

The seismic design of building diaphragms is one of the most vexing tasks today. Diaphragms are the structural elements primarily designed to transfer in-plane forces to the lateral force-resisting system. Design challenges increase when modeling diaphragms in nonlinear response-history analyses. The main complexity lies in choosing a computationally efficient model and establishing the demands and force distribution throughout the diaphragm. This paper describes two commonly used methods and compares the results in the design forces. A reinforced concrete core-wall building with a flat-slab transfer diaphragm is presented as a case study. Diaphragms were modeled with linear shell elements and the stringer-panel model. Differences in the magnitude of the forces are not significant, although visible differences are observed in the presentation of the results. The stringer-panel model shows a clear and unambiguous load path for the in-plane forces, making it an attractive alternative for the analysis of diaphragms.