A comparative study of seismic diaphragm design forces for RC dual system buildings

Abstract

The reinforced concrete (RC) diaphragm damage observed during the Northridge earthquake (1994) has motivated numerous analytical and experimental studies focused on evaluating the seismic performance of this important building component. The ASCE/SEI 7-16 recently introduced an alternative methodology to determine diaphragm design forces that considered various diaphragm systems. However, this formulation was developed for typical North American structures (on frames or dual systems combined with gravity framing), which substantially differ from other worldwide common typologies that may not include gravity framing. Throughout this study, the accuracy of the existing code provisions and other alternative methods is evaluated by using three-dimensional computer models of eight symmetric-plan reinforced concrete buildings that are between five and 15 stories high and have non-gravity frames (i.e. all frames are part of the seismic force resisting system) for RC-floor systems. These models are subjected to non-linear response history analysis that considers sets of far-field records. Benchmark values, defined as the mean value of the time responses and their dispersion, are compared with the forces of design codes and procedures. General conclusions indicate that existing provisions underestimate diaphragm design forces for all the systems considered, but the results can substantially improve if a low diaphragm reduction factor is used. Alternative procedures capture the magnitude but not the height distribution. Finally, the level of non-linear behavior of the structural elements was verified; beams exhibit high inelastic response, but the overall structure and the vertical elements mostly kept elastic.