Evaluating second-order effects in rigid wall-flexible roof diaphragm buildings

Abstract

When evaluating seismically induced second-order effects in buildings, engineers and researchers are most familiar with these concerns in the context of multistory buildings with rigid diaphragms. However, similar concerns are valid for short single-story concrete or masonry-walled buildings with larger flexible diaphragms, which is a significant portion of the building stock in the United States. These rigid wall-flexible diaphragm (RWFD) buildings may have significant diaphragm drifts causing induced second-order effects. The stability coefficient currently found in ASCE 7 has traditionally been used by practitioners to evaluate the relative risk of P-delta instability in multistory buildings, but this indicator can be adapted for use in RWFD buildings. Using numerical studies following the Federal Emergency Management Agency (FEMA) P-695 collapse assessment methodology to evaluate the risk of collapse for a set of RWFD archetype buildings, a modified stability coefficient for RWFD buildings is found to capture the trend toward P-delta collapse and can act as a reasonable indicator without the need for heavy computational efforts.