Reliability functions for earthquake resistant design

A unified approach is presented for the establishment of design conditions and acceptance criteria for performance objectives associated with different return intervals. A life-cycle optimization analysis is adopted for this purpose. Reliability and expected damage functions are defined both for individual seismic events and for a long-term framework. System reliability functions are determined by Monte Carlo simulation for a number of multistory frames, designed for different base-shear ratios and subjected to earthquakes of different intensities. Systematic trends are identified about the variation of the reliability index with the natural logarithm of the expected ductility demand of a reference system. These trends lead to the definition of seismic reliability functions that can easily be adapted for applications to reliability-based design. The problem of transforming the results of the optimization studies into codified rules for practical design is briefly discussed.