Development of new Los Angeles seismic analysis criteria for tall buildings-site-specific considerations

Abstract

Many tall buildings are planned and constructed in the city of Los Angeles. Significant building code changes as a result of recent earthquakes will complicate the design and plan checking for new buildings, not only in Los Angeles, but throughout all seismic regions in the United States and around the world. This paper reports on new efforts to develop seismic analysis criteria for Los Angeles. The initial efforts have been in the areas of the design basis ground motions, near-source effects on ground motions and building design, and the first yield limit state. A study of the design basis ground motions in the Los Angeles area indicates that the present code-defined level of ground motion may underestimate the seismic forces in design. Near-source effects would affect practically all of the heavily populated and built-up portions of Los Angeles due to the many known and suspected active seismic sources in the region. Studies of the group motions suggest that a return period of about 40 years may be reasonable to estimate the earthquake demand for the first yield limit state.