Dealing in Practice with Selecting and Modifying Earthquake Ground Motions for Nonlinear Analysis

Nonlinear earthquake analyzes of structures are increasingly required by building codes and other seismic design regulations. An essential component of these analyses is that the geotechnical engineer has to provide the structural engineer with a set of strong motion time histories, typically three or seven sets containing two orthogonal horizontal components, and one vertical component if needed. The procedure for selecting the seed time histories and modifying them to match the design response spectrum involves several steps including development of seismological criteria, earthquake deaggregation analysis, and spectral matching. This procedure for selecting and modifying earthquake ground motions is explained based on three example projects in the San Diego region; i.e., seismic retrofit of an existing hospital complex, seismic retrofit of an existing historic bridge, and seismic design of a harbor facility. Challenges and identified issues encountered in practice will be discussed and some suggestions will be proposed