Investigation of Alternative Seismic Design Procedures for Standard Buildings

Abstract

The seismic design provisions of most building codes in the United States specify ground motion parameters
\nfor various regions of the country and provide simple formulas to determine a distribution of lateral
\nforces for which the structure should be designed. The simple formulas typically involve the use of one or
\nmore "factors" to account for anticipated inelastic behavior of the structure, relative importance of the
\nstructure, and site soil effects. Although these code provisions are very simple to use, they oversimplify a
\ncomplex problem and are based on many implicit assumptions which many designers may not appreciate.
\nFurthermore, the reliability of the final design is not known. An alternative design and analysis procedure,
\nin which the underlying assumptions are more clearly defined and which provides a more uniform
\nlevel of reliability in the final design, is presented. The procedure requires the designer to consider two
\nlevels of earthquake excitation. "Equivalent" single-degree-of-freedom models and uniform hazard response
\nspectra are used to evaluate structural performance. Deterministic design-checking equations are
\nderived based on displacement-based performance criteria which are expressed in probabilistic terms.
\nThe deterministic design equations account for the uncertainty in predicting site soil effects, the uncertainty
\nin seismic hazard, and the approximate nature of the simplified models of the structure through the use
\nof design factors. The goal of the alternative procedure is to enable designers to achieve code-specified
\ntarget performance objectives for moderate and severe levels of earthquake excitation.