Effects of Site Conditions of Earthquake-Resistant Design of Structures

by Vitelmo V. Bertero, (F.ASCE), Univ of California at Berkeley, Berkeley, United States,
Eduardo Miranda, Univ of California at Berkeley, Berkeley, United States,

Document Type: Proceeding Paper

Part of: Structures Congress XII


After a brief discussion of the importance of reliable establishment of design Earthquake Ground Motions (EQGMs) for efficient Earthquake-Resistant Design (EQ-RD) of structures, this paper reviews how the effects of local site conditions are presently considered in the practice of EQ-RD. The paper then summarizes the results of a study in which linear and nonlinear response spectra for strength and displacement of a single-degree-of-freedom system (SDOFS) to 124 EQGMs recorded on different site conditions (rock, alluvium and soft soil) were computed and analyzed statistically. A comprehensive study of the strength reduction factors (Rμ) resulting from the nonlinear behavior shows that the Rμ are strongly influenced by site soil conditions, period of the structure (T), and amount of tolerable nonlinear deformation (represented by the ductility ratio, μ). Analysis of the results obtained in the study of linear and nonlinear spectra for displacement shows that the commonly-accepted practice of using linear elastic spectra to estimate inelastic displacement demands can lead to significant errors, particularly in the case of soft-soil EQGMs. Finally, the paper briefly discusses a promising new procedure for evaluating the damage potential of EQGMs based on an energy approach and the use of damage functions or damage indices.

Subject Headings: Load and resistance factor design | Structural reliability | Nonlinear response | Earthquakes | Elastic analysis | Soil analysis | Linear analysis | Soil strength

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