The Jan. 17, 1995, Hyogoken-Nanbu Earthquake was one of the worst disasters to hit Japan in almost half a century. It has been compared in its impact to the great Kanto (Tokyo) Earthquake of 1923. The Kobe-Osaka region held many similarities in its geologic and tectonic setting to many areas along the West Coast, and possibly, other areas of the U.S. A geotechnical reconnaissance to identify the relevant problems and issues was organized. This report provides a timely, first-hand overview of the type and extent of the geotechnical aspects of the damage.

The collapse of the Cypress Street Viaduct during the 1989 Loma Prieta earthquake emphasized the vulnerability of elevated freeway bridge structures. A part of the joint Caltrans and University of California at Berkeley research project, initiated after the earthquake, focused on the outrigger knee joint systems found in bents of elevated freeway bridges. The investigation had two principal goals: to evaluate the behavior of the existing outrigger knee joint systems under a combined transverse and longitudinal loading and to devise and experimentally verify strategies for seismic upgrading of existing outrigger knee joints. The experiments on two half-scale as-built models confirmed the poor performance of existing outrigger knee joint systems observed after the earthquake. Two seismic upgrading strategies, a "ductile" and a "strong" strategy, were proposed and tested on prototype specimens. The "strong" strategy was chosen for the final seismic upgrade design. The variation of this strategy using a steel jacket, was recommended in the seismic upgrade design guidelines.

The feasibility of accelerating the discovery of new knowledge on the seismic behavior and response of the built environment and the complex civil infrastructure systems comprising major urban centers, and of synthesizing, transferring and utilizing this knowledge effectively in mitigating the potential life, physical, social and economic losses resulting from a major urban earthquake was explored at a bilateral Workshop convened in Maui, Hawaii during December 14 through 16, 1995. The 51 participants at the workshop were selected from leading experts from Japan, the U.S. and elsewhere in a wide variety of disciplines from engineering, social science and public policy research. The objective of this Workshop was to identify a research agenda related to urban earthquake loss reduction through a synthesis of available knowledge about the Hyogoken, Nanbu and Northridge earthquake disasters.

A comprehensive investigation of the Multiple Support Response Spectrum (MSRS) method for seismic analysis of bridges and other multiply supported structures is presented. The method accurately accounts for the spatial variability of ground motions, including the effects of incoherence, wave passage, and spatially varying site response. The structural response is obtained in terms of response spectra and peak displacements at individual support degrees of freedom, and a coherency function that characterizes the three spatial variability effects. Special attention is given to the effect of site response arising from variation in the soil conditions at different supports of the structure. Through extensive comparisons with time history analysis, the validity of the MSRS rule and the site response component of the coherency function are established. Methods for estimating the site frequency response function, needed in the coherency model, are developed and examined. These models and rules are implemented in the MSRS code for application to three-dimensional, multiply supported structures. Using the MSRS code, extensive parametric studies are performed for two example bridge structures. The report concludes with a summary of guidelines for practical implementation of the MSRS rule.