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FOREWORD Highway administrators, engineers, and researchers often face problems for which infor- mation already exists, either in documented form or as undocumented experience and prac- tice. This information may be fragmented, scattered, and unevaluated. As a consequence, full knowledge of what has been learned about a problem may not be brought to bear on its solution. Costly research findings may go unused, valuable experience may be overlooked, and due consideration may not be given to recommended practices for solving or alleviat- ing the problem. There is information on nearly every subject of concern to highway administrators and engineers. Much of it derives from research or from the work of practitioners faced with problems in their day-to-day work. To provide a systematic means for assembling and evaluating such useful information and to make it available to the entire highway commu- nity, the American Association of State Highway and Transportation Officials--through the mechanism of the National Cooperative Highway Research Program--authorized the Transportation Research Board to undertake a continuing study. This study, NCHRP Proj- ect 20-5, "Synthesis of Information Related to Highway Problems," searches out and syn- thesizes useful knowledge from all available sources and prepares concise, documented reports on specific topics. Reports from this endeavor constitute an NCHRP report series, Synthesis of Highway Practice. This synthesis series reports on current knowledge and practice, in a compact format, without the detailed directions usually found in handbooks or design manuals. Each report in the series provides a compendium of the best knowledge available on those measures found to be the most successful in resolving specific problems. PREFACE This study identifies and describes current practice and available methods for evaluating the influence of local ground conditions on earthquake design ground motions on a site- By Jon M. Williams specific basis. Information includes criteria used to determine when a site-specific analysis Program Director is needed, how to develop input parameters required for a site-response analysis, the nature Transportation of the site-response analysis performed (equivalent-linear, total stress nonlinear, effective- Research Board stress nonlinear), the process of model setup, and how uncertainties are dealt with in the analysis process. Information was gathered by a literature review and a survey of state departments of transportation and selected academics. Neven Matasovic, Geosyntec Consultants, Huntington Beach, California, and Youssef Hashash, University of Illinois at Urbana-Champaign, collected and synthesized the infor- mation and wrote the report. The members of the topic panel are acknowledged on the pre- ceding page. This synthesis is an immediately useful document that records the practices that were acceptable within the limitations of the knowledge available at the time of its preparation. As progress in research and practice continues, new knowledge will be added to that now at hand.

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