Seismic Evaluation and Upgrading of Existing Steel Concentric Braced Structures

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9416184 Goel The primary objective of this research project is to develop methods for evaluation and upgrading of existing "non- ductile" (ordinary) concentric braced frame structures of steel for survival during future earthquakes. Whereas, widespread connection failures in steel moment frames due to the Northridge earthquake were quite unexpected, it is also generally recognized that concentric braced frames (CBF) are among the most efficient and popular structural systems in steel for lateral load resistance. There exists a large inventory of these structures which are potentially hazardous. A significant number of such structures suffered widespread damage during the Northridge earthquake and required extensive repair and upgrading work. Current or past design practice and codes did not focus on providing ductility in these structures previously studied. The Northridge experience has emphasized the need for developing methods for evaluating and upgrading existing CBF in order to ensure satisfactory performance during future more severe probable earthquakes. Two theme structures are selected for the study. The four story building in North Hollywood which suffered the most dramatic failures and which represents the typical CBF structures designed by modern codes and practice has been chosen for detailed investigation including correlation of the results with observed damage. The second part of this project is devoted to the development of practical and effective upgrading schemes to mitigate future earthquake hazard. This is a Northridge earthquake project. ***