ATC-50, Seismic Grading and Retrofitting Project for Detached Single-Family Wood-Frame Dwellings

Prompted by high economic losses from the 1994 Northridge, California, earthquake, the City of Los Angeles initiated a program to develop, test, and implement standardized procedures for the seismic evaluation and retrofit of single-family wood-frame dwellings (ATC-50 project). The primary products of the project include: 1) a seismic evaluation and grading system that considers damage or collapse potential in a manner that is consistent and useful to owners, purchasers, insurers, lenders, contractors, design professionals, and regulatory officials; 2) a seismic grading form that enables a certified inspector to evaluate a detached single-family wood-frame dwelling and assign a seismic grade, ranging from A through D, with each grade representing an expected range of damage (expressed as a percentage of replacement cost), should the 475-year MMI (Modified Mercalli Intensity) occur in the zip code containing the inspected dwelling; 3) seismic rehabilitation guidelines comprised of prescriptive methods, simplified engineering methods, and fully engineered methods that allow for a revised resistance grade; and (4) a report that provides guidance on how to develop and implement a market-driven, incentives-based program to induce homeowner use of earthquake performance evaluation forms and rehabilitation guidelines produced by the ATC-50 Project. The procedures were tested in a pilot program involving evaluation and grading of approximately 500 detached single-family wood-frame dwellings in the Los Angeles area, and rehabilitation (or retrofit) of approximately 50 dwellings with inadequate earthquake resistance. The ATC-50 project was conceived with input from the banking and insurance industries, was performed by the Applied Technology Council for the City of Los Angeles, and was funded by the Federal Emergency Management Agency through a Hazard Mitigation Grant Program award from the California Office of Emergency Services (now the California Emergency Management Agency). Additional funding for the 50 retrofit projects was provided through a grant from the U.S. Department of Housing and Urban Development.