Northridge Earthquake Effect on Manufactured Housing in California

This report describes the results of an investigation into the nature of manufactured home failures caused by the January 17, 1994 Northridge earthquake. The purpose of the investigation was to (1) assess the performance of manufactured home construction, foundations, anchoring systems, and utility and gasline connections; (2) assess the nature and amount of damage done to manufactured homes and compare this to the damage occurring to site-built, single-family homes in the same area; and (3) gather information that would provide the basis for recommendations on how to minimize the effects of earthquakes on manufactured homes. The investigation found that many manufactured homes were shifted off their foundation supports and that although structural damage was usually isolated to floor and underfloor areas, lateral movement and shifting also damaged gas and electrical utility connections, in some cases causing devastating fires. The report also found that homes that did not have an earthquake resistant bracing (ERB) system were more severely damaged than units that were equipped with such systems, but there was a great deal of variance in the performance of ERB systems. The system generally limited the vertical downward movement of the home to two inches and significantly reduced the horizontal movement. Based on these conclusions, the report recommends that HUD encourage States and localities to adopt installation standards to minimize earthquake damage by the installation of ERB systems or other lateral- load restraint methods and that HUD consider establishing design provisions and Standards to evaluate the adequacy of connections between heat producing appliances (such as hot water heaters) and the manufactured home to resist seismic forces and resulting displacements.

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