Mitigation of earthquake hazards in unreinforced masonry buildings: Issues and the implementation of public policies.

摘要

For more than fifty years various state agencies have recognized the hazards associated with California's forty thousand to fifty thousand unreinforced masonry (URM) buildings as the state's single greatest threat to life safety in an earthquake. As a result of the Seismic Safety Commission's concerted effort to reduce these hazards, the Unreinforced Masonry Building Law (URM Law) was enacted in 1986, mandating that each local jurisdiction in seismic zone 4 identify and inventory all potentially hazardous URM buildings and establish a hazard-mitigation program for them. Over a million Californians live and work in such buildings in zone 4, the area of highest probability and intensity of earthquakes. Seismic-safety professionals estimate that unless these buildings are strengthened, one in five occupants will die if the buildings collapse in an earthquake. Structural failure of URM buildings during the 1989 Loma Prieta earthquake killed eight people; in San Francisco alone, fifty miles from the epicenter, 1,947 URM buildings were damaged, some severely.; The Seismic Safety Commission reported in June 1990 that 42 percent of local jurisdictions had substantially complied with the URM Law (completing building survey inventories and establishing mitigation programs) by the deadline of January 1, 1990.; The road is long to the actual rehabilitation or demolition of these potentially hazardous buildings. Public policies, programs, and the several issues and obstacles affecting implementation of the policies and programs are examined: (1) Social and economic impacts of programs; (2) Lowered structural standards (not meeting current earthquake code); (3) Liability of local governments for earthquake hazards; (4) Earthquake insurance, a public policy dilemma; (5) URM building owners' financing difficulties; (6) High construction costs of URM building strengthening; (7) Loss of low-rent housing that URM building strengthening programs may generate; (8) Variation in URM strengthening standards by local governments; (9) Proposed base isolation system as a new, effective approach to the rehabilitation of hazardous buildings in lieu of the limited conventional procedure; (10) Recommendations for resolving and eliminating various issues and obstacles to URM building programs.