Engineering implications of ground motions on welded steel moment resisting frame buildings

Although tall buildings are relatively few in the Los Angeles area, more than 150 buildings with welded steel moment resisting frames were significantly damaged during the 1994 Northridge Earthquake. The number of damaged buildings and the level of damage surprised many engineers and building officials. This study summarizes an analysis of free-field ground motions at the location of 228 buildings for which post-earthquake engineers' reports, as well as weld inspections, were available. The study shows how vulnerable the pre-Northridge type welds are during seismic events, and how typical geotechnical ground motion parameters such as PGA and PGV are useful in assessing damage levels. The study may be used to estimate average damage levels and/or probabilities of building damage, for the Northridge Earthquake in adjoining localities and may also be used to estimate damage thresholds for future earthquakes, or in zones affected by previous earthquakes, including the 1987 Whittier, and 1989 Loma Prieta earthquakes.