Damage Analyses of Imperial County Services Building

The failure of the Imperial County Services Building in El Centro, California, during the Imperial Valley Earthquake on October 15, 1979 is examined. The event was exceptional insofar as a modern reinforced concrete building, designed to comply with a recent code, extensively instrumented and previously subjected to dynamic testing, was severely damaged. Available records of measured dynamic characteristics and traces of the motions induced by the earthquake in both the adjacent ground and the structure, enable critical analyses to be made of the failure modes. Building configuration and composition are summarized, together with the strong motion records obtained during the earthquake. A three‐dimensional mathematical model of the building is developed and the results of computer analyses are presented. Elastic analyses are used as a basis of justifying the model and both elastic and non‐linear three‐dimensional time history analyses are described. Good correlation between analytical results and field observations is established. In particular the combined effect of biaxial moment and axial load in causing ground floor column failure is demonstrated.