Abstract
The 1995 Hyogoken-Nanbu Earthquake caused severe damage to civil infrastructures, including buildings, roadways, railways, subways, port facilities and so on. The ground motions observed during the Hyogoken-Nanbu Earthquake were very strong and its intensity of ground acceleration was very large in all three components that are the North-South, East-West and Up-Down components, so that the complex spatial response of structures has been reported. It is strongly recommended that the development of the reliable seismic design methodology should be made based on the full understandings of the spatial behavior of structures subjected to 3D ground motions. A simple mass-spring-dashpot model for evaluating the response of structures subjected to bidirectional ground motions was proposed, wherein the elasto-plastic stiffness was defined based on the strength interaction curve in conjunction with basic principles of the theory of plasticity. The proposed simple model was shown to be capable of accurately predicting the bidirectional response of structures.
