LATERAL STIFFNESS – STRENGTH DISTRIBUTION AND DAMAGE CONCENTRATION ALONG THE HEIGHT OF A BUILDING

SUMMARY Most types of building damage during the 1995 Hyogo-ken-Nanbu Earthquake were similar to those caused by previous earthquakes, e.g. the damage in the soft first story. One of the features of the damage caused by the earthquake, however, was the mid-story collapse of medium-rise buildings. In this study, elasto-plastic analyses are carried out for MDOF models of various distributions of lateral stiffness and strength in order to investigate such damage. The building is idealized as a MDOF model, which has flexural springs at both ends of each column and the columns can rotate up to 90 degrees which means complete collapse. With this model we can analyze the response of structures subjected to horizontal and vertical motions simultaneously, taking into account P - ∆ effect. Input earthquake motions used for the analyses are El Centro (1940) and Kobe JMA (1995), etc. Different types of the lateral stiffness distribution are used in the analyses, e.g. (1) uniform stiffness distribution and (2) the stiffness distribution for which the fundamental mode shape is inverted triangular. Different types of the distribution of yield story shear coefficient are also used in the analyses, e.g. (1) Ai distribution of the Japanese code, and (2) the distribution in which the yield story shear coefficients of upper stories are sufficiently large so that the response of the upper stories remains in the elastic range and the response of lower stories exceeds the elastic limit. The analytical results of this study show that the deformation distribution along the height of a building is affected by the input earthquake motion, by the stiffness distribution, and especially by the distribution of yield story shear coefficient. This feature is emphasized for the input earthquake motion recorded during the 1995 Hyogo-ken-Nanbu Earthquake.