TORSION EFFECT DUE TO ASYMMETRIC SEISMIC POUNDING BETWEEN MULTISTORY BUILDINGS

Abstract eng:
Earthquake induced collisions between adjacent structures have been repeatedly reported in the literature as a frequent case of damage. It is quite usual seismic induced oscillations of a structure in a block of buildings to be partly restrained in lateral displacements and therefore a torsional movement to be introduced in the building during an earthquake excitation. Further it has been repeatedly observed that torsion is a critical factor leading in many occasions to major structural damage or even complete collapse during strong ground motions. Seismic damage surveys and relevant analyses conducted on modes of failure of building structures during past severe earthquakes have concluded that among the most damage susceptible structures are those that exhibit torsional behavior. In this work the case of reinforced concrete multistory buildings that suffer pounding in a non-symmetric way is studied. Pounding occurs only in one (case 1) or two (case 2) columns of the structure whereas the other columns are free to move without restrictions. This way torsional oscillations are introduced in the structural system during a seismic excitation. Nonlinear dynamic step-bystep analysis and special purpose elements are employed for the needs of this study. More than fifty pounding cases with torsional effect between structures with different total height for three excitations are studied and results in terms of displacements, torsional rotations, ductility requirements are presented and commented. The influence of the size of the gap distance between the adjacent structures on the torsion effect is also investigated. The results clearly show that high capacity requirements in terms of torsional moments, column shear strength and ductility are developed due to the asymmetric pounding.

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