Rotations in a shear beam model of a seven-story building caused by nonlinear waves during earthquake excitation

摘要

We model a seven-story, reinforced-concrete building in Van Nuys, CA, which was damaged during theud1994 Northridge earthquake. We use a one-dimensional, layered, shear-beam model with bi-linear materialudproperties, and we examine how the rotations (local strains and drifts) in this model depend upon theuddistribution of the stiffness along the building height, the nonlinear properties of the reinforced concrete,udand the nature of strong motion. We show how, following the powerful waves propagating up and downudthe building, point rotations take place that differ from the corresponding average drift angles. These pointudrotations are larger near the rigid floor slabs (near the top and bottom ends of the columns, shear walls,udand nonstructural members found at all floors) and propagate as slow waves up and down the building.udThese slow rotational waves occur only while the material is experiencing large nonlinear deformations,udand their amplitudes grow with ductility. We note that recording these rotational waves in real time mayudprovide a powerful new vehicle for health monitoring of full-scale structures excited by large transientudforces when their structural members enter large nonlinear deformations.