Spatial component analysis of 3-d displacement and storey-drift envelopes of r.c. buildings under seismic loads

Abstract eng:
Design and seismic assessment of structures based on the attainment of a specified performance state, defined by strain or drift limits, is a new concept. Knowledge of the spatial characteristics of the deformed shape of the structure at the state of its maximum response is of extreme significance for establishing deformation demands in the context of displacementbased seismic assessment or redesign. Furthermore, the knowledge of the structure’s deformed shape is necessary for the design and attachment of secondary systems (i.e. natural gas transmission pipelines), whose seismic response is multiply excited through the displacements at the point of the building where they are attached. This paper investigates the spatial envelope of the building’s displaced shape and the threedimensional distribution of drift for R.C. buildings, with and without irregularities in plan and in height, at the time of their maximum seismic response. Elastic and inelastic Incremental Dynamic Analyses have been carried out, with parameters of investigation being the structural configuration, the earthquake PGA and frequency content. The approximate displacement envelope of the structure’s seismic response is determined as a linear combination of the translational fundamental shapes in the two orthogonal directions of the plan and the pure mode of rotation, calculated by vibration-analysis procedures in the corresponding directions. This enables simple component analysis of the dynamic response of the structure, where, depending on the orientation of the ground motion, the participation of the components is estimated and used to establish the envelope of displacements and interstorey drift of the structure in space. The finding is tested and confirmed in the numerical output of calculated responses.

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