The Earthquake Engineering Online Archive

Earthquake analysis of structure-foundation systems

Vaish, Ashok K.; Chopra, Anil K.

UCB/EERC-73/09, Earthquake Engineering Research Center, University of California, Berkeley, 1973-05, 138 pages (535/V16/1973)

A computationally efficient procedure for the linear earthquake analysis of structure-foundation systems is developed, which is specially suited to finite element solutions of complex shaped structures on large, layered foundations. The procedure is very general in scope, being applicable to a large variety of structure-foundation interaction problems. An explicit formulation of the procedure is presented for a plane-strain idealization of a dam-foundation system. The procedure utilizes a substructure approach. The foundation is analyzed, first, independently of the structure to obtain its frequency dependent compliance characteristics at the connection nodes with the structure. Equations of motion for the structure are then written in the frequency domain incorporating the effect of the foundation, the input to the problem being the free-field motion of the structural base. The substructure approach allows a more detailed modelling of the structure, at the same time resulting in a greater flexibility in the selection of the analysis procedure for the foundation and a greater efficiency in numerical computation. The frequency dependent equations of motion for the structure are solved very efficiently by transformation to a generalized coordinate system (Ritz Method) where a few generalized shapes can adequately express the structural response. It is shown that the normal mode shapes of an associated linear system--one that takes the static values of the foundation compliances-serve extremely well as the sought generalized shapes. A computer program is developed to perform the analysis developed and extensive results are presented to demonstrate the effectiveness of the technique.

Available online: http://nisee.berkeley.edu/documents/EERC/EERC-73-09.pdf (7 MB)