Direct Updating Method for Structural Models Based on Orthogonality Constraints

Abstract

Discrepancies always exist between the dynamic properties predicted by a finite element model and those measured directly from the structure. In this study, a direct method based on the orthogonality constraints is proposed for updating the mass and stiffness matrices of the structure first using a single set of modal data. This method hinges on replacement of the modal vector of concern by the modal matrix in computing the correction matrices to solve the problem of insufficient known conditions. Such a method is then extended and applied in a consecutive manner to update the structural model for each of the first few modes that are experimentally made available. In the numerical studies, it was demonstrated that for buildings of the shear type, the natural frequencies predicted by the updated model agree well with the measured ones for those modes that are experimentally made available, while the rest modes remain basically untouched. The approach proposed herein is simple, accurate and robust, which should be favored by engineers for practical applications.

Keywords:

• direct updating method
• mass matrix
• model updating
• shear building
• stiffness matrix
• structural modeling

ACKNOWLEDGEMENTS

The research presented herein is sponsored in part by the National Science Council through Grant No.: NSC 93-2211-E-002-046.