Finite element model updating of a highway bridge based on operational modal analysis

This paper deals with the dynamic identification and finite element model updating of Magaz bridge, located in Spain. It is a three span continuous bridge with composite steel-concrete cross section. Operational modal analysis was performed from ambient vibration data by the covariance driven stochastic subspace identification algorithm. A very accurate three-dimensional finite element model was built using SAP2000 assuming geometrical and mechanical properties from the original drawings. At the first step of the calibration process, a parametric study was performed to identify the most sensitive parameters affecting the finite element model-computed modal frequencies and mode shapes. The automated finite element model updating problem has then been formulated as an optimization problem. The uncertainty on some physical parameters has been adjusted through an iterative process that aims at minimizing the objective function, hence to solve a nonlinear least squares problem which has as its subject the residuals of the relative difference from the numerical and experimental eigenfrequencies and eigenvectors. The outcome of the optimization is a significantly improved finite element model with very good agreement in terms of frequencies and modal assurance criteria values on the first modes.