Finite Element Model Updating for a Cable-Stayed Bridge Using Manual Tuning and Sensitivity-Based Optimization

A model updating procedure for developing a finite element model for the Seohae Bridge is proposed. The bridge is a slab-on-stringer cable-stayed bridge with a main span of 470 m and has been in operation since 2000. Natural frequencies and mode shapes identified from ambient vibration measurements with the dense application of 80 accelerometers were used as target values in developing the model. The procedure consists of two consecutive steps. The first step is to establish a baseline model using a manual tuning method, which utilizes construction and maintenance history as well as the initial design information. Variations in natural frequencies due to temperature changes are also considered in the manual tuning with the help of long-term monitoring data regarding natural frequencies and temperature. Although the manual tuning was done efficiently, errors between the analysis and measurement of the dominant natural frequencies are estimated to be 5-12%. In the second step, the baseline model is calibrated by an automated model updating procedure. Sensitivity-based optimization is used to construct the final model, in which the updating parameters are selected on the basis of a preliminary sensitivity check. In order to obtain physically meaningful solutions, the changes in the updating parameters are also minimized by including them in the objective function in the form of penalty function. The optimization procedure results in a finely tuned model that shows the maximum differences in natural frequencies to be less than 3% for the lowest two modes and 6% for the other modes. The changes ill the updating parameters still remain within the allowable ranges of 5-15% specified for each parameter, based on an engineering judgement.