Finite-Element Model Updating and Dynamic Responses of Reconstructed Historical Timber Bridges using Ambient Vibration Test Results

Abstract

Historical timber bridges are significant cultural structures and have a long tradition. There are many pre-1950s bridges still in use today. In recent years, great resources have been devoted to the restoration of historical timber bridges to preserve and pass them to the next generations. Because wood is an orthotropic, hygroscopic, and biodegradable material, structural behavior of timber bridges should be evaluated numerically using finite-element (FE) methods before and after restoration and systematic controlled in situ, or nondestructive experimental measurements should be made. This paper considers a historical timber bridge, using numerical modeling and modal testing to determine the structural modal parameters and FE model updating for approximation of numerical results to experimental results. As an application, the Buzlupınar historical timber bridge located in the Çayeli District of Rize, Turkey, is selected. The historical Buzlupınar Bridge was built in the middle of the nineteenth century, restored at different times for different reasons such as fire and wind effects, among others, and restored in 2014–2017. The FE model of Buzlupınar Bridge was formed using commercially available software to detect the initial modal parameters referenced on relief and restoration drawings. The orthotropic material properties are selected according to the laboratory material tests. Results of nondestructive experimental measurements, ambient vibration–based system identification was obtained using the enhanced frequency domain decomposition (EFDD) method (frequency domain) and stochastic subspace identification (SSI) method (time domain). The frequency values and mode shapes obtained by the FE model and experimental measurements are compared. According to these results, six natural frequencies are obtained between 2.0 and 20.0 Hz. Although the mode shapes are compatible with each other, there is a 34.55% difference between the frequency values. In order to reduce the differences, the FE model of the historical timber bridge is updated with a manual update method. Thanks to the model updating, the maximum differences are decreased to below 1% except the fourth mode. To evaluate the influence of FE model update, time-history analyses are applied, and internal forces and displacements are presented.