System identification work on 199+325 steel railroad bridge and development of its calibrated finite element model

Railroad bridges maintained and operated by the State Raid Road Agency (TCDD) constitute the main passage ways and junction points of the railroad network of the country. Most of these bridges have been under service for more than 100 years. These bridges are exposed to larger service loads as compared to the highway bridges, and are open to external actions leading to changes in their dynamic parameters. Due to these reasons, the railroad bridges must routinely be checked and serviced. The routine checks done by TCDD are based on visual inspection, and highly subjective and dependent on the technician's experience. This increases the chance of making mistakes and missing hidden structural damages. Vibration-based structural health monitoring offers a more objective framework which has the potential to reduce operator dependent nature of the routine checks. This study presents modal parameter estimation studies by in-situ experiments and a developed reference numerical model of the 199+325 steel railway bridge located in Usak. The dynamic response of the bridge was measured in four different test setups and in two different temperature states, and under ambient vibration conditions. Modal parameters of the bridge are estimated using two different output-only system identification methods, namely, Enhanced Frequency Domain Decomposition and Data-driven Stochastic Subspace Identification methods. The identification results obtained under different temperature conditions are compared in assessing the effects of temperature change in identification results. Three dimensional finite element model of the bridge is created using FEDEASLab software. Trial-and-error type model updating study is conducted. Therefore a reference numerical model of the bridge representing its current condition is obtained. This model will be facilitated in the future for damage identification purpose using the sensitivity based finite element modeling updating method