# Evaluation of High-Speed Railway Bridges Based on a Nondestructive Monitoring System
## 1 Introduction  
Nowadays, transportation by high-speed trains is considered as one of the important transportation facilities in South Korea as well as in the world's high income countries.Therefore, increasing of the trains' speed is one of the main problems facing existing infrastructure facilities. In Korea, high speed trains started 1992 from Seoul to Busan, while the Korea Train eXpress (KTX) services were launched on 1 April 2004.The bridges and infrastructure of express trains have been developing continuously from 1970. Most high-speed railway bridges are designed based on 350 km/h velocity. Therefore,with the velocity increase, existing bridges should be redesigned and evaluated. The newly-completed train HEMU-430X is currently running at high speed over 400 km/h in the transportation network of Korea. Therefore, this study aims to evaluate the existing composite steel Kaya Bridge of Seoul-Busan High-Speed Railway under the effect of the high speed train movement. The acceleration and strain measurements are used to evaluate the composite bridge under velocities between 290 to 406 km/h. [PERSON] _et al._[1] evaluated steel and pre-stressed concrete (PC) box girder bridgesunder high speed trains up to 289.3 km/h. From their study, they found that no noticeable differences of dynamic responses due to the different materials (steel or concrete) could be found. [PERSON] _et al._[2] evaluated the real observation for the multi-span PC of high-speed railway bridges in a time domain. In their study, they recommended the use of the results as a reference for the design of high-speed railway bridges. [PERSON] _et al._[3] used the long term acceleration measurements to evaluate high-speed railway steel bridges. More monitoring systems for the effect of high-speed railway trains on bridges canbe found in [4; 5; 6; 7]. In general, the main objective of the structural health monitoring (SHM) systems is collecting the observations or information to detect and assess bridge condition, damage, fatigue and performance for proper and timely maintenance intervention. In order to identify the modes of bridge characteristics, it is necessary to excite the structure in order to produce a response at each relevant mode. The loads and response of structures are parameters for the monitoring of the bridge performance under current and future loadings conditions. Typical SHM implementations in highway and steel bridges are summarized in [8; 9]. In addition, for continuous health monitoring studies, the response monitoring technique is more suitable [10]. The evaluation methodologies of high speed railway bridges are concluded in [11; 12; 13]. [PERSON] _et al_. [14] assessed the stress/strain levels, load distributions, and fatigue for four different bridges based on strain measurements, and they concluded that the system is effective in the static performance analysis. [PERSON] _et al_. [15] used asimulation model to evaluate vertical and lateral bridge behavior under high-speed trains. The results of their study showed that the deflections and accelerations of the bridge girder are in accordance with the safety and comfort standards of bridges and running train vehicles. [PERSON] _et al_. [3] proposed the parametric (polynomial fitting) and nonparametric (correlation models, mean value control, root mean square (RMS)) statistical methodology for the acceleration measurements to study the safety and early-warning of the bridge. From their study, they found that the quadratic polynomial fitting provides a good capability for detecting the abnormal changes of the transverse acceleration measurements. Furthermore, the correlation models describing the overall structural behavior of the bridge can be obtained with the support of the health monitoring system, which includes cross-correlation models for accelerations. [PERSON] _et al_. [6] concluded that the numerical simulation gives a good relation between the predicted and the measured responses.