# Evaluation of High-Speed Railway Bridges Based on a Nondestructive Monitoring System
## 4 Summary and Conclusions  
This paper aims to evaluate the measurements of a structural health monitoring system of the Kaya railway bridge in Korea with high-speed trains. A non-destructive monitoring system using accelerometers and strain sensors is designed to monitor the performance of the bridge under new development train speeds of 400 and 406 km/h. The static and dynamic behavior of the bridge are analyzed and discussed. Accordingly, the following remarks and conclusions are drawn:  
* The mathematical correlation models describing the overall structural behavior of the bridge can be obtained with the support of the health monitoring system.
* The torsional response shows a higher effect than the vibration response on the bridge deck.
* The effective torsion test should be assessed at the end points of the bridge.  
Figure 14: Time-frequency acceleration measurements for the trains speeds (a) 290 km/h and (b) 406 km/h.  
Figure 13: Acceleration and strain frequency contents. (**a**) passage-acceleration; (**b**) opposite-acceleration; (**c**) passage-strain; (**d**) opposite-strain.  
The mean value control chart for the acceleration and strain can be applied for bridge monitoring and for the early warning of any abnormal behavior.
* The dynamic factor calculation shows that the static behavior increases with train speed developments.
* The statistical analysis of cubic and quadratic fits shows that the cubic fitting in monitoring strain is better to predict the dynamic behavior of the strain contents.
* The comparison between the results of acceleration and strain dynamic contents shows that the dynamic evaluation of acceleration is better and effective to assess the vibration of the bridge, but the strain dynamic contents can be used to decrease the monitoring cost.
* The fatigue performance of the bridge deck satisfies the requirement of infinite-fatigue-life design method, and the highest cycles occur in a close region of stress mean and amplitude. Therefore, the bridge-deck fatigue is safe under current trains' speeds.
* The frequency calculation of the acceleration and strain measurements shows that the strain measurements are enough to estimate the static and dynamic behaviour frequency domain.
* Comparing the first mode contents of the measurements and the FEM calculations shows that the dynamic behavior of the bridge is safe with development speeds of trains.
* The increase of PSD with train speeds indicates that the simple beam girders of steel bridges are very sensitive to train induced vibrations, and, therefore, may be not suitable for increased speed of train traffic.
* Based on the vibration, torsion, fatigue and frequency contents of the bridge, it is concluded that the bridge is safe under the development speed with a recommendation not to increase the train speed because the torsion performance is critical at 406 km/h at the entrance and exit monitoring points.  
This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, information and communication technology (ICT), and Future Planning (Grant No. 2013R1A2A2A01068174).  
The authors have contributed equally to this work.  
The authors declare no conflict of interest.