# Dynamic Performance of a New-Type PSC I-girder for Railway Bridge Application
## 2 Dynamic Performance Evaluation of New Type of PSC I-girder Bridge
### Performance Evaluation by Moving Load Analysis  
#### 2.2.1 Performance Evaluation Criteria  
Compared to the road bridge, the railway bridge experiences larger live loads and may suffer dynamic problems like resonance due to the cyclic loading generated by the train wheels traveling at high speed. The railway bridge must thus satisfy thorough vibration limits as well as vertical deflection limits. Accordingly, the railway design code (KDS 24 10 10) requires to perform moving load analysis for the train load per range of traveling speed and to perform the evaluation of vertical acceleration, vertical deflection and twist of the bridge span in order to secure the dynamic stability of the railway bridge subjected to traveling trains. Table 3 details the limits for each check item specified in KDS 24 10 10 [11]. \begin{table}
\begin{tabular}{c c c c c} \hline
**Item** & **Application** & **Limit** \\ \hline \multirow{2}{*}{Vertical acceleration} & \multicolumn{2}{c}{Gravel ballast track} & 0.35 g \\  & \multicolumn{2}{c}{Concrete ballast track} & 0.5 g \\ \hline \multirow{3}{*}{Twist} & Standard train load & \(V\leq\) 200 km/h & 3.0 mm/3 m \\  & \multicolumn{2}{c}{Dynamic analysis with real train} & 1.5 mm/3 m \\ \hline \multirow{3}{*}{Vertical deflection} & \multirow{3}{*}{Span length} & \multirow{3}{*}{30 m} & \(L/1600\) (270 \(<V\leq\) 350) \\  & & & \(L/1500\) (200 \(<V\leq\) 270) \\  & & & \(L/1300\) (\(V\leq\) 200) \\ \cline{3-5}  & & & \(L/1750\) (270 \(<V\leq\) 350) \\  & & & \(L/1600\) (200 \(<V\leq\) 270) \\  & & & \(L/1500\) (\(V\leq\) 200) \\ \cline{3-5}  & & & \(L/1900\) (270 \(<V\leq\) 350) \\  & & & \(L/1700\) (200 \(<V\leq\) 270) \\  & & & \(L/1500\) (\(V\leq\) 200) \\ \cline{3-5}  & & & \(L/2100\) (270 \(<V\leq\) 350) \\  & & & \(L/1900\) (200 \(<V\leq\) 350) \\  & & & \(L/1700\) (200 \(<V\leq\) 270) \\  & & & \(L/1500\) (\(V\leq\) 200) \\ \hline \multirow{3}{*}{Vertical deflection} & \multirow{3}{*}{Span length} & \multirow{3}{*}{35 m} & \(L/2100\) (270 \(<V\leq\) 350) \\  & & & \(L/1900\) (200 \(<V\leq\) 270) \\ \cline{3-5}  & & & \(L/1400\) (\(V\leq\) 200) \\ \hline \end{tabular}
\end{table} 
Table 3: Railway bridge specifications for traveling safety and comfort (KSD 24 10 10) [11]. Figure 4: Front view of railway bridge section: (**a**) application of 4 girders for span lengths of 30 m and 35 m; (**b**) application of 5 girders for span lengths of 40 m and 45 m.  
The five different train loads listed in Table 4 were considered in the moving load analysis. These train loads correspond to those currently in operation or under plan. Here, the Saemaeul train and the freight train are conventional trains operating in the previous railway network and KTX (Korea Train eXpress) stands for the high-speed train. HEMU (Highspeed Electric Multiple Unit) and EMU (Electric Multiple Unit) are the high-speed trains of the next generation. Table 4 provides also the composition of the convoy, the size of the axle load and the effective beating interval for each of the considered trains. Figure 5 shows the KTX train, one of the five train models. Moving load analysis was performed at intervals of time until the train started from the point of the bridge and completely passed the bridge. At this time, the element was set to hit three or more times to ensure numerical stability. The occurrence of resonance or resonance suppression in the railway bridge depends on the relationship existing between the effective beating interval and the span length [12; 13; 14]. Resonance occurs when the natural frequency of the bridge coincides with the frequency of the force vibration generated by the periodic beating of the regularly spaced axles of the train.