# Fatigue Performance Test and Numerical Analysis of Composite Girders with CSW-CFST Truss Chords
## 2 Model Test  
### Model Design  
It has been found [8] that the dead load of a girder can increase by 8% because of concrete-filling the chord, while the bearing capacity can increase by 22%. Concrete-filling the chord can enhance the radial stiffness of the chord, which can reduce the thickness of the chord. Concrete-filling the chord involves more labor, more material consumption, higher  
Figure 1: Composite girders: (**a**) CSW-CFST chords; and (**b**) CSW-CFST truss chords. Figure 2: Photo of completed bridges: (**a**) a footbridge in Hebei Province, China; and (**b**) Maluanshan Park Viaduct in Guangdong Province, China. self-weight, and added uncertainties, but the advantages outweigh the disadvantages described above. To analyze the influence of concrete-filling the chord on the fatigue performance of composite girders with CSW-ST truss chords, the model designed for this study adopted the same geometry and materials as composite girders with CSW-ST truss chords investigated in [11], except that the chord was filled with concrete. The scale of the test model was 1:5. Figure 3 shows the detailed dimensions. The total length and span between the supports of the test model were 9000 mm and 8760 mm, respectively. The height of the end cross beam and main girder cross-section were 600 mm and 560 mm, respectively. The width and thickness of the concrete bridge deck slab were 1700 mm and 100 mm, respectively. The steel grade used in the fatigue performance test was Grade Q345 steel [17]. These welds comprised full penetration welds, with the material properties of the welds needing to be consistent with the steel. The size of the welds was determined by reference to stipulations given in [17]. The detailed specifications of the chord, corrugated steel web, horizontal bracing, cross-bracing, and K-bracing are listed in Table 1. According to [18], the main geometric parameters of the corrugated steel web include the dip angle of the inclined web (\(\theta_{\text{w}}\)), and the bend radius (\(R_{\text{w}}\)), thickness (\(T_{\text{w}}\)), wavelength (\(L_{\text{w}}\)), and wave height (\(H_{\text{w}}\)), as shown in Figure 4; the detailed dimensions of the corrugated steel web are shown in Table 1. The intersecting location of the inclined web and the arc transition segment is represented as point S. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Chord**} & \multirow{2}{*}{**K-Bracing**} & \multirow{2}{*}{**Horizontal Bracing**} & \multirow{2}{*}{**Cross-Bracing**} & \multicolumn{4}{c}{**Corrugated Steel Web**} \\ \cline{5-8}  & & & & \(T_{\text{W}}\) & \(\theta_{\text{W}}\) & \(L_{\text{W}}\) & \(H_{\text{W}}\) & \(R_{\text{W}}\) \\ \hline \(\mathcal{O}\)146 mm \(\times\) 6 mm & L23 mm \(\times\) 4 mm & L5 mm & L40 mm \(\times\) 3 mm & 4 mm & 31\({}^{\circ}\) & 320 mm & 44 mm & 60 mm \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of test model specifications. Figure 3: Scaled test model and layout of measurement points (unit: mm): (a) elevation; and (b) cross-section. To facilitate analysis and exposition, the two sides of the intersecting weld between the corrugated steel web and the chord are referred to as the left- and right-hand-side, respectively, with the axial direction of chords understood as the forward direction according to the path direction of the corrugated steel web. The corrugated steel web was further divided into the mold-pressing side (indicate in red in Figure 5) and the non-mold pressing side (indicated in blue in Figure 5) with respect to the position of the fixed molding head. The mechanical properties of the steel and concrete used in the test model were determined from experimental stress-strain curves. As shown in Tables 2 and 3,\(f_{y}\),\(f_{u}\), \(E_{8}\) and \(u_{s}\) represent the yield strength, ultimate strength, modulus of elasticity and Poisson ratio of the steel structure, respectively.