## 2 Field Measurement  
Two direct fixation concrete slab tracks with CWR on a main line of light-rail transit and one ballasted track with rail joints on a vehicle base of light-rail transit were selected as test sections for the field measurements. The dynamic wheel load and dynamic vertical rail displacement applied to the CWR and rail joints were measured during train operation. Section A is a jointed 50 kg/m rail with a ballasted track installed in the vehicle base. The track curvature \(R\) is 60 m and the vehicle speed is approximately under 15 km/h. Figure 2a,b show the cross-sectional and side view of the rail joint on Section A, respectively.  
Section B is a 50 kg/m rail with direct fixation concrete tracks, with a track curvature \(R\) of 300 m and a design vehicle speed of 60 km/h. Section C is a 50 kg/m rail with direct fixation concrete tracks, with a track curvature \(R\) of 100 m and a design vehicle speed of 30 km/h. The tested trains were operated in a two-car formation. The static wheel load of each train when fully occupied is approximately 55 kN.  
The test section and sensor installation locations are shown in Figure 3. The accelerometers were installed at the rail and sleeper, which clearly provide the dynamic responses to impact excitations [16; 17]. Wheel load sensors and displacement transducers were installed on the sleepers or at the centers of the rail support points to measure the dynamic wheel load and vertical rail displacement as each section was subjected to a passing train load. The properties of the test sections are shown in Table 1. For the rail joints, the dynamic wheel load and vertical rail displacement were measured. Vertical rail displacements were measured using displacement transducers such as linear variable differential transformers (LVDTs) mounted on a jig anchored on side bridge inspection passage without influence of train load, as shown in Figure 3. LVDTs (CDP-10M) have sensitivity of \(500\times 10^{-6}\)/mm, a rated power of 6.25 mV/V \(\pm\) 0.3%, and a frequency response of 500 Hz. Displacements are measured and recorded automatically by the computer controlled data acquisition system. The wheel loads acting on the low and high rails of the curved tracks were measured to determine the TIF by evaluating the amplitude and characteristics of the dynamic wheel load during train operation and calculating the dynamic wheel load fluctuation. An example of the measured waveform is shown in Figure 4.  
Figure 2: Schematics of the rail joint. (**a**) Cross section of the rail joint; (**b**) side view of the fishplate of the rail joint (unit: mm).  
\begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Curvature (m)**} & \multicolumn{2}{c}{**Cant (mm)**} & \multicolumn{2}{c}{\(V_{\text{d}}\)} & \multicolumn{2}{c}{\(V_{\text{o}}\)} & \multicolumn{2}{c}{**Track Components**} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} \\ \cline{5-9}  & & & & & **Rail Type** & **Rail Fastener** & **Sleeper Type** & **Ballast** \\ \hline Section A & 60 & 0 & 15 & 15 & 50 kg/m rail joint & E-clip & Wood & Gravel \\ \hline Section B & 300 & 140 & 63 & 60 & 50 kg/m CWR (GPW)[1] & Fast clip[2] & - & - \\ \hline Section C & 100 & 120 & 33 & 30 & 50 kg/m CWR (GPW)[1] & E-clip[3] & - & - \\ \hline \multicolumn{9}{l}{\(V_{\text{d}}\): maximum design speed (km/h), \(V_{\text{o}}\): operational speed (km/h), 1) CVR: continuous welded rail (GPW: gas pressure welded), 2) spring stiffness of rail supporting point: k\({}_{\text{at}}\) = 45 kN/mm (k\({}_{\text{dy}}\) = 68 kN/mm), 3) spring stiffness of rail supporting point: k\({}_{\text{at}}\) = 23 kN/mm (k\({}_{\text{dy}}\) = 29 kN/mm).} \\ \end{tabular}
\end{table}
Table 1: Properties of the test sections.  
Figure 3: Test sections and instrumented sensors. (**a**) Section A; (**b**) section B; and (**c**) section C.