## 4 Dynamic Measurements of the Railway Bridge and Crossing Train
### Dynamic Measurements of Crossing Train  
In order to measure the forced vibration responses of the traveling train during the bridge crossing event, a set of 27 accelerometers were installed at different locations of the train (see Figure 17). The sampling rate was chosen at 2400 Hz, and the sensor signals were permanently recorded during train traveling. Before carrying out the measurements on the train, research was undertaken on the appropriate acceleration sensors available on the market. Due to the high acceleration amplitudes expected on the wheelsets and bogies during train traveling, the requirement of a sufficient high measuring range was defined as the first important parameter. Further requirements for the applied sensors were a high resolution of the measurement signals, high sensitivity, an optimal working frequency range, a resonant frequency of the sensor much higher than the frequency range of interest, and a low non-linearity. Based on the defined requirements, the accelerometers of the Integrated Circuit Piezoelectric (ICP) type were evaluated as most appropriate for measuring the train vibrations, and the specifications of the selected sensors are:  
The total length of the considered train is 202 m, and it consists of 11 coaches (\(c1\) to \(c11\)) interconnected through 12 Jacobs bogies (\(b1\) to \(b12\)). The bogies \(b2\) to \(b11\) are regularly spaced at \(s\) = 17.5 m, and bogies \(b1\) and \(b12\) are at a distance of 16.7 m from the corresponding adjacent bogies. Three bogies of the train (\(b2\), \(b6\), and \(b11\)) were selected for instrumentation of uniaxial accelerometers and their installation positions are as follows (exemplarily described for bogie \(b2\)): accelerometers a333 and a334 installed at the car bodies; accelerometers a213, a223, and a224 installed at the bogie frames; accelerometers a113, a114, a123, and a124 installed at the wheelsets. Figure 17: Positions of the installed accelerometers at three bogies of the considered train (a33i installed to the car bodies; a22i installed to the bogie frames; a11i installed to the wheelsets) and picture of accelerometers installed to the wheelset and bogie frame. The train test runs were carried out with four different train speeds (135 km/h, 150 km/h, 160 km/h, and 165 km/h) in both driving directions (Vienna and Salzburg). Every test run was repeated two times in every driving direction, i.e., the total measured train runs were 16. Because only the steel deck bridge with the track in the Salzburg driving direction was dynamically measured by application of forced vibration testing (cf. Section 4.2), the train vibration responses during bridge crossing were just analyzed for the test runs with the Salzburg driving direction. Even though the vibration responses of the crossing vehicle were measured for all considered train speeds and at the location of every installed accelerometer (see Figure 17), a detailed data analysis was carried out for the most relevant (lowest) train speed at 135 km/h (cf. Section 3.2 and note that the resonance speed \(v_{crit,2}=142.4\) km/h is close to the analyzed train speed) and considering the accelerometers installed to the bogie frame \(b2\) and car body \(c1\). These sensors were selected for the evaluation of recorded data in accordance with the conducted numerical simulations to compare the results (see Figure 6 in Section 3.2). Additionally, the analyses of the measurement data identified that the most reliable identification of the bridge's first bending frequency is achieved considering the vibration responses of bogie \(b2\) that enters the bridge as second to last. However, it is planned to analyze the total recorded data within a further research project to investigate the application of further data evaluation methods in the time and frequency domain.