# Development and Testing of a Railway Bridge Weigh-in-Motion System
## 3 RB-WIM Installation and Testing  
A single-track truss bridge in Poland was selected for testing of the RB-WIM system (Figure 4). The bridge is located in Nieporet, near Warsaw. Constructed in the 1970s, it is one of over one thousand similar bridges in Poland [37]. It spans 40 m and consists of five 8 m long days. The bridge has deteriorated significantly since first constructed. As a result, it does not carry heavy traffic load and the velocity of the crossing trains is limited to 20 km/h (considerably lower than the average train speed of 160 km/h in Poland) [38]. The speed restriction at the test bridge may raise a concern regarding the applicability of the study for higher traveling speeds. However, previous studies in road and railway B-WIM [26] have shown that there is no obvious correlation between accuracy and the speed of the vehicle. The application of the B-WIM system in weighting vehicles at full highway speed (checked against static weights) is demonstrated in several studies [25; 39]. Figure 4: Nieporet Bridge: (**a**) elevation and (**b**) view from underneath. Figure 3: Influence line for the Nieporet Bridge. The bridge is supported on four steel bearings, illustrated in Figure 5, two at each end. It carries a single unballasted railway track that runs along the centre. The structure of the bridge consists of two main vertical trusses, one at either side. The trusses are connected along the bottom by six cross beams that are located at the node points of the bottom chord. The railway track is supported by timber sleepers that span onto two \"stringer\" beams. These stringer beams extend longitudinally and are supported by the six cross beams. The loading on the track is transferred onto the sleepers and then onto the stringer beams. The stringer beams transfer the load into the cross beams, which are supported at the node points of the trusses. The Nieporet Bridge has been studied since mid-2007 due to interest from Polish Railways in the development of structural health monitoring (SHM) systems for railway bridges [40]. The bridge has been instrumented with a number of sensors, data from which are in the literature [40]. Prior to installation of the RB-WIM system, some of these published results were used to confirm the accuracy of the static model. For this purpose, a finite element model of the bridge was created using the Midas finite element software package. The bridge was modelled using beam elements, with full fixity assumed at node points. The design drawings were used to calculate cross sectional properties. A Young's Modulus of \(E=210\times 10^{6}\) kN/m\({}^{2}\) was assumed throughout [41]. Figure 6 shows the MIDAS model of the bridge, identifying some of the main structural elements. The rail and sleepers have been omitted for clarity. The numerical model of the bridge was validated at a number of important measurement locations using recordings from a previous measurement campaign [40]. Having established a good match between the response of the model and the measurements collected by [PERSON] et al. [40], it was used to develop the instrumentation strategy for the in-field testing of the RB-WIM concept. Figure 5: Nieporet Bridge bearing (**a**). edge and (**b**). view from underneath bridge. Figure 6: MIDAS model of Nieporet Bridge [41]. Strain transducers were installed on the longitudinal trusses, on the stringers, and on the cross beams to provide full coverage in the central part of the truss. Sensors were also located on one stringer beam in the bays on either side of the centre (i.e., sensors 1 and 8 shown in Figure 7). The locations of the sensors are marked with grey squares in Figure 7. The numbers represent the data acquisition channels. To avoid welding or drilling, steel mounting plates were used as interfaces. They were bonded to the structure with epoxy and, after hardening, the strain sensors were fastened with nuts. Additionally, strain gauges were bonded directly to the bridge at locations 3 through 6.