# Analytical and Measured Effects of Short and Heavy Rail Cars on Railway Bridges in the USA
## 3 Results of Case Studies
### Riveted DPG Spans
#### 3.2.2 Results from Test of DPG Bridge  
Measurements were taken in revenue service and data were collected for loaded coal trains, as well as for other loaded unit trains (grain cars, tank cars) [14]. A total of 10 strain gauges were installed on the girders to evaluate bending stresses: mid-span, 12.2 m (40 ft) from the end, and three cover plate cutoffs (see Figure 4 for more details). In Figure 4, the locations of cover plate terminations are shown for the south girder (G2) and the north girder (G1). Note that the location of cover plate terminations and the overall lengths of each of the two girders are slightly different. The girders are asymmetric because the bridge is located on a curve. Strains due to unit coal trains, unit grain trains, a unit tank train, and several mixed freight trains were recorded. One of the mixed freight trains contained a block of short (12.8-m (42-ft)) cement cars that was also used in the analysis [14]. Figure 20 compares the stress histories for a train with 13.7-m (45-ft) tank cars and a train with 16.2-m (53-ft) coal cars. As predicted by analysis, higher strain ranges were measured at cover plate terminations than at mid-span. The mid-span stress histories showed one large stress range due to a train and very small stress ranges due to individual railcars. Figure 21 illustrates the typical peak stresses caused by unit trains of 12.8-m (42-ft) cement cars, 13.7-m (45-ft) tank cars, 16.2 m (53-ft) coal cars, and unit trains of grain cars on girders G2 and G1. The mid-span location of the south girder experienced bending stresses 26% higher due to short railcars when compared to 16.2-m (53-ft) common length railcars. Stresses at 12.2 m (40 ft) from the end were also more than 10% higher due to shorter railcars. In addition, the 12.8-m (42-ft) and 13.7-m (45-ft) short railcars caused slightly higher stresses at the mid-span location than the 16.2-m (53-ft) coal cars, which were predicted by analytical calculations, as well as measurements on other long spans. The test yielded similar results for the north girder. Compared to 16.2-m (53-ft) coal cars, the shorter railcars produced mid-span bending stresses 22% higher and stresses at 12.2 m (40 ft) from the end 10% higher. The maximum bending stresses at other locations along the span were less prominent. Figure 20: Stress histories obtained from measured strains in south girder G2. Figure 22 compares stress ranges calculated from measured strains at various locations along the span for four types of railcars: 18.3-m (60-ft) grain cars, 16.2-m (53-ft) coal cars, 13.7-m (45-ft) tank cars, and unit trains of 12.8-m (42-ft) cement cars. The highest stress ranges were due to 16.2-m (53-ft) coal cars and 18.3-m (60-ft) grain cars. Based on the span length from center to center of bearings, the span to railcar length ratio was 2.13 for the coal cars and approximately 1.92 for the grain cars. The span to railcar length ratio for the tank cars was about 2.56 and 2.70 for the cement cars. The effect of span to railcar length ratio on service life was discussed in previous publications [19]. Figure 21: Typical peak stress calculated from measured strains—comparison for south girder (top) and north girder (bottom). Figure 22: Stress range calculated from measured strains—comparisons for girder G1 and G2. The span locations that experienced the highest stress ranges are at cover plate terminations, as was predicted analytically and shown on Figure 20. The stress range calculated from measured strains due to 16.2-m (53-ft) coal cars at cover plate 2 termination on girder G2 was about 7.9 MPa (1.15 ksi). This matches the analytical calculation of the stress range of 8.3 MPa (1.2 ksi) (red line, Figure 20). The stress range calculated from measured strains due to 16.2-m (53-ft) coal cars at mid-span of girder G2 was about 0.7 MPa (0.1 ksi). The analytical calculation showed a stress range of 0.5 MPa (0.07 ksi), which essentially matched the actual stress range calculated from measured strains.