General Information
Figure 1 shows a pedestrian truss bridge.
![Steel truss bridge over a highway](bridges/truss-bridges/bridge-4/1-truss-bridge.jpg)
Main span | ≅ 35 m |
Type | Through truss bridge |
Truss material | Steel |
Truss height | ≅ 2.5 m |
Deck width | ≅ 2 m |
Built-Up Section
Figure 2 shows a side view of a truss sector.
![Steel truss of a pedestrian overpass](bridges/truss-bridges/bridge-4/2-truss.jpg)
The upper and bottom chords consist of built-up sections; the diagonals, of square hollow profiles. An upper chord viewed from the front and the side are shown in figures 3 and 4, respectively.
![Front view of a steel composite profile](bridges/truss-bridges/bridge-4/3-upper-chord.jpg)
The built-up section consists of two side-by-side placed H-profiles, an upper plate, and a bottom plate. Upper-and bottom plates are connected to the H-profiles by welding.
![Side view of a steel composite profile](bridges/truss-bridges/bridge-4/4-upper-chord.jpg)
Bridge Drainage
Figure 5 shows a main span sector.
![Bridge entrance region](bridges/truss-bridges/bridge-4/5-bridge-drainage.jpg)
Drainage pipes 1 and 2 are embedded in the abutment cap and abutment. Figure 6 shows the abutment cap, while figure 7 shows the bottom region of the abutment.
![Drainage pipes embedded in the abutment cap](bridges/truss-bridges/bridge-4/6-bridge-drainage.jpg)
![Drainage pipes outlet in the abutment bottom region](bridges/truss-bridges/bridge-4/7-bridge-drainage.jpg)
The thickness of the abutment t ≅ 50 cm, and the diameter of a drainage pipe ≅ 10 cm; the outlets are toward the street side.
What are some possible reasons for embedding the drainage pipes in the abutment cap and abutment?