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Blow Holes
I'm working on a project where we're looking at using a prestressed girder bridge; however, it's in a flood storage area, which submerges the bridge during the 100-year flood. I'm looking for guidance on using blow holes in the top of the deck to allow the air between the girders to escape, which will alleviate buoyancy and girder lateral loading problems. What do you think?
If this is a new bridge, we do not allow the PCB low member elevation to be set below the overtopping tailwater elevation. You should first consider raising the grade. If the observed high water is recorded to be above the design low member elevation per above (rarely the case), then the following should be implemented:
- Provide vent holes at quarter points along all beam webs
- Vent holes should be located at the top of the beam web
- Vent holes should be 2 inches in diameter, achieved with a PVC pipe
- Show vent holes on PCB detail sheets, on section at centerline span
- Show vent holes in a schematic beam elevation, holes at 1/4 points
Note: blow holes are not required on multiple span PCB bridges with open beam diaphragms over the piers.