Water Load on Beam when Q100 elevation is above the low beam point 1

[Dwaipayan Sharma]

Hi,

I have been trying to calculate the water load on beam when Q 100 is above the low beam point. I have following question:

1. How do we calculate the pressure on beam due to water?
2. How do we check the adequacy of beam with respect to water load?
3. When do we need to provide the diaphragm if the beam is not adequate and it's design?

Thanks in Advance!

 

[BridgeSmith]

1) I don't have access to my AASHTO spec right now, but the applicable equation is in the water loads section (3.7, I believe)
2) Apply the load as a lateral line load on the bottom flange. Check the bending stress in the bottom flange using its Sy and modeling the bottom flange as a continuous beam with the diaphragms as support points. Combine the stress from the water load with the stresses from the dead and live loads according to the applicable load combinations, and the combined stress equations. Again, I don't have access to the spec right now, so I don't know the equation numbers, but I believe the applicable equations combine the stress from vertical loads with 1/3 of the stress from lateral loads.

3) If it fails a combined stress check, the spacing of the diaphragms will need to be decreased until it does pass.

You'll need to provide restraint for the lateral forces on the bearings. Also, be sure to account for buoyancy loads that could lift the superstructure off its bearings, either by providing vent holes in the girders, or by restraining the girders.

Rod Smith, P.E., The artist formerly known as HotRod10