AASHTO Bridge Deck Overhang Design Forces Question for Post and Beam Railing

[Quade999]

Hello,

I'm unsure of how to interpret the design forces for the bridge deck overhang. It says to design for the transverse or vertical forces from the impact table (Design Cases 1 and 2). But it also has a section about calculating the forces based off of the railpost capacity (but it also says you may use those equations, not that you must use them). If the capacity of the rail post is able to resist far more force than the transverse force in the table, than the moment will be huge. Can you just use the forces from the table to design the overhang?
Essentially, what do you do when the force require to fail the railpost is significantly larger than that the force provided in the Table for the Test Level?

Thanks

 

[BridgeSmith]

If the railpost capacity exceeds the moment from the forces in the table, you're allowed to design for the forces and moments resulting from the load in the table. Realize that the post being stronger means if it does get hit, the repairs to the deck may be substantial.

I had to stop and think about that for a minute, because we never use the loads out of the table. By the numbers, our post and rail traffic railing systems don't come close to being adequate. We have our systems crash tested to prove they work.

Also, when they get hit, the failures we see are pretty much exclusively by punching out the back of the curb and the edge of the deck.

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