bridge load capacity

[cvg]

I am trying to evaluate a bridge for temporary construction loadings. Loading will include concrete trucks, small heavy equipment, light duty crane, etc.

plans indicate AASHO 1953 Loading Class H15-S12-1944

bridge inventory indicates
operating rating of 40 tons
inventory rating of 23 tons
Sufficiency Rating is 87.3

I am trying to determine what the AASHO criteria was

 

[BridgeSmith]

Well, I think I can get you part way there. The H15 truck has a 6 kip front axle and a 24 kip rear axle and they are 14' apart. Wheel line gauge is the same 6' as any other design truck. According to the table we use for rating those older bridges, for that era steel yield strength is assumed to be 33ksi, allowable for Inventory level is 18ksi, and allowable for Operating was 24.5ksi.

Honestly though, I think the better way to go about it for construction loads, some of which don't conform to the 6' standard gauge, is to just do a load rating for the loads to be applied. Calculate the capacity of each girder, based on its section modulus and bracing condition, calculate the Load Fraction (the portion of the weight of the equipment to an individual girder), apply it, along with the dead load, to the girder of interest, and see how it rates.

 

[BridgeSmith]

Btw, the rating equation is: Live Load / (Capacity - Dead Load)

 

[ukbridge]

As a ballpark figure, we typically allow for 1.5kPa which allows for the additional weight of wet concrete, plant, light cranage etc.