ASSHTO Bridge Wheel Load Distribution for Permit Vehicle

[SteveGregory]

For an HS truck, the wheel spacing is 6 feet and there are specific rules for the load distribution to the exterior and interior girders.

Maybe, I haven't looked hard enough in our ASSHTO specifications for the answer. I have a crane vehicle that needs to cross a short simple-span bridge. The crane has 6 axles and different wheel spacings for the front 3 axles and the rear 3 axles. Should I use the actual wheel spacing and calculate the load distribution in a direct proportional manner or should I use a 6-foot spacing with the appropriate ASSHTO rules.

 

[redtide]

Steve...looking at the 2011 Manual for Bridge Evaluation by AASHTO under Special Permit loads section 6A.4.5.4.1 it states that "The Loading for evaluation of special permits shall be the actual permit truck, axle loading, configuration, weight and distribution of load to the axle." In addition, it states that a particular live load factor must be applied when evaluating (varies with several different physical circumstances) and that the bridge must have a confirmed RF (Rating Factor) greater than or equal to 1.0, prior to using this evaluation procedure. "Special permits" are defined as usually of a one way single trip...hope this helps.

 

[SteveGregory]

Redtide,
This bridge is privately owned by an industrial plant. I was using an older ASSHTO (16th Ed.1996) manual for this job. I was using the Load Factor Design method rather than ASD or LRFD. There is a more experienced fellow here that is helping me. The load factors are a little baffling to me.