It appears to me that heavy vehicle garage demands in IBC 2012/2015 are substantially higher than IBC 2009.
Beginning with IBC 2012, section 1607.7.3 Heavy Vehicle Garages references "the jurisdiction having authority", which is typically AASHTO with local amendments. IBC 2009 had Table 1607.6, which was a lane load plus a single concentrated load, and this is gone from the more recent editions. If I go back to the old AASHTO ASD that was source material for IBC, it contains two methods: Method 1 - identical to IBC. Method 2 - axle loads of 8k + 32k + 32k without any lane load. For a typical garage bay span, method 2 is going to govern. Old AASHTO has an appendix in the back that provides moments and shears as a function of span, and method 1 (used in IBC) only governs at spans over 150! It seems to me that by omitting the 3 axle procedure, the provisions provided by IBC 2009 are extremely unconservative.
With the latest codes, we are required to use the current AASHTO code without the dynamic load allowance, which includes multiple lane occupancy factors and higher load factors for strength combinations. More importantly, it does not contain the uniform load plus single point load procedure. The end effect being we are using the same 640 plf as before, but instead of a single 18 kip load, we are using 3 axles of 32k, 32k, and 8k.
Am I missing something here, or does this result in much much larger design demands?
I guess we can lean on the IBC Exception in section 1707.7.3, which for heavy vehicle (i.e. bus) garages states you can use the actual vehicle weights combined with a rational analysis instead of the AASHTO axle loads. Google tells me the max axle weight of a bus is 20.5 kips.
I'd appreciate posts from engineers proficient in both IBC and AASHTO, or engineers with experience design bus garages.
Thanks!
Beginning with IBC 2012, section 1607.7.3 Heavy Vehicle Garages references "the jurisdiction having authority", which is typically AASHTO with local amendments. IBC 2009 had Table 1607.6, which was a lane load plus a single concentrated load, and this is gone from the more recent editions. If I go back to the old AASHTO ASD that was source material for IBC, it contains two methods: Method 1 - identical to IBC. Method 2 - axle loads of 8k + 32k + 32k without any lane load. For a typical garage bay span, method 2 is going to govern. Old AASHTO has an appendix in the back that provides moments and shears as a function of span, and method 1 (used in IBC) only governs at spans over 150! It seems to me that by omitting the 3 axle procedure, the provisions provided by IBC 2009 are extremely unconservative.
With the latest codes, we are required to use the current AASHTO code without the dynamic load allowance, which includes multiple lane occupancy factors and higher load factors for strength combinations. More importantly, it does not contain the uniform load plus single point load procedure. The end effect being we are using the same 640 plf as before, but instead of a single 18 kip load, we are using 3 axles of 32k, 32k, and 8k.
Am I missing something here, or does this result in much much larger design demands?
I guess we can lean on the IBC Exception in section 1707.7.3, which for heavy vehicle (i.e. bus) garages states you can use the actual vehicle weights combined with a rational analysis instead of the AASHTO axle loads. Google tells me the max axle weight of a bus is 20.5 kips.
I'd appreciate posts from engineers proficient in both IBC and AASHTO, or engineers with experience design bus garages.
Thanks!
