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Application of IBC 09 Truck/Bus Loading

Application of IBC 09 Truck/Bus Loading

Application of IBC 09 Truck/Bus Loading

(OP)
I am designing a concrete slab supported by concrete grade beams, which in turn, are supported by timber piles. The slab needs to be designed for truck/bus loading (truck/bus repair). I am assuming H20 & HS20. Per Table 1607.6 of the IBC 2009, I must design for uniform load of 640 plf of lane and a concentrated moment design of 18k and a concentrated shear load of 26k. Reading through the commentary and section 1607.6.1, I understand the 640 plf is to be distributed along a 10-foot width; so in my case, the design uniform load is 640 plf/20ft = 64 psf.

I am confused in the application of the concentrated loads in which I can see being analyzed in two ways:

  1. As true concentrated loads: The IBC does not specify if this load is an axle load or load per wheel. Per, 1607.4, the assumed concentrated load area is 2.5ftx2.5ft, which can be assumed for this design. It will make a big difference in the slab design (moment and especially shear) if I divide this load into two separate wheel loads or if I use a single concentrated load of 18k(moment) or 26k(shear). Furthermore, if this is the load per axle, the code does not specify the spacing of the individual wheels (it's 6ft per AASHTO as a guideline). Section 1607.6.1 just states apply one concentrated load for a single span and two concentrated loads in in two spans for a multi-span condition.
  1. As per distributed load per 1607.6.1: This section states, "the concentrated load and uniform load shall be uniformly distributed over a 10-foot width on a line normal to the centerline of the lane placed within a 12-foot-wide lane." To me, this sounds like the concentrated load is divided by 10ft to yield a pounds/ft load. Also, the wording is unclear as to whether or not this line load is applied perpendicular or parallel with the lane direction. Any thoughts? It seems odd to convert a concentrated load into a line load unless this is an attempt to simplify the design?
Does anyone know the correct application of the load per IBC? There should be a loading diagram or it should be clearer. FYI, the design code for my building is IBC, not AASHTO even though IBC developed this section through AASHTO requirements.

RE: Application of IBC 09 Truck/Bus Loading

I've used a bottle jack to jack loaded dump truck wheels for fixing flats. That has a base roughly 10"x12".

RE: Application of IBC 09 Truck/Bus Loading

Here's how I read 1607.6.1:

Both uniform and concentrated loads should be uniformly distributed over a 10 ft. width normal to the centerline of the lane....

So for your uniform load - you are correct, I think, to use 640/10 = 64 psf. This would be across a 10 ft. lane centered in the 12 ft. lane.

For the concentrated load I see it as this:
18000 lbs/10 ft = 1800 plf.
This would be a line load normal to the centerline of the lane and 10 ft. long.

The concentrated load(s) of 1800 plf would be placed anywhere it causes maximum moment.

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RE: Application of IBC 09 Truck/Bus Loading

I don't believe you use the 2.5 ft. square area per the other uniform live loads from Table 1607.1

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