Wheel Load Distribution

[lsmfse]

I am designing a concrete top for a roadway box. The span is 6'. I am designing the slab based on a 1'-0" strip. Based on my research, AASHTO(1992 edition) gives a distribution width of 4+.06S.(Reinforcement paralell to traffic) This gives 4.36', therefore, I assume that for a 16k wheel load, I would have 16/4.36 or 3.67k/ft(not including impact)and a moment of 3.67x6/4= 5.51 ft-k. In the same section, moments may be approximated as 900S which in my case would = 5.4 ft-k. Could someone confirm my interpetation? I remember years ago my superiors would use a number of 12"+2x slab thickness(something like this)for concentrated loads on floors. If I applied this "rule of thumb", my moment is on the order of 11.08 ft-k, almost double.
Thanks

 

[miecz]

Yes, that is the correct distribution of a wheel load on a highway slab with the reinforcement parallel to traffic. To my knowledge, there's no universally accepted distribution for building slabs, so you'll see various rules of thumb, some more conservative than others. Keep in mind that AASHTO requires you to factor your loads by [γ], [β], and add impact.

 

[Umassengr]

Is the top of slab also the riding surface or is there a roadway pavement and fill over the slab? If the slab is buried use AASHTO Standard Specs Section 6 "Culverts" for the LL distribution through fills (D>=2 ft)

 

[lsmfse]

meicz, thanks for the confirmation. I included 30% impact.
Umassengr, there will be 1 1/2" asphalt topping over the concrete.