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Re: Live Load Distribution Factors

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You can always go back to basic statics.  I've designed several bridges where the distribution factors were computed assumeing the deck slab acted at a continous beam over the girders.  The girders were assumed to be simple supports.  The wheel loads were moved to various locations in the lanes to envelope the results.

If you want, you could probably refine the analysis to have the girders provide some fixity to the slab.  I've seen people use a live load generator to do this analysis.  If you e-mail me off the list, I will send you an example hand calculation of the procedure.

--Kipp Martin, P. E. 
Portland, Oregon

>Pat Bachman wrote:

>Greetings from the dry southwest! I am presently designing a >bridge for =
>some unusual live loads as follows:
>~ 80-ft wide bridge to carry two 160-ton coal haulers (Caterpillar >777D).
>~ about 12-ft width between wheels.
>~  two axles spaced at 15-ft.
>~ 105-ft simple span
>~ closely spaced prestressed concrete girders with composite >slab.
>AASHTO LRFD has distribution factors based on span length, >beam stiffness, =
>slab thickness, and beam spacing, but these are developed for >typical =
>highway truck loading.
>Does anyone out there know a reference for distribution of live >loads to =
>the beams? Thanks, Patrick Bachman, P.E.