Moment and shear distribution factors for temporary culvert

[foreng]

I have been developing new design standards for simple span temporary log culverts. The life expectancy is less than 2 years. These structures are very common in the forest sector, where a more permanent structure is not required, but the stream crossing must still maintain fish passage. The loads involved are 100 Ton (91,000 kg G.V.W.) with a max design axle load of 204 KN. The culvert structure is similar to a timber culvert in that log stringers are simply supported on a temporary sill and engineered fill is compacted in layers over the culvert to a minimum depth of 0.3 m (1 ft).

Now to the question, I am looking for some guidance on distribution factors for wheel line moment and end shear for this type of structure. Basically the wheel load is spreading vertical influence at some angle through the gravel layer to the stringers, what is it (1:1, 0.5:1)?. I realize the influence will vary depending on the gravel layer depth. A thicker layer will distribute the load to more stringers, to a point, but will increase the dead load.

 

[MichSt]

Have you looked in AASHTO?? I know there is a chapter on the design of timber structures. Also check chapter 6 on Culverts…I believe this is some guidance on the distribution of loads thru fills in that chapter.