AASHTO LRFD "At-Grade" Box Culvert Loading

[TypeIV]

I am designing an "at grade" (Cover < 2'-0") RCB using AASHTO LRFD.

The State DOT I am in specifically requires us to use LRFD for RCB's. The LRFD Code only requires the full analysis for HL93 and Lane Load if the supporting walls are > 15 feet apart. I am designing a Triple 10'(W)x6'(H) reinforced concrete box and the code says "Where primary strips are transverse and their span does not exceed 15.0 ft.-the transverse strips shall be designed for the wheels of the 32.0-kip axle."

I am trying to understand how to apply this load, as stated above.

I have a three barrell box and I am wondering if that 32 kip load is acting alone and moved across the three spans for maximum forces or is it multiple 32 kip loads at some (14'?) spacing moved across the three cell spans?

[I would also be interested in any software that anyone has had success with.]

Thank you

 

[jimaitken]

The HS-20 axle load configuration is 32k-32k-8k at 14 ft min spacing. I would probably use all three axles (assume 14 ft spacing) with a 32 kip load on the slab over two barrels and an 8 kip load somewhere on the third barrel, and run a few cases to maximize the loads. This will take advantage of the continuity to reduce the maximum + moments , and determine the - moment over the barrel walls.

...or use a program like STAAD, RISA or GT STRUDL and run the moving load generator on a stick model to get all the live load posibilities. Apply the results to your design.

 

[TypeIV]

Thanks jimaitken!

I think I will do that and do the same for the OK overload truck too.

Happy New Year!

 

[Andy10]

BRASS CULVERT LRFD is a good program to design Box culverts to the AASHTO LRFD code (3rd edition with 2006 interims). See

http://www.dot.state.wy.us/generic/brass/

STAAD.Pro is the other way to go but takes much longer.

We us Brass to design the box (with hand checks to verify) and design the headwalls independantly.

Something to consider.

 

[TypeIV]

Thank you Andy10, I will look into that.