Question regarding Box culvert formula in AREMA

[maneesha0702]

I am checking a existing twin cell box culvert for new loads. In AREMA there are formulae given for moment calculations. Moment of inertia of box culvert top slab gross section is equated to Isubscript S. Moment of inertia of box culvert wall gross section is equated to Isubscript W. I am confused as to how to calculate them. Are they about center of gravity of the twin cell culvert or are they about c.g. of the slab and wall repectively. Can somebody shed light on this topic please.

 

[KootK]

Are they about center of gravity of the twin cell culvert or are they about c.g. of the slab and wall repectively.

I vote for the centers of gravity of the slab and wall respectively.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[bridgebuster]

Ditto. Assuming you were going to use moment distribution to perform the analysis - don't laugh - "I" for your stiffness factors would be based on individual elements.

 

[TehMightyEngineer]

I'm almost positive that they're based on the CG of the wall and slab. But I've only done one AREMA box culvert and it wasn't a twin cell. I do a lot more AASHTO box culverts for highways.

Maine Professional and Structural Engineer
American Concrete Industries

http://www.americanconcrete.com

 

[maneesha0702]

Thanks a lot for all the replies. I calculated with c.g. for individual members and the results ( moments and shears as per the formula in AREMA) are in agreement with Structural analysis results.

 

[mike20793]

TehMightEngineer,

A bit off topic, but what program do you use to design AASHTO box culverts? Do you have in house spreadsheets or are you using a program like BRASS Culvert or the TxDOT in house program? Do you ever load rate box culverts?

 

[TehMightyEngineer]

A combination of ET Culvert and in-house spreadsheets with RISA-3D. We load rate all of our box culverts. ET Culvert is nice because it will design both AREMA and AASHTO LRFD culverts.

Maine Professional and Structural Engineer
American Concrete Industries

http://www.americanconcrete.com