CIP box culvert skewed to traffic

[damorim]

Hello everyone,

I'm working on a single cell 6m wide by 3m tall (clear dimensions) cast-in-place concrete box culvert. The CL of the culvert is skewed to traffic (approximately 33 degrees). I just want to confirm the procedure to analyze this culvert before I get too far in... I'm thinking that I should still analyze this as a 2D frame using the 1m equivalent strip method. The frame would be drawn with the dimensions perpendicular to the CL of the culvert (ie. span of 6m, NOT the parallel to traffic dimension of almost 8m). Also, main reinforcing will still be perpendicular to the culvert CL. Additionally, as per AASHTO LRFD 12.11.2.4, wheel distribution loads need not be corrected for skew effects.

Anything I'm missing or reasons the above would be incorrect?? The way I see it, load on the box top slab will still travel to the walls perpendicular to the culvert CL, so not accounting for the skew should be ok.

 

[JStructsteel]

wouldn't your shear jump up on the shorter end?

 

[NickBing]

If the box culvert is rectangular in plan view, and is simply oriented at an angle compared to the direction of traffic, then I agree that the span is 6m. However, if the ends of the box culvert are skewed to match the traffic direction, then the design span at those skewed ends would need to be greater than 6m, and as jrisbo mentions, shear would need to be looked at.

 

[damorim]

So since this box is in the order of 40m long, I will design it as if it is rectangular in plan view (typical section) and then deal with the corner effects separately as the ends are skewed to be parallel to traffic. Anyone have examples or good information for dealing with those corners?

 

[NickBing]

Here's an example of how we treat the end skewed section of a precast box culvert. I realize you are dealing with CIP, but the concept is the same. We use a 4'-0" design beam width, and a span length equal to the skewed length. Reinforcing is "fanned out" from the short side and placed so that the required area of steel is met at mid span. The bar clearances that you see here may be less that what you could use for CIP.

 

[damorim]

Thanks NickBing

 

[robyengIT]

in U.S.A. for culvert design You can use (free download)the software called "CANDE" that is Culvert analysis and design