Civil Engineering Association

Hi All,

I'm looking for sample design calculation notes on the design of pipe arch (elliptical), and arch shaped culverts in both (or) concrete and steel. I've read the previous topics on box culverts and have a solution formed for this type... However, I'm having difficulty analysing the above shapes with regard to soil loads acting on the structure (because of their shape) and the resulting bending moments and shear forces.

Also, I'm using GSA to model these structures and comfirm my calculations. How would you suggest modelling the soil strucure in open arch and pipe arch culverts.

I'm designing to British Standards but any relevant info would be great. I've searched everywhere online!

Thanks

It is better to use FEM analysis. Depending on the shape and the depth you will have either elastic or plastic behavior of the soil. Usually, if the depth is not great and the shape is oval (or like lentil) there will be no tension in the soil and/or plasticity. So you can do it in any FEA program capable of plane strain analysis. Either you will need geotechnical FEA program, like Sigma/w, Phase2, Plaxis, Sage Crisp, Z-Soil, etc. With these you can account for the staged back-filling of the culvert.

If you want to make it old-fashioned, you should account for earth pressure AT REST (not the active or passive one!). It mostly depends on deformation modulus and Poisson ratio. You should be able to do this calculation "by hand" (I mean excel, calculator, mathcad etc.). You will not have such pressure on the "bed" of the structure (that is the ground surface before you construct the culvert). Then on this "bed" you will have only elastic reaction, which depends on the stiffness and the geometry of the culvert. If the culvert is quite simple and smooth shaped, you can take this reaction like linear diagram.

In any case, don't forget the weights: structure, soil above, empty/full water. Most of the big culverts should be tested for sealing by pressurized water before back-filling, especially if they are below an important embankment (let say major road), so you will have this loading also.


Excuse me, but I have never heard about the abbreviation GSA, and I am not familiar with the British practice, but I am sure it should not differ much from the normal world.