K factor for Arches

[Skicat]

In the AASHTO 4th, there is a table stating that the K factor for arches is no less than 0.7. This is contrary to what we would expect to use (k=0.5) for a fixed-fixed arch, such as the one we have. I'm far from being an AASHTO expert and would like to know if anyone has any experience with arch bridges and could shed some light on the appropriate k factor to use. Thank you.

 

[IDS]

I'm not an AASHTO expert either, but I do design arches on a regular basis.

If we are talking about arches buried in fill here, and if the K factor the ratio of horizontal to vertical soil pressure, then the K value will vary over the height of the arch, and the value will depend on the span to height ratio, the thickness of the arch, and the height of fill, amongst other things. Using a single K value is unlikely to give an accurate result, and often it won't even be in the right ball park.

In my opinion the only reliable method is to do a staged finite element analysis with a Mohr-Coulomb soil model (or something more sophisticated).

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/