Slenderness in Arches 1

[hyper]

Hi
I've got a problem in the definition. In AASHTO Highway bridges 8.14.3 Concrete Arches says that (lu) is taked as one-half the length of the arch ring. What does lenght really means, is it the span???

Thank you for your help.
Franz

 

[ishvaaag]

No, I think it refers to half the length of the arch along its axis. It maybe relies in the fact of the relevant buckling failure being the antymmetrical one for arches, then being as it laterally fixed at the crown.

In any case for an antymmetrical failure the concurrent moments from the partial vertical load on the bridge must be very relevant and the failure more one on axial force plus notorious flexure than on "buckling".

You can also address the budkling effects well in both planes by merely modeling the bridge with short members, if you want even initial imperfections, and then run elastic plus PDelta analysis. If the members in the model are straight, add then Pdelta for the standing sagitta for each modeled member. You can then dimension directly for the moments so got without any moment amplification, the geometrical nonlinearities are already accounted for, and those material are included in the checking stress block or compatibility of deformations check of each section. If concrete, however, use in the model a much diminished stiffness or modulus of Young (may be that to 28 days divided by 5) to account for loss of stiffness through creep.