SAP2000 result; effect of changing support conditions
SAP2000 result; effect of changing support conditions
(OP)
Hi all, I have been modelling a truss bridge in SAP2000. after modelling and running the analysis i go for the design. but the problem is if I change the support conditions to hinge at left end and roller at right end (both the trusses) from alternately hinged and roller (diagonally same support)the stress ratio at the bottom chord rises from 0.82 to 0.935. And This is happening for vertical load (i.e dead + live). can anybody tell me why is this happening? I have submit the final design within 1 month and I am confused about the arrangement of the supports. Should there be any effect of changing the supports for the design for vertical loads? As Both roller and hinge are capable to resist vertical loads. Please give me some advice.
Regards--
Rafat125
Regards--
Rafat125






RE: SAP2000 result; effect of changing support conditions
Have you include temperature effects in this load case?
I would image the stress in the truss would be higher if you modelled the same fixity conditions at diagonal supports because this is restraining your trusses from any horizontal movement because they are linked by the roadway.
If you model a hinge on the left hand side and roller on the right hand side (the simple beam fixity) for both trusses of your bridge, this effectivley eleviates any built up stresses that result from temperature changes.
RE: SAP2000 result; effect of changing support conditions
No sir I haven't included any temperature load cases. This is a foot over bridge supported at the ends on Elastomers and anchored with stair beams. I have restrained it at the same ends (from horizontal movement) by anchoring it to the beams keeping the other ends free to move (on Elastomers). but this arrangement gives higher stress than restraining it diagonally and keeping other diagonal supports free.
Expecting ur further advice!
Regards--
Rafat125
RE: SAP2000 result; effect of changing support conditions
RE: SAP2000 result; effect of changing support conditions
1) Two trusses
Truss 1: Left-pinned; Right-roller
Truss 2: Left-roller: Right-pinned
2) Rotating the direction of your roller support.
As StructuralEIT indicates, inclining your roller will induce some horizontal restraint.
RE: SAP2000 result; effect of changing support conditions
RE: SAP2000 result; effect of changing support conditions
RE: SAP2000 result; effect of changing support conditions
Ed.R.