MEMBER OFFSET

[Bill2001]

I’m trying to model a small steel bridge construction (3D) in STAAD.Pro.
The structure consists of girders HE500B (main beams) and cross beams HE100B
(secondary beams) which are 120 cm (0.12 m) over CG of girders.
I know that “MEMBER OFFSET” will do the job, but the problem is that I get different results
for Support Reactions (Force Fz) when I apply “MEMBER OFFSET” on girders or cross beams!

I obviously miss out something.
Attached please find a dxf file that shows the cross section of the bridge and also 2 separate input files.
Model-1: ”MEMBER OFFSET” applied on girders.
Model-2: ”MEMBER OFFSET” applied on cross sections.
Which one will be correct?

”MEMBER OFFSET” is the distance between CG of girders and cross beams?
I’ll appreciate if any of you experienced friends could help me out.

Best regards
Bill

 

[edward1]

Bill,
Change all the supports to FIXED BUT FX FZ MX MY MZ KFY 1000. You will get warnings about these but the program adds small stiffnesses and it gives reactions only in Y direction.
Edward1

 

[Bill2001]

Edward1,
Thanks for you quick reply.
In other words, I'm free to aplly memeber offset on either girders or cross beams provided that I change the supports?

Best regards
Bill

 

[edward1]

You will get same reaction. I would model the bracing with offsets from girders. Edward1