Composite beam

Hi,

I am trying to model a composite beam (steel beam + concrete slab).

For this purpose I modeled my composite beam as a steel beam and plate elements.

I applied then an offset distance 0.95 m to the steel beams. Now I see that the steel beam gets a very large axial force and the Mz moment at mid span is very small !!!

If I apply MEMEBER RELEASE (Fx) to the steel beams, the Mz moment would be correct, but what happents if I apply temperature load to the plate elements?

The axial force in the beams will be zero so this approach won't work properly.

I am really confused the way STAAD calculates section forces.

Do you have any clarification on this?

babmou

 

 

Composite Beam.std
Parents
  • Mr.Babmou

    you have released Mx at both ends which in my view should not be done  for any member unless there is some compelling reason for doing so, as the beam would become free to rotate on its axis. That is why you are getting warning messge of instability in your output file.But this is not the reason that you are getting a large amount of axial force in your beam after analysis.You have applied member offset in Y direction to your beam. This is inducing secondary forces in the beam on analysis and is one of the reasons that your are getting axial force in the beam due to gravity loads as well in addition to temperature load. Temperature load is bound to cause axial force if Fx of the member is not restrained. Secondly your concern is that you have released Fixed But Support for Fx but you are still getting Fx in the member after analysis .The reason is that member has got offset  in Y direction but not the support. You are therefore bound to get axial force due to induction of secondary forces unless you relese the ends of beam on the right hand side for Fx or you remove offset from the member.The analysis of beam will be carried out by Staad as per conditions prevailing at the new location, effected after offset.

    I shall be glad to know if any other member of the Forum has a different view in the matter.

    Sureshprsharma

Reply
  • Mr.Babmou

    you have released Mx at both ends which in my view should not be done  for any member unless there is some compelling reason for doing so, as the beam would become free to rotate on its axis. That is why you are getting warning messge of instability in your output file.But this is not the reason that you are getting a large amount of axial force in your beam after analysis.You have applied member offset in Y direction to your beam. This is inducing secondary forces in the beam on analysis and is one of the reasons that your are getting axial force in the beam due to gravity loads as well in addition to temperature load. Temperature load is bound to cause axial force if Fx of the member is not restrained. Secondly your concern is that you have released Fixed But Support for Fx but you are still getting Fx in the member after analysis .The reason is that member has got offset  in Y direction but not the support. You are therefore bound to get axial force due to induction of secondary forces unless you relese the ends of beam on the right hand side for Fx or you remove offset from the member.The analysis of beam will be carried out by Staad as per conditions prevailing at the new location, effected after offset.

    I shall be glad to know if any other member of the Forum has a different view in the matter.

    Sureshprsharma

Children
No Data