Buckling Analysis 1

[slickdeals]

Folks,
Has anyone done a buckling analysis on a truss in SAP2000? I am trying to use this to calculate buckling load on a column and back track to calculate effective length to use in design.

 

[IJR]

Slick

that can be done. But what you get in Sap2000 is elastic buckling. You are actually determining Pcr, not design buckling resistance

That is not bad, gives you a great idea, since design buckling resistances are somehow related to Pcr.

Create an analysis case. In the analysis type use Buckling from the pulldown list, then add load cases for which you would like to find Pcr. These are added in the ratio you specify. It is usual to use gravity loads alone.

When you run the analysis and ask for deformed shape under your buckling analyis, SAP2000 will give you a factor. When this is less than zero, then the loads you have specified exceed the loads that would give Pcr for your system.

I use this option only to get a feel and warning as to where I need to put more bracing or provide more resistance.

But these results have no direct relation to design buckling resistances and you will have trouble defending your design to authorities


respects
ijr

 

[stressed]

You may also consider modeling your column with a kink, or applying a small lateral load to it before running the buckling analysis. Because otherwise SAP2000 will assume a perfectly symetrical structure for calculation of buckling load, and calculate a higher buckling load than is reality.

SAP2000 also calculates nonlinear snap through buckling, but you don't do this by adding a buckling case. You add a static case with nonlinear P-delta with large displacements. Alternatively you can run the large deformation as a direct integration time history and step through it.