Geometric nonlinear analysis. Initial deformation

[Nachohp2000]

Dear friends,

I'm trying to model a beam with a initial deformation to perform a geometric nonlinear analysis. I know how to perform the nonlinear analysis but not to introduce the initial deformation. Can anyone help me?

Thanks in advance

 

[stressed]

You've got a couple of options - 1) you could draw the beam (or column) out-of-plumb to begin with or 2) Define load cases as nonlinear and sequence the load cases using the "stiffness at end of nonlinear case" option such that your first load case creates an initial deformation, and the subsequent load case(s) are sequenced to follow after that initial deformation.

There's an automated load pattern option using load pattern type "notional" which applies a user specified percentage of gravity load(s) as a lateral load for purpose of introducing initial deformations or imperfections in the model. Notional loads are required by AISC steel design in the Direct Analysis method.

 

[nachohp]

Thanks, but I need to introduce a initial deformation similar to a buckling mode shape, is it possible? Thanks again

 

[stressed]

As mentioned in my initial reply 1), you would have draw/create the model using the geometry of the mode shape. Not such an easy task, especially if you have a few different shapes. It would be useful if SAP2000 would do this automatically for the user

 

[GipontSap]

Hi.
Another option to model the initial bow deformation it is by introducing a 'strain' load that causes bending in the beam(asign-- frame loads---strain---curvature3axis or curvature2axis....). It should be introduced in a nonlinear load case-1. Then your geometric nonlinear analysis with P Delta (or say,nonlinear load case-2) should start from the end of load case-1.

You can also model the initial bow deformation by introducing a uniform distributed load, causing the same bending...