Gap NLink element

[jackyyau]

I defined a Gap Nlink with stifness U1=1000kN/m.

In nonlinear analysis, which direction is compression, +'ve local 1 axis or -'ve?

 

[zer]

-ve

 

[Coulomb]

I also need to define a Gap NLlink to model the gap between a shelf and an adjacent wall. How do you determine the stiffness of the gap?

 

[jackyyau]

It depends on the connection details between the shelF and the wall. Without knowing the details, the Gap cannot be defined.

Gap is a compression only spring, and SAP2000 provides an option to allow you to control when it come into functin by defining a real seperation (gap) between the Gap NLink element and the supported Joint. The defined stiffness only come into effect when the deformation exceed the defined seperation.

 

[jackyyau]

Can someone please explain why SAP2000 need to activate Modal analysis (Ritz method) such that nonlinear Gap elements are effective.

Please help!

 

[jackyyau]

In another software SpaceGass, compression-only members uses an iterative analysis method, SPACE GASS puts it into a slightly different category to the other non-linear effects and makes it available in either a linear or a non-linear static analysis.

During the iterations SPACE GASS disables compression-only members which have either end in tension.

It seems this is totally different from SAP2000 which use Modal analysis.

Which method (iterative or Modal) is better?

 

[stressed]

jacky, you only need Ritz vectors if you're doing a time history or other dynamic analysis. SAP does not require you to run a modal analysis unless you're doing dynamic analysis. And with version 9, SAP started offering direct integration time history which does not require modal.