Model Expansion Joints In RISA 3D

[JoshH726]

Is there a standard protocol to model expansion joints in a steel frame? Springs? Separate structures? I am modeling a long steel cantilever frame (8' cantilever, 350' long). When considering temperature effects, i would like to allow the frame to breathe, but not sure the best way to incorporate expansion in the frame. Any thoughts, comments, suggestions would be appreciated.

 

[JoshPlumSE]

JHost -

I'm not sure that I fully understand your structure or intent. But, I have some thought on the subject of expansion joints and thermal expansion:

1) Thermal expansion is a self limiting effect. By that I mean that the amount of stress that develops will be very limited if the structure is allowed to expand. If you try to rigidly restrain it, then the stresses can be very large.

2) I've worked on some types of structures where we allowed thermal expansion by using long or short slotted bolt holes. In RISA this would be modeled by using the member end releases to dictate that no force can be transferred in the direction of the slot.

3) I've seen other cases where thermal restraint forces get dramatically over estimated near support locations. This was because the boundary conditions are modeled as infinitely rigid. In those cases, I might replace the rigid boundary condition with a relatively rigid support spring. Let's say the stiffness of the spring is 10,000 kips per inch of deflection. That would still be a pretty rigid support. But, it may allow enough movement that the thermal stresses would not be allowed to develop. Obviously, you want to make sure that you use a reasonable value for your springs. Something that is going to be closer to reality than the infinitely rigid assumption.