SAP2000: Model Ill-Conditioned due to temperature load

[Simba13]

Good Morning all,

I was hoping to get a bit of input/de-bugging on a sap model I'm working on. It's one of a few pedestrian bridges I'm working on for a park. Very simple, HSS stringers, metal grate decking, slight elevation change between the left and right abutment. My issue is that when I run the case for temperature, SAP states that my model is ill-conditioned, it finishes running and there is a huge (relative to applied loads) horizontal force in two of my restraints and I have no idea what that's coming from. My temp range is 60 F. I have a an area/shell section over the surface to apply my area loads. The weird thing is that I have two other models with the same loading conditions but more complex geometry and I'm not having this issue with those.

Any tips?
I'd really appreciate any help.

 

[WARose]

Is there a horizontal release at (at least) one of the supports? If both supports for a beam are horizontally restrained.......you'll have a problem (for a temperature load).

 

[271828]

Two thoughts:

The model is very simple, so do some manual calcs to approximate what the program should be giving.

If Node 5 is released in the Y direction, how far would it move in the Y direction? If that number is very small, then the real structure would probably behave like that release is in place. Thus, use that release in the model.

I have a third thought: Those error messages suck. I've been using SAP2000 a lot for almost 20 years and I have almost never been able to discern from the message what is wrong with the model. When these messages show up, a few times per year for me on average, I typically guess what might be screwing up and fix this or that and the message goes away. Sometimes I can't figure out why it's being displayed and I check the the model and run parallel manual calcs until I convince myself the model is OK, and then ignore the message.

 

[dold]

I agree with these guys. Release node 5 y-direction and see what happens. Thermal forces can be surprisingly large.

 

[STrctPono]

Agreed with everyone else. Your translational restraints should be as follows:

Node 4: Rx, Ry, Rz
Nodes 1 and 5: Rx, Rz

Node 3: Ry, Rz
Nodes 2 and 6: Rz

 

[Simba13]

Hey all!

I really appreciate your help, after looking at your advice and playing with the model a bit more it appears that I was mistaken. The ill-conditioned error wasn't due to the temperature load. I wasn't able to get it to work properly yesterday so I did some hand calcs to get a quick idea of the frequency (the main reason I was using SAP for such a simple bridge was for vibration concerns). So it all worked out, I'll probably play with it a bit more on my own time to figure out why SAP was struggling so much. I really appreciate all of your help though. Thanks!

271828 Yeah SAP can be weird sometimes...