Type 1 instability

[SteveG021]

Hi Rafael, 

I have desinged a simple truss walkway but am getting type 1 instabilities in the pin supports in all directions (RX, RY, RZ).

The member utilization ratios are very small, but i cant seem to correct the errors unless i place bracing at the base of the supports.

Is there a solution without over designing the structure?

I have attached the model for your use.

Regards

Steve 

[Rafal.Gaweda]

I think the releases on all columns should be defined as shown below:

[SteveG021]

Hi Rafael,

HOw come you have the Ry fixed for the right sided columns and free for the near side coloumns?
Would this also not create a moment in the pin connection? We are trying to avaoid that.

Thanks
Steve

[Rafal.Gaweda · Accepted solution]

Steve

HOw come you have the Ry fixed for the right sided columns and free for the near side coloumns?

Check results ; releases on beams do that

Would this also not create a moment in the pin connection?

Check results  - see below

[SteveG021]

Hi Rafal, 

I seemed to have solved the problem and was running the analysis error free.

I then made some adjustements to the type of bars< assigning columns, beams and bars, all of which have the same properties.

Please see the attachement to see the latest error. 

Thanks

Steve 

[Rafal.Gaweda · Accepted solution]

Correct defintion of Pinned-Pinned support below: