RISA 3D analysis

[fish1]

Hello,
I am hoping someone can help me out with a truss analysis I did using RISA 3-d. I have not used RISA in a few years, and i have designed a wooden truss for a friend building a house. I decided to check my hand calcs with RISA to get more familar with the program. I set up the model nodes and defined all the members, and the results i am getting are not making sense. After inspecting the moment diagrams i have determined RISA is not recognizing some intermediate connections and supports of some of the members. It is also stating that some of the Nodes are "locked". I suspect i missed something obvious in creating the model.

Does anyone know what i might have done wrong?

thanks for your help.

 

[ctmfab]

The latest version of Risa 3D uses "physical" members that will automatically attach themselves to the intermediate nodes. So, you no longer have to break a continuous beam at the various nodes along it's length. However, the unsupported length used in the AISC calcs will be set equal to the full length of the member. If this is not the condition and intermediate supports exist, you must set the unsupported length by entering a value for the member. But, the AISC unsupported length won't change the moment diagram.

Some things that might help eliminate the "locked" nodes.
1. Make sure you have used the model merge.
2. Ensure that you have appropriate boundary conditions specified. Such as where the frame meets the ground.
3. Check each member's end releases to ensure that the member is not free to displace on both ends. For instance, X-shear may be released on one end, but not both. Also, you can't release a force from the member at one end then also at a boundary condition on the other end.

If you don't have the latest version, download a trial version at

http://www.Risatech.com.

(No I am NOT an agent of Risa). It is a helpful and free tool to use. No time limit, only maximum node limits if you want to save the model.

 

[fish1]

Thanks for your help ctmfab.

I revised my model by converting the longer member into multiple from node to node. The results were reasonable with the new model without error messages.