How do you rotate a member (ie W-Shape Column) so it is acting in weak axis bending?

Aaron Jobst

I am trying to check the capacity of  member in a braced bay that should be oriented for weak axis bending.  To model the bay I have created a simple 2D model as I only have loads in Global X and Global Y directions. The column supports in my model are generated with the local x axis perpendicular to the Global-X (ie performing in the direction of the strong axis). However, i would like to rotate my shape so the local-x is in the same direction as the Global X so my column act in the member's weak axis.

The 2D model type Member orientation Tool options only show Toes Up or Toes Down, which does nothing for doubly symmetric W shapes. I have tried selecting the Columns by right click to reoriented the column. This appears to work with the model render tool, however the model reverts the columns back to strong axis direction when I run the analysis and check in the model in S-Steel. S-Steel code check compares the loads against the columns  strong axis properties.

Andres Chavez

Hello Aaron,

 

Thanks for reaching out. Andrés here, it is my pleasure to greet you again. I'll be glad to answer your questions.

We appreciate the elaboration. In this case, considering that you are working with a 2D model, S-FRAME will automatically take the section's strong axis for its calculations. As you have pointed out, the 'Toes Up/Toes Down' option is only for rendering matters, and it will have no effect on the results. The Member Axis Orientation Tool topic in S-FRAME's Internal Help System discusses this more in detail, we'd recommend reviewing it.

With that said, we could try one of the following options. The first one is to work with the 2D model and create a custom section with the weak axis' section properties and analyze it. For the second one, which is more recommendable, we could try converting the model to a 3D model, by changing the Model Type to a 3D Frame (menu bar, Settings -> Model Type).

This will allow us to use the Member Axis Orientation Tool to rotate our columns to have the loading acting on their weak axis, which will be effectively taken into account for the analysis:

If our member's local X axis does not match the desired column's orientation, we can always revert our member's local X axis by selecting the members we want to modify, clicking on the Edit -> Move, toggling on the 'Rotate Local Axis' option, and clicking on 'Ok':

We hope this information is helpful. Feel free to ask any additional questions, we're here to help.

 

 

Kind regards,

 

Andrés Chávez Burgos

AEC Solutions Engineer