STAAD model steel utilization ratios go SKY HIGH with just changing some WWF column members using Canadian Code

Hi,

My company is working on a steel structure analysis model that is giving us very unusual results when we change some WWF550x420 members to standard rolled shapes.  

For example, if we change the WWF550's to W610x262's the model's utilization ratios blow up all over the structure (ratios that are more than 10 and much higher!) and for some members the "member design fails".

The other member far away from this area should not be failing because of a column size change.  It looks very unusual and we cant figure out why it is doing this.  Please help!  

We are running STAAD Connect V22 Update 3.

Thanks!

  • We think we solved the issue.  The columns we originally selected supporting the cantilevered box truss above were so heavy and stiff they were able to compensate for lateral flexibility of the box truss.  When reducing the columns to something lighter (less stiff), the deflections of the overall structure became too much for the stiffness matrix and the structure essentially collapsed.  By adding some moment transferring portal frames in the box truss, the structure was stabilized and the lower support columns could be further optimized.