Why do the Vierendeel bending results differ between Tekla Structural Designer and the Kloeckner Westok Cellbeam software?

Question

Why do the Vierendeel bending results differ between Tekla Structural Designer and the Kloeckner Westok Cellbeam software?

Answer

There is a difference between Tekla Structural Designer and Kloeckner Westok Cellbeam in the distribution of the loading for the Vierendeel bending checks.

Both checks will use the Sahmel method at 2.5 degree intervals around the opening and both pieces of software will calculate the critical angle.

In determining the shear distribution for composite beams, both programs take into account the resistance of the slab. The Kloeckner Westok software adjusts the vertical shear to attempt to achieve a zero moment across the web post. Shear is distributed away from any failing tee and this then forms the initial distribution for the Vierendeel check. If at the critical angle the tee fails, this shear is then redistributed to attempt to achieve a pass.

Tekla Structural Designer preferentially distributes the shear to the top tee and if at the critical angle the top tee fails then the shear is ‘pushed’ down into the bottom tee. The redistributed shear for the Vierendeel check is taken as the start point for the horizontal moment check with some additional redistribution if the horizontal moment fails. The final distribution is rechecked for Vierendeel bending.

The above processes provides a consistent shear distribution for these checks.