ETABS Shear Wall Design EC

[Redtelis]

Hi guys,

I am about to design a core wall and I am trying to validate by hand the ETABS Shear Wall design results based on Eurocodes.

Within the Design Load Combinations for the Shear Wall Design, I choose all my ULS load combinations (i.e. wind leads,live leads etc).

The thing is that I am struggling to understand how ETABS chooses the worst case scenario between the load combinations.

Does it choose the worst case load combination by checking which combination gives the highest moment?

I am a bit confused because during the Shear Wall Design, the axial load that ETABS takes into account its not within the table results for this specific pier and location. I have also removed the live load reduction factor but still the axial load of the design process doesn't match with the axial load of the corresponding load combination!

Regards

 

[Trenno]

Firstly, go to Help > Documentation > Shear Wall Design > EC2. Make yourself familiar with how ETABS goes about it's shear wall design.

In regards to load combos - remember shear wall design is governed by a P/A +/- M/Z approach, therefore you can max compression or tension on either end under different combinations. This will form the envelope to the flexural design of the wall.

Similarly, axial load can influence shear capacity of walls (ie tension with shear).

Therefore it may be the case that there won't be one single governing case.

If you look through the tabular output for the pier forces, the axial force P should appear somewhere in here.

 

[Dowels93]

I might have read this wrong years ago, but I believe ETABS:
1) plots an interaction diagram (P vs M) for the wall
2) plots the various loading points
3) draws lines from the origin through each point to find where the line intersects with the interaction diagram envelope (interpolated between diagrams if biaxial bending present)

Where the point falls along the line between the origin and the diagram envelope is the utilization ratio, which is what I believe ETABS reports for the design check ( >1 means that it is beyond the envelope of course). If you go to Design -> Display Design Info -> Right click on the wall, then the results will tell you which load combination it has determined to be the worst case for flexural and shear design (similar to below).