How to work properly with section cuts ?

[ThisMustBeAJoke]

Hi, i have modelled a building that suffered severe torsional damage under effects of recent earthquakes. The model only consists shell elements so i am using section cuts (with grouping) for checking the torsional moments. But something is unclear for me. For getting a good measure from (let's say it consist 2 blocks sideways) a column should i group all of the joints or only one joint ? i selected all the joints but after reinforcing the building model, torsional MODAL shape calculated at third modal shape but torsional moments decreased only a little for example 13 kNm to 10 kNm. So i thought i am looking to wrong results because building is no longer twists but torsional moments are almost same. What should i do ? By the way i am looking torsional moments caused by SERVICE LOADS + EARTHQUAKE(response spectrum) combination.

 

[Agent666]

It would seem defining a pier on each wall to read off the results would do the same thing you're trying to achieve.

You're trying to extract each walls design actions at the base right?

https://engineervsheep.com

 

[Agent666]

Actually scratch that, you're in SAP not etabs.... My mistake.

Etabs is probably better for a walled structure as it has tools for automatically integrating shell element actions.

But for a defined section cut based on groups, I'd suggest making a little test model of a cantilevered wall and apply a known load and play around with the grouping to test to ensure you're both defining the section cut and reading off the results correctly.

If modelling an existing structure, modelling rigid supports may not be so realistic. Allowance for soil-structure interaction may be required.

https://engineervsheep.com

 

[ThisMustBeAJoke]

I know etabs better for this but not all my colleagues using it now so we are using sap unfortunately.

I know how the section cuts work but don't know why some walls perpendicular to the X axis giving defected values or they really torsioning a lot.

But can't be that's why i am asking. Probably some mistake about local axes but couldn't find it.

Also i know about the stuff that you mentioned but currently we are researching something else. But thanks for the answer anyways.

btw i can contribute your website with python scripts if you want.

 

[Agent666]

In etabs I believe you select all the shell elements and the joints at the location you want the section cut result, and define that as a group. Then define a section cut using that group. I'd imagine SAP2000 is similar.

I find it isn't the most intuitive process, and I always have to setup a little test model (like a cantilevered wall) to both make sure I've set it up correctly, and that I'm interpreting the results correctly.

https://engineervsheep.com

 

[Brad805]

If you are using a lot of section cuts in SAP2000 there is an Italian that has a nice add on. Link It greatly improves section cuts and provides nice diagrams of the forces. If you are doing non-linear or layered elements, it is not currently setup for that.

I usually have section cuts for all members at one level where I know the total shear. When you export to excel you can easily check your total value is correct.