topic Re: Core Wall Results in Robot Structural Analysis Forum

Core Wall Results

keith483GL — Sat, 19 Mar 2022 16:36:16 GMT

Hi All,

I am having a problem trying to interpret core wall results.

My Mx and My diagrams are sawtoothed (positive moment at bottom of panel and negative at top) in nature as opposed to gradually increasing like the Fz diagram. So the moment should be 0kNm at the top of the wall and a maximum at the base.

I am also getting large torsional moments Mz for cores. This question has been asked before, however, I don't understand the solution. If I calculated the forces in the walls via hand, I would account for the torsion by transforming into shears in the walls, and hence increase Mx or My moments. Is ROBOT doing this transformation?

Any help gratefully received. Thanks.

Re: Core Wall Results

TienDat.NGUYEN.Engineer — Tue, 22 Mar 2022 03:40:59 GMT

As I understand, the axis of wall you use in the model will be like this

In this case, for the 1st question you want to see the moment of the wall under horizontal load, but it depends on the boundary connection on bottom and top. Not all the case it will be the largest at bottom and zero at top as the vertical cantilever.

2nd question, the moment Mz will transfer the tension/compression force in wall (not the shear) and it doesn't increase the bending moment of Mx My because Mz is the in-plane moment.

Re: Core Wall Results

keith483GL — Tue, 22 Mar 2022 10:40:21 GMT

Thanks for the response @TienDat.NGUYEN.Engineer, however, I don't agree with your reasoning for point 1.

For a single wall I get the following horizontal shear distribution over the height of the wall:

The bending moment at the base of the wall in accordance with the above shear force profile should be 5235.4kNm. I am getting the following bending moment profile, which is intuitively not correct:

I am really confused. The bending moment should vary roughly linearly from 5235kNm at the base to 0kNm at the top.

I have modelled the slabs as rigid diaphagms - could this be a reason?

Any help or explanation welcome.

Thanks.

Re: Core Wall Results

TienDat.NGUYEN.Engineer — Wed, 23 Mar 2022 07:42:41 GMT

As I understand, the orientation of bending moment with 5235 kNm at the base to 0 kNm at top act like the cantilever. In this case I'm not sure if it's corresponding to this behavior or not.

Could you please attach the RSAP model also ?

Re: Core Wall Results

keith483GL — Wed, 23 Mar 2022 09:57:11 GMT

Hi @TienDat.NGUYEN.Engineer thanks again for responding.

The model is attached if you would be so kind to review.

Thanks,

Keith

Re: Core Wall Results

Krzysztof_Wasik — Wed, 23 Mar 2022 10:43:18 GMT

Hi @keith483GL

In my opinion slab defined as rigid diaphragm (full stiffening ) causes this effect

In your model results diagrams for core walls looks as follows.

When flexible diaphragm calculation model (stiffening in XY) is used for slabs diagrams looks as expected.

Similar effect can be observed for simple 2D frame for middle column simulating core wall, when beams are defined as rigid members (right diagram) and flexible members (left diagram)

Re: Core Wall Results

keith483GL — Wed, 23 Mar 2022 12:12:46 GMT

Thanks @Krzysztof_Wasik this looks a lot more sensible. I will use slab-flexible diaphragm going forward.

The top of the core bending moment diagrams in your example and my model still look a bit funny. Why is this happening? It would be good to understand this.

Many thanks again.

Re: Core Wall Results

Krzysztof_Wasik — Wed, 23 Mar 2022 12:20:13 GMT

Hi @keith483GL

You will obtain smooth diagram when beams will be connected to colum with pined connections.

Re: Core Wall Results

keith483GL — Thu, 24 Mar 2022 09:22:28 GMT

Thanks @Krzysztof_Wasik how do you model flexible diaphragm connections to core walls as pins?

I understand beam to column connections, however, my structure is flat slabs. So a full concrete plate as opposed to discreet beams.

Again, any help gratefully received.

Thanks.

Re: Core Wall Results

Krzysztof_Wasik — Thu, 24 Mar 2022 09:27:43 GMT

Hi @keith483GL

You can define linear releases between slabs and core walls. (Geometry >Additional attributes>Linear releases) but since core wall is connected with slabs in more than one node (along lines), in mode cases you will not avoid "funny" diagrams for core walls moments when slab stiffness is regarded while calculations.