Building Sway Lateral Wind Results

[Anonymous]

Hi Guys

Would like your advice here. I've got a 40+ storey building right now that I've modelled in Robot.

In particular I'd like to look at a relatively accurate building sway figure for wind lateral wind load. I've run my model in RSA and its giving values in the order of 180mm; however I've run an equivalent test in Etabs which is giving values in the order of 500mm. In both models I've reduced the Ig to 0.35Ig.

In Robot, editing the Ig value didn't seem to make a difference for sway which is very strange; as I still got values of 180mm where as I would of expected it to change significantly.

Grateful if someone can assist. I've attached the model here for reference. I'm trying to model the columns as pin-pin and using the core walls for lateral stability. The floors are modelled as rigid diaphragms except L2 which is a transfer plate and modelled as a shell.

My main question is as follows:

1. Have I reduced the Ig values correctly in the model?

2. Am I modelling it correct/feedback would be great.

3. Tips and tricks to get Robot to give accurate sway values?

Cheers

Jim

[Artur.Kosakowski]

I'd suggest running a smaller scale model first so that it is easier to compare results after making a change to some parameters as working with 40 story building to determine the correct way of modelling it may not be that easy. First of all by reduction  of Ig in ETABS do you mean out if the wall plane stiffness  or in-plane stiffness? Perhaps you should define a cantilever build from panels defined one above another and compare displacements for such simplified model first?

[Anonymous]

Thanks for the reply Arthur

Im referring to both in plane and out of plane stiffness reduction.

I've realised my problem is to do with having to modify the property of my core walls under the  'Orthotropic' tab.

In Etabs; I've got f11,f12, f22 =0.35. m11, m12, m22 =0.35 also (will reduce out of plane bending later if Im getting too high results).

In Robot, I've tried to do the same: f11,f12, f22 =0.35. m11, m12, m22 =0.35. I assume they relate to the same factors for Etabs. (I want to reduce the in-plane and out of plane stiffness)

I've tried to run a test model and now I'm getting instability within the mesh nodes.

Can you assist? Grateful for your thoughts.

Jimy

[Artur.Kosakowski · Accepted solution]

Please watch Robot webinar 16 (the recording is available from http://forums.autodesk.com/t5/robot-structural-analysis-forum/robot-structural-analysis-webinars/td-...) and focus on the slide 21 

I'd suggest setting the direction of the orthotropy for walls as Direction Z 

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[Anonymous · Accepted solution]

Thanks Arthur.

James