topic Re: Suspended slab - shear results in Robot Structural Analysis Forum

Suspended slab - shear results

Anonymous — Tue, 21 May 2013 11:59:51 GMT

Hello.

Could you please help me with understanding the results I'm getting. I need to anylise elastic shear in suspended slab. The attached pdf shows a map for shear forces in x-x direction and the cut taken in exactly the same place. I'm trying to understand which values should I be looking at. The very high value of 968.99kN does not show on the cut as well as the value next to it 649.15kN. Instead I've got value of 538.53kN (the last print screen overlays the shear map with cut through). I haven't used the 'reduced forces above supports' option.

My questions are:

- which value is the elastic shear I should be considering

- should I switch on the option with 'reduced forces above the support'

- is there any way of reading values along the cut/diagram in any chosen place

Thank you very much in advance. Your guidence has been a life-saver for me. Kind Regards.

Re: Suspended slab - shear results

Rafacascudo — Tue, 21 May 2013 12:27:30 GMT

Without knowing the panel local X direction it is Impossible for us to know what the map is showing ,if you choose automatic direction for the panel map.

Best way is to choose local X according to Global X if they are in the same direction.

Same for panell cuts. Best way in panel cuts is , instead of automatic ,choose local of the cut. Then ,in detailed , if you choose Qxx , it wil show the shear across the cut. If you choose Qyy ,it wil give you the shear along the cut.

Re: Suspended slab - shear results

Anonymous — Tue, 21 May 2013 12:57:17 GMT

Thank you for quick reply.

The local directions of the panel are same as general X Y Z. I've changed the settings in Detailed to Direction X for both - map and cut, and results are the same. Please find attached pdf. Also included an enlarged view of my slab for clarification. I don't know which value is the one I need.

Re: Suspended slab - shear results

Pawel.Pulak — Wed, 22 May 2013 14:51:03 GMT

Wioletta,

answering various topics raised by you

1/ The extreme values displayed on the map can correspond or to nodes of FE mesh or to centroids of finite elements.

Your screen captures do not show finite elements on maps (it can be done activating "With FE mesh") but positions of descriptions and shapes of maps suggest that extreme values ARE NOT observed on the line along global X passing through the supporting column. The cut IS defined along such line so the differences between map and cut are justified. Moreover the gradients of shear force on the map are very big close to the column so small distance corresponds to big difference of force.

2/ In the first post you have asked "is there any way of reading values along the cut/diagram in any chosen place".

It is possible using "Diagram analysis" see the screen capture below and this video.

3/ It is possible to obtain total shear transferred between slab and column defining cuts around the column and integrating shear forces along them but as you see these are areas of very big gradients of shear forces and precision of shape functions of surface finite elements in such areas can be very poor. If it cannot be avoided then it is recommended do define cuts over centroids of finite elements where this precision is relatively the best.

But in the situation like yours the best solution is to use forces and moments from the top of supporting column. These values precisely describe the transfer of forces from the slab to the column.

Regards,

Re: Suspended slab - shear results

Anonymous — Wed, 22 May 2013 14:57:07 GMT

Pawel,

I understand now. I appreciate your time. Thanks.