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stroxy
Posts: 183
Registered: ‎12-06-2011
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Slab loads to beams

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03-01-2013 05:36 AM

I have a finite element model consisting of 2 way spanning slabs supported by beams.  After viewing the panel cuts for the self weight shear force diagram, I notice that cut A1 and A3 are not behaving as I would expect, which is that the shear force diagram would change signs over beams 2549 and 2553. As a result, the beams are very lightly loaded. Is there a logical explanantion or am I missing something.

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Artur.Kosakowski
Posts: 4,544
Registered: ‎12-17-2010

Re: Slab loads to beams

03-01-2013 06:47 AM in reply to: stroxy

The beams being not significantly stiffer than the slab? Try to offset them below the slab or increase its moment of inertia as described:

http://forums.autodesk.com/t5/Autodesk-Robot-Structural/T-slab/m-p/3185418

 

http://forums.autodesk.com/t5/Autodesk-Robot-Structural/Beam-offsets/m-p/3332921

 

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Artur Kosakowski
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stroxy
Posts: 183
Registered: ‎12-06-2011

Re: Slab loads to beams

03-01-2013 07:10 AM in reply to: Artur.Kosakowski

I kind of suspected that.  OK Thanks!!

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stroxy
Posts: 183
Registered: ‎12-06-2011

Re: Slab loads to beams

03-01-2013 07:16 AM in reply to: stroxy

One issue comes to mind.  In seismic analysis we are supposed to actually reduce the moments of inertia of frame members to increase the building period.  Actually my beam elements have reduced moments of inertia in the analysis module and that may also be further contributing to the problem.

 

Am i correct to reduce for vertical elements and maintain that of beams.  

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Artur.Kosakowski
Posts: 4,544
Registered: ‎12-17-2010

Re: Slab loads to beams

03-01-2013 07:40 AM in reply to: stroxy

Then I think this approach should be applied to both beams and slabs (as well as columns).



Artur Kosakowski
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stroxy
Posts: 183
Registered: ‎12-06-2011

Re: Slab loads to beams

03-01-2013 07:56 AM in reply to: Artur.Kosakowski

Sounds like a plan!! Thanks

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stroxy
Posts: 183
Registered: ‎12-06-2011

Re: Slab loads to beams

03-11-2013 12:40 AM in reply to: Artur.Kosakowski

in reference to your post, I have a uni-directional box floor with stiffnes matrices as attached and I want to reduce the stiffness matrix by 50%.  do I reduce all clouded values in the attachment by 50% to be code compliant?

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Artur.Kosakowski
Posts: 4,544
Registered: ‎12-17-2010

Re: Slab loads to beams

03-11-2013 01:57 AM in reply to: stroxy

Correct.

 

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.



Artur Kosakowski
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