Robot Structural Analysis

## Robot Structural Analysis

Distinguished Contributor
Posts: 145
Registered: ‎01-24-2009
Message 1 of 5 (424 Views)

# Offsets and equilibrium of moment at the node

424 Views, 4 Replies
12-14-2011 01:47 PM

Hi All,

I did some tests to using offset  in order to simulate actual conditions in which two different beams frame into a node. The slab supported by the principal beams is simulated as an orthotropic flexible on the xy plane diaphragm as shown in picture.

The offset influence on the structure behavior is not clear. I don’t understand.

If you consider the beam 33 and the column 14 and try to test the equilibrium of the moments for the node 23 in YZ plane you will find the following values (beam 33 and column 14 have the same Y local axis direction):

Beam 33  My =26.55

Colum 14 My = -67.03

Beam 34 Mx = -0.52

Beam 40 Mx = 0.52

The equilibrium of moment = -67.03 +26.55+0.52+0.52 = not equal to 0

In the same situation if you don’t apply the offsets the situation changes.

Beam 33  My =47.95

Colum 14 My = -50.04

Beam 34 Mx = -1.04

Beam 40 Mx = 1.04

The equilibrium of moment = -50.04 +47.95+1.04+1.04 = near to 0

how can I check the accuracy of results ?

Any suggestion ?

Product Support
Posts: 424
Registered: ‎06-23-2008
Message 2 of 5 (412 Views)

# Re: Offsets and equilibrium of moment at the node

12-14-2011 11:46 PM in reply to: GabrieleNovembri1027

Hi Gabriele,

if you have defined the offset in local Z for beam 33 you should consider additionally the moment resulting from FX*offset for this bar.

Moreover some component to moment equilibrium can be given by the plate (its magnitude depends on orthotropic plate properties you defined).

---------------------------------------------

Best regards,

Pawel Pulak
Distinguished Contributor
Posts: 145
Registered: ‎01-24-2009
Message 3 of 5 (403 Views)

# Re: Offsets and equilibrium of moment at the node

12-15-2011 01:51 AM in reply to: pp2008

Hi Pawel,

I understand the Fx contribute to the equilibrium of the node. But what about the torsion moment of the two beams framing into the node (in normal situation o when they have an offset along z axis) ?. Moreover how I can understand the contribution of the ortotropic panels if I don't have any result for that element ?.

As you understand the problem is to explain to someone that in my structure the beam  and the column framing in the same node have a different value of the moment.

Do you have some technical description of the procedure used by Robot ?

Thanks

Product Support
Posts: 424
Registered: ‎06-23-2008
Message 4 of 5 (396 Views)

# Re: Offsets and equilibrium of moment at the node

12-15-2011 03:16 AM in reply to: GabrieleNovembri1027

Hi Gabriele,

If beams 34 and 40 have also non-zero offset in local Z you should consider in equilibrium of node 23 not only torsion moments MX from them but also moments resulting from horizontal shear: FY*offset

As concerns participation of the panel in the transfer of moment you can display maps of moments - but it will not give you precisely the participation of slab in node 23. This participation can be obtained as non-zero value when considering all bars adjoining in specific node. If panel would be deleted then equilibrium considering all bars adjoining in specific node should give precise zero.

---------------------------------------------

Best regards,

Pawel Pulak
Distinguished Contributor
Posts: 145
Registered: ‎01-24-2009
Message 5 of 5 (376 Views)

# Re: Offsets and equilibrium of moment at the node

12-15-2011 06:52 AM in reply to: GabrieleNovembri1027
thanks

Recently Solved