Robot Structural Analysis

## Robot Structural Analysis

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Posts: 10
Registered: ‎06-28-2011
Message 1 of 7 (2,523 Views)

# Meshed slab supported by beams

2523 Views, 6 Replies
09-22-2011 05:22 AM

Hi

I'd like to support a concrete slab by a concrete or steel beam.

I'm interested in the moment distribution for the beam, and in the mean time would like to know the moment distribution for the slab (e.g. Bottom reinforcement...). How can a model be set up which combines those two results? Because once the slab has been meshed, also the supporting beams are divided into elements and the expected (global) moment distribution for the beam isn't shown.

See attachment 1: meshed slab.

See attachment 2: slab without finite elements and 'normal' moment distribution in the beams.

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Message 2 of 7 (2,466 Views)

# Re: Meshed slab supported by beams

09-23-2011 01:11 AM in reply to: Casparov

Hi

I am not sure whether I am answering for your question or not but in case of RC beams you can turn on option of considering slabs and then see results for such beam in Forces table.

﻿

Rafal Gaweda
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Posts: 10
Registered: ‎06-28-2011
Message 3 of 7 (2,443 Views)

# Re: Meshed slab supported by beams

09-23-2011 03:25 AM in reply to: Rafal.Gaweda

Hi Rafal

I can't see the image above.

What I would like to build is a model that combines both slabs and beams (be it steel or concrete beams) in such a way beams and slabs don't work together (i.e. the rigidity of the slabs should not influence the results created for the beams). So, the beams only act as a line support for the slab, and the slab only distributes its load onto the beam (e.g. Moment in the beam = PL²/8), as we'd do in an easy and quick hand calculation.

As you can see in the model in attachment, slab and steel beams are both influencing each other (working together)?

The load onto the slab equals 100 kN/m², and the slab is 10m by 10m. So the load onto the beams equals 500 kN/m as the slab is only distributing load in towards the beams, resulting in:

1. Moments M = PL²/8 = 6250 kNm (i.o. 5265.91 kNm)
2. Shear force V = PL/2 = 2500 kN (i.o. 2233 kN)

So actually, I'd like to know if there's a possibility of both seeing a moment and shear force distribution in the slab, and the moment and shear force distribution for the supporting beams as we'd expect.

To make my question a bit more understandable, we're designing a structure which uses prefabricated (also prestressed) hollow floor slabs and beams. To determine which slabs we should use, the contractor provided us with an easy to use guide containing all resistance moments and shear forces for any of the slabs and beams we'd like to use. For this, we assume the connections between slab and beams are not rigid (moment connections...), but the beams are just supporting the slabs.

Regards,

Casper

Edit: the slab in the above example is 300 mm high, C12/15 concrete quality; Deck slab (one-way): Shell FE, One-way load distribution and no diaphragm. The supporting beams (simple bars) are HEA1000, S235 steel quality.

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Message 4 of 7 (2,417 Views)

# Re: Meshed slab supported by beams

09-23-2011 04:42 AM in reply to: Casparov

If you want to see such results you have to use cladding with unidirectional distribution of loads instead of slab panel

Rafal Gaweda
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Posts: 609
Registered: ‎09-07-2011
Message 5 of 7 (2,344 Views)

# Re: Meshed slab supported by beams

09-26-2011 10:41 PM in reply to: Rafal.Gaweda

Casparov,

Instead you can use an orthotropic slab with no transverse stiffness.

Note that Robot won't let you put in zero (0) for "n2" in the definition box.  Enter it as 0.00001, then run your calculation.  When you re-open the definition dialogue box it will be blank.

This will then get you pretty close to the results you are after

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Registered: ‎09-07-2011
Message 6 of 7 (2,340 Views)

# Re: Meshed slab supported by beams

09-26-2011 10:43 PM in reply to: tony.ridley

note my slab is 250 thick solid concrete, shell element, no diaphragm.  I have not used linear releases on my slab at the beam interface like you did.

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Message 7 of 7 (2,264 Views)

# Re: Meshed slab supported by beams

10-05-2011 02:13 AM in reply to: tony.ridley

Tony

Thank you very much for your help. Your solution resembles the closest to the results I expected.

Thanks again.

Casper

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