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Valued Mentor
AJA14
Posts: 490
Registered: ‎11-01-2011

Steel Beam Releases

776 Views, 9 Replies
12-15-2011 05:01 AM

Hi,

 

    I am currently designing a steel structure with deck slabs. pinned - pinned releases have been applied to the joists but they seem to be carrying negative moment. In addition, the moment diagram looks irregular and I was thinking maybe it is because the stiffness of the girder is much greater than that of the joist. Why is this happening. Please refer to the attached image.

Ali Al-Hammoud
Structural Design Engineer
MZ & Partners Engineering Consultancy
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Product Support
Rafal.Gaweda
Posts: 4,971
Registered: ‎04-26-2010

Re: Steel Beam Releases

12-15-2011 05:08 AM in reply to: AJA14

If you do not mind please attach view of whole structure indicating the element of your interest or send us model.

PLates, Diaphragms there?



Rafal Gaweda
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Valued Mentor
AJA14
Posts: 490
Registered: ‎11-01-2011

Re: Steel Beam Releases

12-15-2011 05:13 AM in reply to: Rafal.Gaweda

The attached image shows the joists supported on the girder which is supported on two columns at its ends. The panel on top of them is a shell element of 10 cm thickness. I usually study the joists using a shell element and use cladding to study the main girders. Anywyas, I still don't understand the reason for the negative moments in the joists.

Ali Al-Hammoud
Structural Design Engineer
MZ & Partners Engineering Consultancy
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Product Support
Rafal.Gaweda
Posts: 4,971
Registered: ‎04-26-2010

Re: Steel Beam Releases

12-15-2011 05:40 AM in reply to: AJA14

So ...

Sharp diagram - it depends on mesh - then more refined mesh the smoother diagrams

Negative moments - I guess joists without releases or... check Private Message

 

diagram.jpg



Rafal Gaweda
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Artur.Kosakowski
Posts: 4,586
Registered: ‎12-17-2010

Re: Steel Beam Releases

12-15-2011 06:09 AM in reply to: AJA14

AJA14 wrote:

. Anywyas, I still don't understand the reason for the negative moments in the joists.


I assume the beams are released but the slab is bi-directional and not released along the edges. See the difference.

 


 



Artur Kosakowski
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New Member
nsmokrovic
Posts: 2
Registered: ‎07-15-2013

Re: Steel Beam Releases

07-15-2013 07:35 AM in reply to: AJA14

Hi!

 

 

I have a similar problem (Picture1) and haven't found the solution in this discussion. Maybe you have some new knowledge. So, if I mark beam as pinned-pinned, why do the results show that there is a bending moment at the one end of the beam? 


Thanks, 

 

Nikolina

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Rafal.Gaweda
Posts: 4,971
Registered: ‎04-26-2010

Re: Steel Beam Releases

07-15-2013 07:38 AM in reply to: nsmokrovic

Nikolina,

 

File, please.



Rafal Gaweda
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New Member
nsmokrovic
Posts: 2
Registered: ‎07-15-2013

Re: Steel Beam Releases

07-15-2013 08:13 AM in reply to: Rafal.Gaweda

Here is the link to download: http://www.filemail.com/d/hnrawqbwpvjgidl

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Rafal.Gaweda
Posts: 4,971
Registered: ‎04-26-2010

Re: Steel Beam Releases

07-15-2013 08:27 AM in reply to: nsmokrovic

Quick hints:

 

- you need to correct model first to get correct results (to get rid of instabilities) - start from deleting releases from bottom of columns - on side of pinned supports

- you need to make this model  \ loadcases or at least cominations converged, otherwise results are wrong

 



Rafal Gaweda
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Product Support
Rafal.Gaweda
Posts: 4,971
Registered: ‎04-26-2010

Re: Steel Beam Releases

07-16-2013 01:36 AM in reply to: Rafal.Gaweda

Nikolina,

 

my understanding of this model ; remarks + corrections:

 

- claddings should not be overlapped \ dupicated on certain areas (in attached model walls and flat parts of roof corrected ; correct arcs roof claddings)

 

cladingsnik.jpg

 

- claddings not defined accurately (overlapping by centimeters) also

- releases from columns removed

- Support_1 defined and used

- ry support defined and used to block possibility of bottom chord beams rotations (or modify trusses by your own to block beams rotations)

- Pinned1_Fixed release defined and used to block arc beams rotations

- remodeled bracings  8to22By2 1882 1922to2104By13 2129to2324By13 3031to3037By2 3038to3044By2  - (previously defined bracings are instable)

 

File :http://we.tl/KIxDdpLqoi

 



Rafal Gaweda
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