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RE: modeling composite beams in SAP2000

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The strength of the composite section will have no correlation with the
calculated elastic stresses. If you must use a computer model, you need to
use an equivalent section and move on with the design.

Rex Donahey
Composite Technologies
-----Original Message-----
From: Leopoldo Sanz [mailto:leopoldosea(--nospam--at)]
Sent: Wednesday, June 14, 2000 8:00 AM
To: seaint(--nospam--at)
Subject: Re: modeling composite beams in SAP2000

Dear Majid:
Thank you very much for your attention. I have a new question:
The model we're talking about (two elements connected only by joint
constraints between every pair of nodes) is very good for the composite
section, but:

How do you compute the final strength on the steel beam as a contribution of
the initial stresses (basicly a product of the steel beam, steel deck and
concrete slab self weights loads) resisted by the bare beam section and the
post-composite stresses (live loads, floor, etc.) resisted by the composite

We must first compute initial stresses on the bare beam section. Then we
have to analize the composite section, acting only post-composite loads,
wich do not include steel beam, stell deck and concrete slab self weights
but live loads and any other post-composite applied loads.

How do you account for the contribution in stresses of the different
construction stages?

I can only figure to make two models (one for the bare beam section and the
other one for the composite section) and then make hand calculations in a
spreadsheet. Although, if I have to do this, I think it will allways be less
time consuming to use an equivalent section and go ahead.

What do you do?

>From: Majid Sarraf <msarraf(--nospam--at)>
>Reply-To: seaint(--nospam--at)
>To: seaint(--nospam--at)
>Subject: Re: modeling composite beams in SAP2000
>Date: Tue, 13 Jun 2000 18:17:47 -0700
>I have had a good success in using SAP2000 to model composite girders. In
>fact I verified the results by checking them against field measurements,
>and they are in very good agreement.
>The key issue in modeling composite action is to constraint only pair of
>nodes with different labels, and not all concrete nodes to those of steel
>top flange with one lable. So it would be a bit tedious to define different
>constraint for every pair if you have too many nodes along the girder. The
>best way then is to go to *.s2k file and use a pre-processor program to
>compile constraint section of the input file.
>Majid Sarraf
>National Bridge Research Organization (NaBRO)
>At 10:14 AM 6/13/00 -0700, you wrote:
>>Dear Leopoldo,
>>As far as m experiences, an easy way is just define an
>>equivalent section and go ahead by that. Although to
>>model steel and concrete parts together, you can
>>define two element, but the output generated by SAP
>>design module won't be accurate enough. Because the
>>model doesn't have an accurate definition of a
>>composite beam.
>>Good luck,
>>--- Leopoldo Sanz <leopoldosea(--nospam--at)> wrote:
>> > Dear friends:
>> > Is it possible to model composite beams in SAP2000
>> > without doing hand
>> > calculations? May I simply specify effective width,
>> > slab concrete f'c, E,
>> > etc.? Where?
>> > Thank you very much
>> > Yours,
>> > Leopoldo Sanz
>> >
>>Fariborz Tehrani,                      Phone: (310)509-8826
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