Composite beam in STAAD
Composite beam in STAAD
(OP)
Hi,
I am trying to model a composite beam (steel beam + concrete slab).
For this purpose I modeled my composite beam as a steel beam and plate elements.
I applied then an offset distance 0.95 m to the steel beams.
Now I see that the steel beam gets a very large axial force and the Mz moment at the mid span is very small!!!
I am really confused the way STAAD calculates section forces.
Do you have any clarification on this?
Do you have any sample for a composite beam used in STAAD (built-in Composite Deck)? Could this feature used on user defined beams such TAPERED?
I have uploaded my input file.
Thank you
Bill
I am trying to model a composite beam (steel beam + concrete slab).
For this purpose I modeled my composite beam as a steel beam and plate elements.
I applied then an offset distance 0.95 m to the steel beams.
Now I see that the steel beam gets a very large axial force and the Mz moment at the mid span is very small!!!
I am really confused the way STAAD calculates section forces.
Do you have any clarification on this?
Do you have any sample for a composite beam used in STAAD (built-in Composite Deck)? Could this feature used on user defined beams such TAPERED?
I have uploaded my input file.
Thank you
Bill





RE: Composite beam in STAAD
RE: Composite beam in STAAD
I mean small bending moment and large axial force.
Unfortunately, I don't have any other software to verify the results.
Suppose this is a bridge deck, what shall we do if the section forces are not correct.
Steel beams fail when I apply a check code due to large axial forces.
It doesn't make sense at all.
Does STAAD calculate the section forces correctly?
Do you know how I can get arround this situation?
Thanks
Bill
RE: Composite beam in STAAD
RE: Composite beam in STAAD
I did as you suggested.
I still get axial force.
What do you think?
I have attached my modified model.
Bill
RE: Composite beam in STAAD
The slave master commands only apply to a floor diaphragm.
RE: Composite beam in STAAD
I don't know how I can make a rigid floor diaphragm.
Just wonder if you mind helping me on this?
Again thanks a lot.
Bill
RE: Composite beam in STAAD
If this is a single beam, I suggest hand calculations.
RE: Composite beam in STAAD
Do you know how I can get rid of the axial force in the beam?
I have used the EXPLICIT definition method in STAAD to create a composite beam (CM.std)
The steel beam and concrete slab act monolithically and as expected for load case 1, max Mz=5000 kNm, but it doesn't work for the temperature load (Shrinkage).
How can I get around this problem so that I get Mz=5000 kNm in my previous model?
Bill
RE: Composite beam in STAAD
RE: Composite beam in STAAD
RE: Composite beam in STAAD
Thanks for your reply.
I am glad to hear that you have successfully modeled a composite beam in STAAD. I was about to give it up and try other software for this problem.
Have you applied MEMEBER OFFSET command to steel girders?
I have done the same, but the max mid span moment is not correct due to huge axial force in the girders!
Could you please if possible upload your model so that I can see what you have done to overcome this problem?
Thanks
Bill
RE: Composite beam in STAAD
The model you have is correct. If you look at the bottom flange stresses in the girder they will be close to the bottom flange stresses of a composite beam design such as Digital Canal's Composite Beam Design. You probably need this type program which calculates more details about the composite beam design than STAADPRO.
Ed
RE: Composite beam in STAAD
Thanks for your help indeed.
I must try this software.
Bill
RE: Composite beam in STAAD
I stumbled on the way to keep axial forces low using MEMBER OFFSET to model composite beams. You need to model the slab in the XY plane with the beams offset using LOCAL command. Be sure to use the correct BETA angle for the right beam orientation. All gravity loads will be in the Z direction.
Edward
RE: Composite beam in STAAD
RE: Composite beam in STAAD
Thanks for your reply and please fogive me if I am late in responding you.
I am not sure if one can specify the member offset distance in conjunction with the beta command. Please see attached pictutre.
LOCAL means that the distances f1, f2, f3 are in the same member coordinate system that would result if the member were not offset and BETA = 0.0
What that means is that when you specify a LOCAL offset, the program is applying those offset values to the unrotated position of the member (BETA=0 position).
What do you think?
Bill
RE: Composite beam in STAAD
Ed
RE: Composite beam in STAAD
Thanks for your help!
I did the same to my model. All axial forces are gone now. Could you please take a look at my modified model see if you find any irregularities in my modified model.
Please not that I used PERFORM ROTATION X 90 to rotate my original model, then I specified the offset distance as shown below:
MEMBER OFFSET
1 TO 20 START LOCAL 0 -0.7 0
1 TO 20 END LOCAL 0 -0.7 0
The BETA is specified as 90 (BETA 90)
Thanks again.
Bill
RE: Composite beam in STAAD
Just change the support at joint 105 to 21.
Ed
RE: Composite beam in STAAD
Thanks for your help.
Could you please say why I have to change the support?
Bill
RE: Composite beam in STAAD
RE: Composite beam in STAAD
Thanks for your helps!
I don't know why we should model the structutre this way.
Don't you think this is a limitation in STAAD?
When you use Digital Canal Composite Beam, do you also get so large axial forces in the girders?
BTW I see you are an advanced user of STAAD using REPEAT in your input file.
Bill
RE: Composite beam in STAAD
I agree that this is a stretch for STAAD. The Digital Canal Composite Beam program is much easier for this problem.
Ed