OVERLAPPING MEMBERS...NEED HELP 5

[engrbon]

Hi guys I've been trying to use a software to model a steel truss where the bottom chord is on top of a concrete beam along its full length. I was able to create the model but the program is issuing a warning message saying that the members are overlapping. Will this affect the analysis and design of the whole structure? Thank you.

 

[connectegr]

Does the concrete beam act as part of the truss? Are they in direct contact? What happens when the truss deflects? Why put a truss on top of a beam?

http://www.FerrellEngineering.com

 

[engrbon]

@connectegr,

The actual structure will be like that sir as per plan so I've been trying to model the whole structure according to the plan. Yes the whole bottom chord is on top of the beam and columns at both ends. The bottom chord of the steel truss is only restrained by dowels wrapped & welded to the bottom chord at 1.5m on center. I used to transfer the truss loads to the beams but now I tried modeling the whole structure including the steel trusses and I encountered this error. Any solution in mind sir? thanks for the reply.

 

[engrbon]

Looking at the way the model moves the truss is deflecting with the beam I can see from it's behavior that its acting as part of the beam. Well I think I just have to move it away...and revise their plans. Lots of work though.

 

[hokie66]

Your description does not give enough information to comment. I am imagining a concrete beam which is part of a wall system and perhaps the lateral resisting system, while the truss sounds like it is a roof truss subject to uplift, thus the need to restrain the bottom flange. Am I warm? What's the software for? If you don't know how the structure behaves, using software to analyze it is dangerous.

 

[engrbon]

^Well i just tried using the program sir...the structure is a moment resisting concrete frame with roof trusses.The structure is subjected to DL, SIDL, LL, WL & EQL. Just hoping if anyone can give me ideas about the error I encountered. I just moved all the trusses away from the beam and no more warning errors. Thanks.

 

[engrbon]

I tried to create the whole structure in one model hoping to make it a li'l more easy so i' don't have to transfer loads manually. It just happened that the plan they provided looks like this so I tried to see how the model will behave.I think it's my first time to ask for suggestion in this form...I'll get used to it. I just wanna learn more from you guys. Thanks.

 

[msquared48]

From your description here, it seems like the welded dowels are an attempt to make the truss at least partially composite with the concrete beam.

You might have to look at the problem from this perspective and try to model it as one composite bottom chord of the truss, partial or otherwise...

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[engrbon]

^Thanks for the info sir I don't think they are thinking about it when they drew the plans... Well I might also consider putting base plates at both ends of the trusses to elevate the trusses from the beams considering of course the maximum deflection of the trusses & beams. So no need for the dowels. Going back to my main question sir regarding overlapping in the model, is there a way to separate objects if they are at the same plane and exactly at the same location? (just an hypothetical question just curious) Thanks.

 

[msquared48]

Hard to imagine them being at the same exact location.

Are not the centerline of the concrete beam and the centerline of the truss bottom chord member separated by a definable vertical distance?

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[engrbon]

Well what I did is move the insertion point of the concrete beam on its top center to so that when I look at the extruded view it is almost depicting the same position as what they indicated in their drawings.I did not put any gap between the two objects to see the behavior of the structure because the plan they gave shows that the bottom chord is lying on the full length of the beam.

 

[msquared48]

I would use the member centerlines in the model.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Ron]

Have you tried modeling the truss separately, but pin supported at each dowel? Otherwise treat as msquared48 suggested...composite section.

 

[engrbon]

I tried that already sir it's just that I'm looking at the possibilities of minimizing labor 'coz I need to transfer the load reactions manually. Thanks.

 

[Ron]

That should not be a problem...the truss reactions get transferred manually to the concrete beam.

 

[engrbon]

Thanks a lot guys your such a big help. I'll try making separate planes using their centerlines and see the result but where am I going to put the restraints? And how will the load transfer. (Sorry for this questions hope you can bear with me. Thanks)

 

[msquared48]

That would work. And if you want it more precise, calculate the deflection of the concrete beam at the dowell points, and reapply these "support settlements" to the truss to get revised truss loads.

You could itterate this procedure as many times as you needed to bracket the solution you seek.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[engrbon]

@Sir Ron

Sorry If I didn't get your point with your last comment. If I'm going to make a separate model for the truss with pin connections to depict the dowels, what do you mean by the truss reactions get transferred manually to the beam? Or are you saying that I'll transfer them manually or if there is an option in the program to transfer loads to another model. Thanks.

 

[Ron]

The restraints are the dowel points; however, depending on the analysis program you are using, you might have to specify that a reaction will be calculated at the restraint. Once the truss support reactions are determined, then apply those manually to the concrete beam. The dowels create no restraint for the beam, so just apply them as point loads along the beam.

 

[engrbon]

@Sir msquared48 thanks I got your idea. This forum is really great!!!