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OVERLAPPING MEMBERS...NEED HELP
5

OVERLAPPING MEMBERS...NEED HELP

OVERLAPPING MEMBERS...NEED HELP

(OP)
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.

RE: OVERLAPPING MEMBERS...NEED HELP

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

RE: OVERLAPPING MEMBERS...NEED HELP

(OP)
@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.

RE: OVERLAPPING MEMBERS...NEED HELP

(OP)
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.

RE: OVERLAPPING MEMBERS...NEED HELP

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.

RE: OVERLAPPING MEMBERS...NEED HELP

(OP)
^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.

RE: OVERLAPPING MEMBERS...NEED HELP

(OP)
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.

RE: OVERLAPPING MEMBERS...NEED HELP

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

RE: OVERLAPPING MEMBERS...NEED HELP

(OP)
^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.

RE: OVERLAPPING MEMBERS...NEED HELP

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

RE: OVERLAPPING MEMBERS...NEED HELP

(OP)
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.

RE: OVERLAPPING MEMBERS...NEED HELP

I would use the member centerlines in the model.

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

RE: OVERLAPPING MEMBERS...NEED HELP

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

RE: OVERLAPPING MEMBERS...NEED HELP

(OP)
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.

RE: OVERLAPPING MEMBERS...NEED HELP

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

RE: OVERLAPPING MEMBERS...NEED HELP

(OP)
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)

RE: OVERLAPPING MEMBERS...NEED HELP

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

RE: OVERLAPPING MEMBERS...NEED HELP

(OP)
@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.

RE: OVERLAPPING MEMBERS...NEED HELP

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.

RE: OVERLAPPING MEMBERS...NEED HELP

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

RE: OVERLAPPING MEMBERS...NEED HELP

Glad to be of help.  Good luck.

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

RE: OVERLAPPING MEMBERS...NEED HELP

(OP)
@Sir Ron thanks!!!

RE: OVERLAPPING MEMBERS...NEED HELP

No problem!  Good Luck.

RE: OVERLAPPING MEMBERS...NEED HELP

Glad to see that Ron and Mike have helped with your problem, but I am still not convinced that they have addressed the right problem.  When you said the bottom chord of the steel truss is restrained by "wrapped dowels", I took that to mean the dowels are for horizontal bracing only, not for vertical load sharing.  A detail would help to show the intent.

RE: OVERLAPPING MEMBERS...NEED HELP

I've been thinking that too, hokie. I'm trying to imagine a truss that cannot deflect because the bottom chord is in contact with a wall, continuously?or at intervals?

Michael.
Timing has a lot to do with the outcome of a rain dance.

RE: OVERLAPPING MEMBERS...NEED HELP

OK...  I can see thaat scenario.

The dowels, at 4'-6" OC, if they slip up and down within the concrete beam, and being welded to the truss, may be solely for lateral support of the bottom flange of the truss...  

If the vertical deflection of the truss, however, exceeds the vertical slip capacity of the concrete beam connection, whatever it is, then a vertical load could be imparted to the concrete beam.  

In all likelihood, at the 4'-6" spacing, a measurable degree of composite action may be a pipe dream.  As mentioned, a good detail of the connection would answer a lot of questions.

I had previously envisioned these dowels as embedded in the concrete beam and welded to the truss.

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

RE: OVERLAPPING MEMBERS...NEED HELP

When I see a comment like;
'the truss is deflecting with the beam I can see from its behavior that it's acting as part of the beam. Well I think I just have to move it away...and revise their plans. Lots of work though',  
it's obvious that you need the advice of an experienced supervisor.

Asking questions on a forum is not the best place to get that advice.

RE: OVERLAPPING MEMBERS...NEED HELP

(OP)
@Sir Apsix, msquared48 envisioned it correctly.

I encountered some errors so I need to find a solution, that's why I'm hoping for some relevant technical answers so I can weigh, check and apply it to the problem accordingly. I'm very thankful to some members who shared their opinions relevant to the matter in hand.

Contrary to your opinion, I find forums very helpful, you can get lots of great ideas although, there are some irrelevant and unnecessary comments, but generally, seeking advice inside open forums is still one of the best way to find the answer/s that you're looking for.

One more thing, I don't think my experienced supervisor will be happy to help me with some part time jobs after my work in the office.

To the members who took some time to share their ideas addressing my queries, I'm very thankful to you guys. And to those who did otherwise, maybe next time you can at least just try to extend some help.

RE: OVERLAPPING MEMBERS...NEED HELP

engrbon
I was just a bit concerned that you apparently contemplated changing the building plans because you couldn't model it in your analysis software. That's the tail wagging the dog.

I'm not trying to steer you away from using the forum, I've learnt a lot here and I'm sure you can too.
As for 'unnecessary comments'; they come with the territory, whether you appreciate them or not.

RE: OVERLAPPING MEMBERS...NEED HELP

If you are modeling two members, which have different centers of gravity/inertia, you should be modeling them as separate members, connected at intervals.  Model the connections using notional connecting members - in RISA 3D there is a way to specific way slave these together with infinitely stiff & strong connections.  In other software, you would create a series of stiff connecting members.

Otherwise, determine the properties of the composite member and model it as a single member using these properties.

It sounds like you may be doing work outside of your expertise without supervision by a licensed structural engineer, which none of us here would recommend, and most place in the US prohibit.

RE: OVERLAPPING MEMBERS...NEED HELP

(OP)
@Apsix, please accept my apologies. Thanks.

@TXStructural, Thanks. Just wanted to try the software, I want to learn more that's why I'm asking, if others are ashamed to ask because other people might think that they don't know anything, count me out. I will ask if something confuses me. I not only use all the brains that I have, but all that I can borrow. That is the reason why I'm here to learn from experts like you. Thanks again for the input I will look into it. As for now, I'll wait and see, all the documents and plans are with the building officials for approval. One more thing, nothing to worry, I have my own professional license and legally allowed by law to practice.

@Everyone, Thanks for all the valuable comments, you are my expert supervisors.  

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