Composite steel floor girder with noncomposite floor beams

[jpw2913]

Can composite steel floor girders be used with noncomposite steel floor beams? I guess my question is, does the whole system have to be composite construction, or can just the girders be composite? Obviously, all of the decking will be composite deck. Thanks for any info!

 

[r13]

Yes. If the system is satisfactory for one way action, why provide two way support mechanism. You have to weigh the cost of one way vs two way construction though.

 

[Agent666]

I'm not sure what this has to do with one way or two way construction as per r13's reply as that seems like the answer to a completely different question. The question wasn't about this unless I'm missing something obvious.


But yes with respect to mixing and matching you can mix and match provided you take appropriate consideration of the different strength and deflection criteria and differences in mechanisms at play (for example creep and shrinkage deflections in composite construction). Often for example you may not be able to get sufficient studs on the beams to achieve the required degree of composite action to satisfy minimum requirements from codes, so you are forced for example to design for non-composite whether it's beams or girders.

 

[r13]

Can composite steel floor girders be used with noncomposite steel floor beams?

For the question, the short answer is a absolute YES.

If you make girder and transverse beams all composite, you have achieved a grid system, for which, with the loading the same, the members can be smaller, and deflection is less, compared to the girder only option. So the main difference here is which way is more economical (if no head room problem), you either pay for the bigger size of the girder, or pay for the studs.

 

[Boof19]

(for example creep and shrinkage deflections in composite construction).

Do you typically check creep on composite floor systems? Months ago I asked one of the engineers I work under if it was something I need to be concerned about and he said it's negligible. Not saying it doesn't exist, but I'm honestly curious if any of you out there are checking this?

 

[Agent666]

Creep and shrinkage could add 10-20% of deflection over time to a well proportioned composite beam design, so round these parts we most definitely consider it for longer term deflection cases.

Shrinkage deflection is usually more than creep though, creep might be 1-2mm say, then shrinkage might be 5-6mm to show the relative proportions of it. For propped construction creep is generally higher as the permanent loads being supported that contribute to creep are higher than in unpropped construction where the self weight of the slab is not supported by the final composite section. For higher shrinkage concretes, shrinkage deflections increase accordingly.

 

[r13]

Boof19,

Creep is a serviceability problem that rarely checked in typical floor system. It is necessary when supporting heavy equipment that require precision in vertical alignment with time.