Bar Grating as a Diaphragm

[dcarr82775]

I found an old post on this from 2004, but thought I would see if there is anything new on it.

I have a project in an existing building where near as I can figure the bar grating is the diaphragm. 2"x3/16" bars @ 1 3/16" o.c. with little twisted cross bars at 4". I would never chose to use bar grating for a diaphragm, but I don't have much of a choice here. Anyone have info on using bar grating as a diaphragm? McNichols is no help

 

[weab]

Assuming that bearing bars span from top flange to top flange and every so many bars are welded to the flanges, then this can be used for top flange bracing only.

Diaphragm forces longitudinal to the beams stay within the beam as axial forces to the supporting girders. I would suggest that you will likely need to design your girders for weak axis bending.

I guess that if you designed the bar welds to carry the beam transverse loads, then you can count the grating to carry this load to the beams on the column rows. I would not characterize this as diaphragm action. If anyone is aware of research that can quantify grating diapragm action, I'd like to hear it.

 

[jrmack]

If we are talking about 6 m or 20 feet, welding it down will act as some form of diaphram for a platform. This could stablilze the members supporting the platform (lateral torsional buckling), but beyond that you got to brace things.

 

[asixth]

I don't have solid technical information to back my claim, but I have never considered bar grating as a diaphram or to laterally restrain the top flange which it fixes to.

 

[graybeach]

Bar grating doesn't have much resistance to in plane deformation. By this I mean that a rectangle of it could easily become a parallelogram. Therefore it should not be considered to be a diaphragm.

 

[steve1]

According to these guys (see question #27)

http://www.unistrut.com/DB/PDF1/Grating_FAQ.pdf

their grating can be used for a diaphragm.

I am not endorsing this use but simply pointing it out.

 

[slickdeals]

Can a Bar Grating welded to a compression flange be used as a brace?

Assuming there are C-Shaped joists every 4' o.c. over a 125' width. The 3' wide - 1" x 1/8" bar grating is welded to the compression flange at 3 locations along its width. The bar grating is not terminating into anything that will brace it.

My argument is that for a global lateral buckling of all the flanges will happen only during an unlikely event of the entire floor being loaded with the assumed 100 psf. The loading on the joists will almost be on a few joists at a time, with the other joists not being loaded at all.

Can these joists (which don't displace laterally due to load) be used to brace the compression flange of the beams that are loaded?

Thoughts?

We are Virginia Tech
Go HOKIES

 

[paddingtongreen]

To prevent elastic buckling, you only have to restrict rotation or translation of the top flange.

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

 

[msquared48]

The 2" X 3/16" vertical bars, if properly welded to the top flange of the supporting members should serve to restrain the top flange, but I would not rely on any diaphragm action.

I would seriously consider welding diagonal flat bar to the bottom of the grating to transfer any lateral forces, making connections as appropriate for your load conditions.

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

 

[abusementpark]

I would think that bar grating (if properly welded to supports) could act to brace the top flange of a beam.

I'd be a lot more hesitant to rely on it for any diaphragm action, except for very low load levels. I suspect that it does have a somewhat substantial diaphragm capacity, but there needs to be a rigorous testing program to prove it and develop design guidelines for practitioners.

 

[slickdeals]

Thanks fellas. It would seem that the entire floor would have to get loaded simultaneously to induce a lateral translation of all the compression flanges.

That brings another question. Are there any requirements for sway loads in interior mezzanines. For example, if there is a 100' x 100' interior mezzanine in a building corner, what kind of lateral forces (if any) are you required to design. I skimmed the code to see if there were any minimum sway forces, but came up short. The only sway forces I found was for stadium seating in a direction parallel to the span.

We are Virginia Tech
Go HOKIES