Can I rely on checker plate to be a diaphragm?

[GalileoG]

For a 3 foot wide platform, I see little reason why a floor plate can not be used as a diaphragm as long as the floor plate is properly anchored to the supporting steel. Adding horizontal bracing seems rather redundant. Second thoughts?

 

[thaidavid40]

For 3'-wide and 8'-long span, I tend to agree with you. For 3'-wide and 40'-long span, we would typically add some diagonal struts.
Dave

Thaidavid

 

[spats]

I would generally not do it. On a related matter, I generally don't even like to use it for lateral support of beam top flanges. I never use grating for lateral support.

 

[XR250]

For 3'-wide and 8'-long span, I tend to agree with you. For 3'-wide and 40'-long span, we would typically add some diagonal struts.

If it is welded properly and had some chords, I imagine it would be plenty stiff for even 40' x 3'.

 

[KootK]

With adequate and reliable fastening, and checks for shear buckling etc, I'd think the checker plate a worthy diaphragm. That said, the strategy probably doesn't play particularly well with typical industrial design philosophy which places a high premium on:

1) redundancy;
2) transparent load paths and;
3) the pragmatic consideration of future modifications.

Will you have transverse framing at the joints between checker plate panels?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[GalileoG]

Thanks for the response.

I was not planning on specifying framing at the joints - I feel that framing at the joints makes for a better diaphragm action, but even that seems redundant.

Now with that said, this 3' wide platform turns to a stair along its length and steps 8 feet vertically (the channel is cranked and continuous). Leaning towards providing horizontal bracing just because there are stairs. Thoughts?

 

[spats]

Provide horizontal bracing in any instance. Most people would not consider checker plate to be lateral bracing in a structural system. If you don't treat it as such, the details will be overlooked. It would need to be subject to inspection.

 

[KootK]

I was not planning on specifying framing at the joints - I feel that framing at the joints makes for a better diaphragm action, but even that seems redundant.

I don't disagree. However, it changes a couple of things:

1) Shear buckling capacity and;
2) Instead of just VQ/It forces, you'll need to move 100%V in and out of the beam flanges at the joints. Not that that can't probably be accomplished with a tiny bit of welding anyhow.

Now with that said, this 3' wide platform turns to a stair along its length and steps 8 feet vertically (the channel is cranked and continuous). Leaning towards providing horizontal bracing just because there are stairs. Thoughts?

A closed riser system can also be a pretty stout diaphragm. I'd still apply the same three arguments that I mentioned above of course.

If you'r especially concerned about the stair, you could go hybrid. Just throw in some transverse framing at the top and bottom of the stair and switch to discrete bracing in between.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[dhengr]

GalileoG:
Why is the 3' wide (high?) checkered pl. any different than the web in a light plate girder? 3' by 4, 6 or 8' long web panels are probably reasonable web panel proportions. You can order the checkered pl. in any of these lengths. I would put an down turned 2x2" angle at each joint and use it as a backer bar to weld two lengths of pl. together. Obviously, your pl. girder is laying on its side instead of standing upright, and we don’t know the actual loads or other particulars. Otherwise, I’d look at it as a light pl. girder design, and you might have to adjust the spacing of the web stiffeners as a function of the web pl. thick. and your actual loads. You’ll need a toe board on the walkway, so use a deep enough channel or std. bm. so 4" of the two side sills stick up above the checker pl. If you can use a channel, turn the flgs. out so as to simplify welding of the checker pl. and the stiffeners to the side sills (girder flgs.). You’ll likely need some concentrated lateral support at the t&b of the stairs, and several other locations to pick up the diaphragm (pl. girder) reactions. The handrails are of a std. pipe design.

 

[TLHS]

I'm sure it can, but I wouldn't do it. Someone's going to come along and cut that thing open for equipment access or something one day.

Also, I've generally moved away from lateral bracing whenever I can. I treat members as unsupported for LTB and take lateral force in weak axis bending. Except in large cases it doesn't affect the steel size much and you save all the screwing around installing the bracing. Plus, bracing is usually hugely oversized for practical reasons, so you can end up saving steel some of the time.

Obviously there are times when bracing is the way to go, though.