Decking to Steel Beam - Laterally Braced? 1

[Teguci]

non-composite concrete slab over steel decking is puddle welded to a steel beam. Is this steel beam laterally braced by the puddle welds to the decking?

Concerns:
- Puddle welds failing due to beam bending
- Any code issues/documentation?

Are the puddle welds needed for lateral bracing? (Don't think I will design this way even if you guys say yes)

 

[Lion06]

I would say yes. I would typically consider roof decking with the flutes perpendicular to the beam as bracing the beam, so why not with a floor. I also believe that the concrete eliminates any concern of the flute orientation.

 

[ChipB]

If a concrete slab poured using metal form deck which is in turn welded to the beam, doesn't brace the beam's flange, I have completely f'ed up a whole bunch of designs through the years. But then again, if that's the case, I'm not alone in this boat!

It's braced as long as it is connected to the compression flange. I say this b/c I know someone out there is going to point out wind uplift on a roof if I don't!

 

[Ron]

Yes, it is braced. I would make sure the puddle welds are inspected and that they are done correctly. I rarely see them done right the first time....remember a puddle weld is one of only a few welds where reinforcing not only counts, but is required.

 

[Teguci]

Isn't there a concern that shear would break the puddle welds when the beam flexes? (The whole VQ/I shear interaction issue)
Or, the decking with concrete is considered flexible enough to allow some "bunching" at the welds?

 

[enginerding]

If the deflection of the beam breaks your welds, your deck diaphragm is pretty much screwed as it is.

 

[bdSE]

Here's how you can satisfy your question by use of the code.
AISC - Steel Construction Manual - Edition 13 (black book)

Turn to Appendix 6 just before the commentary section.
6.3.1a - Equation (A-6-5)

Lateral Bracing
Bracing shall be attached near the compression flange...
The required brace strength is...

Pbr = 0.008 Mr Cd / ho = (kips)
0.008 (unitless)
Mr (k-in)
Cd (unitless)
ho (inches)

Then it goes on in the next equation to describe the required brace stiffness.

Anyway, with a little effort you should be able to feel better or immeasurably worse about your previous designs.

Try this calc on any wide flange holding up the first floor of a wood frame building (like your home perhaps)and notice that the lateral bracing comes from little nails bent around the top flange of the beam. Yikes! Unless they took the effort to shoot a plate with PAFs and sufficiently toe nail the joists there are many under designed beams in homes around the country.

 

[rowingengineer]

I find comfort in the fact that the flange of the beam due to the weight of the deck above cannot twist or buckle easily.

However I would have thought it would be cost efficient to make this a composite beam and use shear studs, at least that is the common practice around my town.

When in doubt, just take the next small step.

 

[msquared48]

If the decking is a form deck that can rust out with time in certain circumstances, I would say no. I have seen that happen on more than one occasion, being called in afdter the fact to make repairs. I would also say no as many of these are 26 gage or higher, making weldability of the puddle welds an issue.

However, if the gage is 22 or lower and 1.5" in depth, no problem. Depending on the manufacturer, you may need to spec weld clips though to make it work.

Mike McCann
MMC Engineering

 

[rowingengineer]

Mike,
The bearer to deck situation where they external or internal environments? if internal was this a high humidity environment thus galvanitic corrosion was possible?


When in doubt, just take the next small step.

 

[msquared48]

They were exterior, one a set of stairs, and one a slab over a garage - waterproofing issue.

Mike McCann
MMC Engineering