Fastening Steel Deck Alternatives

[GC_Hopi]

How are people handling substitution request for deck fastening to open web joists? Is the contractor/third party engineer requesting the substitution responsible for checking strength, stiffness, base material thickness and does this need to be sealed or should the EOR include this re-design effort in the submittal review? Curious to see what others.

 

[jayrod12]

In our office we specify our preferred method, but indicate that sealed shop drawings for alternative fastening methods are acceptable provided the strength and stiffness of the original design is met or exceeded. Further we indicate that the fastening method must be coordinated with the steel joist supplier to ensure it meets their requirements.

Sometimes it's a fight to get those things, other times it's not a problem.

 

[BAretired]

So what are we talking about, welding versus screwing? Those are the only methods I can think of.

 

[canwesteng]

HILTI has a powder actuated fastening as well

 

[Deadblow]

We have started showing two options on our plans. We usually show options for welding, screwing, or pneumatic pinning.

EIT

 

[driftLimiter]

The fastener type has a pretty significant effect on the diaphragm behavior. Unless the various options were considered in design I would think at very least a 're design' of the diaphragm is needed. I'd have to bill for that time.

 

[Aesur]

Typically we use welded connections and tell them if they want a substitution they need to submit a sealed letter and supporting documentation showing the substitution is equal or better. Usually this works, a few times it didn't.

@Driftlimiter - out of curiosity, how many designs have you seen that actually did more than check the shear capacity and chords of the diaphragm for steel deck..

 

[dold]

@Driftlimiter - out of curiosity, how many designs have you seen that actually did more than check the shear capacity and chords of the diaphragm for steel deck..

I'm not drift but where I've worked we always checked diaphragm strength as well as deflection. Specifically for large tilt up warehouses in high seismic regions. Big 400'+ spans can really move around a lot and warrant as stiff a diaphragm as you can get. Keeping ASCE stability coefficients in check is pretty important otherwise you start having to look at P-delta stuff. E.g. diaphragm moves a lot then you get walls starting to lean over on the diaphragm and columns pushing on the diaphragm in a vicious cycle.

Different firms spec fasteners differently of course. One place I worked we'd give them options for puddle welds, PAFs, and screws, as well as options for different sidelaps: PunchLok, welded, or screwed. Sounds tedious but we put together a handy spreadsheet to give all equivalent fastening methods for strength and stiffness.

Other firms we'd spec one and if they requested something else we'd bill for the substitution request. Sometimes the contractor would just spit out a hilti report from whatever their diaphragm program is called. I think you punch in a spec'd fastening method and hilti 'profis diaphragm' would provide an 'equivalent' hilti fastening method.

In my experience the PAFs are definitely the fastest to install, and they eliminate a lot of issues with welding such as welders burning the hell out of top chords of joists.

 

[driftLimiter]

@Driftlimiter - out of curiosity, how many designs have you seen that actually did more than check the shear capacity and chords of the diaphragm for steel deck..

Like dold says I try to always check shear, chords, deflection stability coeff. Tiltups are very demanding on the diaphragm in my region so these checks are relevant. Of course certain limits generally control (shear & chords). How about panel uplift resistance, even if the fasteners have more shear capacity does that mean they have more uplift capacity as well?

My original point was actually mostly related to shear. If you simply change the fasteners and keep other factors the same, the diaphragm shear can be affected. Maybe its as simple as checking the shear capacity of the individual fastener....

What I am saying is that I would want to re-perform all the related checks on the diaphragm if someone asked me to substitute fasteners.

 

[lexpatrie]

Oh how I wish people wouldn't put options into their sealed plans. How exactly am I supposed to determine, after it's constructed, how it was done in twenty years in the unlikely event the structural drawings somehow survive?

 

[XR250]

PAF's don't always work well on BJ's with thin flanges. I have heard stories from the field that they don't penetrate because they are too flexible.