Hilti Profis Diaphragm

[EngDM]

Hey all,

I am playing around with the Profis Diaphragm designer, and I am coming into an issue regarding deflection calculations. I have emailed Hilti about this, but I'm hoping someone here might have a quicker answer since Hilti appears to be on vacation.

To prefice, I have always thought of a diaphragm as a deep beam. By analogy, the equation for diaphram deflection is some form of 5*wl^4/(384EI). In Hilti's documentation here on page 17 (section 6.2) it lists what the variables L and b are (with respect to the deck direction). Since they show L as being dimension perpendicular to deck flutes, that means they take length as your joist length (or plan dimension parallel to joist). However, joists are not necessarily always spanning in the short direction of your overall building (see below screenshots):



Is it not more accurate to list L as your length perpendicular to wind direction, and b as your dimension parallel to wind? Like as far as deflected shape does, the diaphragm doesn't care if the joists are spanning east-west or north-south, the deck is still spanning from my lateral support elements, in this case cross bracing at the end walls.

 

[Greenalleycat]

I don't know anything about the Hilti diaphragm designer, so apologies if I say something dumb
Joist direction often affects the stiffness of the diaphragm in each direction i.e. it is not the same in each direction
I know this is similar to concrete diaphragms with precast floors too
Is that what Hilti is capturing here? They use their L & b notation to represent directions relative to the joists, then apply the loading in each direction once the appropriate properties are calculated

 

[EngDM]

I don't know anything about the Hilti diaphragm designer, so apologies if I say something dumb
Joist direction often affects the stiffness of the diaphragm in each direction i.e. it is not the same in each direction
I know this is similar to concrete diaphragms with precast floors too
Is that what Hilti is capturing here? They use their L & b notation to represent directions relative to the joists, then apply the loading in each direction once the appropriate properties are calculated

thread-16210 (here) says that since the failure is along the 45° plane it doesn't matter the orientation of the deck since it doesn't fail in compression, but rather in shear (based on some Vulcraft information).

In my case my joists are spanning similar to my first sketch above. If I follow their notation, with my L as the short direction I get less deflection than with the long direction as my L.

 

[Greenalleycat]

Maybe someone at Hilti assumed something stupid when they set the software up
Does it come with a manual? Or can you contact someone for tech support?

 

[EngDM]

Maybe someone at Hilti assumed something stupid when they set the software up
Does it come with a manual? Or can you contact someone for tech support?

Manual is linked in a hyperlink in my original post. Their tech support is on holidays until after my deadline

 

[Greenalleycat]

Ah. Well... good luck. I hope someone smarter than me can come and solve your woes

 

[dold]

I see that in the manual they state that "L = length of diaphragm, perpendicular to deck flutes", but typically when using these equations L is defined as the dimension that the wind or seismic load is acting upon. I.e., the length of the deep beam with a uniform load applied along the length.

∆flange = 5qL^4 / 384EI
∆web = WL^2/8bG'

You can see that for flange deflection it does not directly include the depth of the "beam", but moment of inertia of the "flange" (chords) would be calculated using the distance between the "flanges" (chords), i.e., depth of the "beam".

Web deflection directly accounts for the "beam" depth.

Not sure if that's exactly correct but all diaphragm design manuals I've ever seen generally refer to L as the length of the uniformly loaded beam.

 

[ANE91]

Check askhilti.com, in case your specific question has been addressed, there.

I’ve only ever used Profis Diaphragm for strength, to figure out fastener patterns. Never used it for deflections.

https://issuu.com/structuremag/docs/july_2023/10?ff See page 36 of 62 for an explanation of apparent discrepancies in the deflection behavior of metal diaphragms.

https://issuu.com/structuremag/docs/structure-feb22-digital/24?ff Here’s the 3-sided box scenario referenced in the linked thread.

 

[EngDM]

Not sure if that's exactly correct but all diaphragm design manuals I've ever seen generally refer to L as the length of the uniformly loaded beam.

That's what I've always done in the past as well, but you'd think Hilti would have this correct in their manual...