Metal Deck Deflection 1

[TDIengineer]

I could use some help on a calculation done for flexible diaphragm deflection.

Given:
1 1/2 x 18 GA deck (vercor). 9'-0" purlin spacing (W14x26) Af = 2.1 sqin
7 welds per sheet, VSC @ 12". R = 1/3

Diaphragm span: L = 42'
Diaphragm depth: d = 56'
Uniform load: w = 612 PLF.

What is the total diaphragm deflection.. I want to make sure I got the right units and I am using "F" appropriately. I got a deflection of just 0.02" at midspan..

Page 6 of 57 of ER-2078P has the deflections equations.

Thanks in advance!

 

[msquared48]

I believe the Steel Deck Institute has or had a manual for calculating just that. I believe I have it at home. I will try to check tonight.

Mike McCann
MMC Engineering

 

[TDIengineer]

oops.. one thing to note. When solving for I for the perimeter flange members assume d is 37.5', not 56'. For the deck depth, it is 56'.
Thanks.

 

[TDIengineer]

Thanks Mike, or you can google the ICC report ER-2078P, page 7 has it.. I think I am crunching it right, and checked my units, but I thought it would be higher, but maybe the span to depth ratio is just about 1:1 maybe it is this small.

 

[TDIengineer]

What horrible proofreading... or lack thereof.. Sorry guys.

 

[wannabeSE]

I assume this is Verco PLB Deck (not Verco's Vercor deck). I calculated 0.018" for the shear. The flexural deflection is probably negligible.

The Steel Deck Institute's Diaphragm Design Manual primarily uses diaphragm rigidity rather than the flexibility factor. If I remember correctly, it has one page with the flexibility factor and it just shows some equations comparing it to the formulas using rigidity. (once you straighten out all of the units embedded in the flexibility factor, G = 1/F).

 

[hokie66]

Do you guys really span 9' with 1.5" deck? When I used to do those type roof decks, we only spanned about 4 or 5 ft.

 

[TDIengineer]

For a roof deck, with a light roof, yes. See it used all the way up to the 10'-0" span limit assuming you're going to get 3 spans of deck.

Thanks Wannabe. Yes, The PLB using the mechanical sidelap fastener but puddle welds at the supports.

 

[XR250]

Max. construction span for 1.5" B deck is 9'-1" - so you are pushing it (assuming the deck you are using is similar)

 

[hokie66]

Too bouncy for my liking.

 

[johnbridge231]

Eurocode 3, Part 1-3 provides details on such calculations as well.

Analysis and Design of arbitrary cross sections
Reinforcement design to all major codes
Moment Curvature analysis

http://www.engissol.com/cross-section-analysis-design.html

 

[TDIengineer]

Here is the load table I am using.. Superimposed DL to the deck is less than 20 psf dead + 20 psf live = 40 total

Curious to see where you got 9'-1".

 

[TDIengineer]

And yes, the PLB by Verco.. Not Verco. Triple span condition.

 

[XR250]

9'-1" came from the Vulcraft Catalog under construction loads (not in-service loads)

 

[hokie66]

Construction loads on metal deck are often the controlling criteria. Walking on 1.5" deck spanning 9' before it is connected, 3 span or not, is tricky.

 

[abusementpark]

Your diaphragm depth is greater than the span. I'm not surprised the deflection is small.

I wouldn't even worry about diaphragm deflection until you get to at least a 1.5 to 2 aspect ratio.