deck uplift 4

[haynewp]

I looked in the Vulcraft deck selection manual and did not see any tables listing the uplift capacity of decking or its attachments. I only found a paragraph stating recommended attachment spacings for up to 30psf uplift. If you have a small building in a very high wind zone (where the diaphragm shear values are small compared to uplift) is there a table published by SDI or other to make sure your deck attachments will hold? Or did I just miss something in Vulcraft?

 

[JAE]

We've encountered this issue as well. What we did was determine the required component wind load uplift on the deck, and then go straight to the fastener tension values to find a fastener capacity. We then determine a density of fasteners to work - such as #12 screws at 24" o.c. We then superimpose this density on top of the fasteners required for shear and voila! we have a design....crude but, I believe, rational.

Deck spot welds can be calculated from formulae given in the UBC Standards for welding light gage to steel.

Power driven fasteners and screws each have published data for pull-out capacities. Be careful, as many of these capacities may be ultimate and you will need to add a safety factor to them.

 

[Ron]

haynewp...my approach is same as JAE's. Consider using weld washers to get a little better weld capacity if you need it. One little "I gotcha" is the tributary area consideration when designing fastening...it is for one fastener influence area, which runs your factor up fairly high, particularly at corner and perimeter conditions.

 

[JAE]

hey...that's right...the corners and edges get a much higher uplift (per ASCE 7) and the tributary area (used to determine your component wind load) is very small so you get a very high uplift force.

 

[samdamon]

haynewp-

Spot weld capacities for various diameters of weld and types of decking metal have been published. I think either United Steel Deck or Nicholas Bouras Industries (A deck supplier) may be able to help you with that part of your question.

It sounds like you are also trying to check the uplift capacity of the deck section. What I usually do is reduce the gross wind uplift by a percentage of the deck/insulation/membrane dead load (In NJ we are allowed to use only 66% of the dead load to reduce uplift, membrane assemblies dont weigh that much anyway, so it hardly matters), and then calculate the resulting bending stresses on the deck, usually assuming that the deck is acting over multiple spans. The Section properties for checking both positive and negative bending should be in your Vulkraft book. (You are checking a suction load, remember, so be careful to use the right Section modulus).