Diaphragm design.

[SteelPE]

I have a building that has an odd shape. Basically it I end up with a bunch of joist that splay from a common radius point. The joists are around 96’ long at a maximum the joists are 13’ apart and at a minimum they are 2’-0” apart. I have brace walls and bearing walls about the building to act as a LFRS for the structure.

In order to get the decking to work, I have to use a 3” deck. However, when it comes to shear resistance the 3” deck is not that great. I need to develop some rather large shear loads on the side of the building were the joists are 2’ apart (around 500plg). Looking in the SDI diaphragm design manual I see that the minimum spacing of supporting members is 10’-0” for my case (18ga deck). With this I can develop an allowable shear of 530 plf for seismic loads. This is using 13 sidelap screws.

Since my spacing of my joists are only going to be about 2’0” o.c I am thinking about putting a note on the drawing limiting the spacing of sidelap screws to 9” o.c. ({10 ft x 12 in/ft}/13 SLS = 9" o.c.) to mimic what is shown in the manual. Does this seem like a reasonable approach to achieve my requirements given no data in the Design Manual?

 

[BAretired]

Maybe it would be more economical to reduce the number of 96' long joists, span smaller joists between them at, say 6' centers and use 1.5" deck running radially.

A plan would help.

BA

 

[slickdeals]

I would suggest running it in the Hilti Profis Diaphragm program. That will allow you to use many different criteria (deck type, span, fastener pattern etc. etc.). It is a free download as well.

 

[SteelPE]

BAretired,

The architect kind of likes the current plan so changing the framing would not be advised.

slickdeals,

I will look into that, does it check the design for normal anchors or just Hilti. I am looking to do the standard 5/8" dia puddle welds with #10 tek screws for SLF.

 

[BAretired]

SteelPE,

Too bad because four girder trusses, one at each column looks like an idea worth exploring.

BA

 

[SteelPE]

Not really my call. I just have to make the decision between a horizontal roof truss or a metal roof diaphragm.

The roof truss is going to be difficult to construct which is why I like the metal diaphragm idea better. I am thinking about using 16ga material instead of the 18ga I was considering before.

Regardless, is my initial idea sound?

 

[abusementpark]

Try Verco decking. They have some high-strength deck options.