Steel Deck Diaphragm With Large Openings

[lexeng18]

Hi all,

We frequently design large industrial buildings with steel deck diaphragms. Some of our customers desire to install multiple, very large roof vents to properly ventilate certain production areas. I have been trying to better understand exactly how to properly design the diaphragm for these openings and have found it hard to locate good references on how its done with examples. Best thing I could find is this link below from STRUCTURE magazine's website but just for whatever reason I am finding it hard to follow some of their math and find the explanations lacking:

https://www.structuremag.org/?p=577

Can anyone here either drop some knowledge on me how this is supposed to be done or link to some better source material?

Appreciate any insight.

 

[RattlinBog]

I am by no means an expert on this topic. I found one example in the SDI Diaphragm Design Manual 3rd Ed (attached).

 

[sticksandtriangles]

Terry Malone's book on analysis of irregular shaped diaphragms is a good reference for these sorts of complex diaphragms.

The book is great for understanding complex diaphragm behavior, but way too detailed for practical engineering with tight deadlines and budgets. I would recommend working through some of the simple reentrant corner examples that are provided in the book, they will give you a feel for the things that need to be considered around openings and re-entrant corners.

S&T

 

[lexpatrie]

I guess it depends where you are at in familiarity with the topic. Is this something familiar and the openings are now large, or is the topic relatively new plus the openings.

I thought I saw something (was it in a code) about large openings..... anybody remember that too? You might consider the openings to be large, but the code may not.

This article doesn't seem to have been mentioned yet:

Developing Diaphragm Analysis, Diaphragm analysis, design and connection considerations in steel seismic force-resisting systems, Kennedy, Modern Steel Construction, May 2018

It doesn't deal explicitly with openings, but it's beyond the basic stuff as well.

 

[lexeng18]

I am by no means an expert on this topic. I found one example in the SDI Diaphragm Design Manual 3rd Ed (attached).

This one is great, thank you!

 

[driftLimiter]

This resource has a good demonstration of a series of small openings, I cant remember if it addresses large openigns but the principles are worth understanding.

its also a comprehensive guide for metal roofs which has proven very useful for me.

Link

 

[human909]

I frequently design large multi-storey industrial buildings with steel floors and sheet roof. I generally don't rely at all on the floor or roof diaphragms for these type of buildings at all. My observations of existing buildings of this type designed by others is mostly the same. Clear load paths are provided with structural members either in the floor and/or along column lines.

Sure by ignoring the presence of the steel floor you are over engineering things somewhat. But who knows what future penetrations might be required. These type of buildings (at least in my world) get chopped/changed/expanding often. And a little extra steel bracing in the floor and roof is generally negligible in the scheme of things. (I'm in design and construct so clear cost judgements are always present in my designs.) From my observation North American engineers are more diaphragm focussed than engineers down under.

**Of course there are exceptions. One current structure I currently nearing completion I used the steel floor as a diaphragm. The bay spacing and height to width/length were both smaller than usual. The demand on the diaphragm was low and there were multiple redundancies elsewhere so I modelled it as a stiff diaphragm. (Which I normally do via usual phantom members, so I still know what forces are being transferred)