SDI Partial Width Expansion Joint and Big Box Warehouses 1

[bsbeng]

I am curious for opinions and thoughts on the Steel Deck Institute’s (SDI) provisions for partial expansion joints presented on sheets AIII-42 and AIII-43 of the Third Edition of the Diaphragm Design Manual (attached). To me, it looks like the intent of this detailing is to provide a flexible interaction between the exterior wall and the diaphragm with the gapped sections absorbing expansion and contraction. As I interpret it, the equations on AIII-43 calculate the required diaphragm shear capacity that allow it to function in this manner without failing the deck connections.
I have a few questions/points of curiosity:

1. How effective is this detail at midspan of relatively long expanses (700 feet) of roof at a typical big box warehouse (metal deck, steel joists and insulated precast wall panels)? It seems to me that it is only effective at the wall/deck interface. Does it have any benefit with respect to deck expansion/contraction that can occur during sunny and hot summer months while the building is being constructed? Won’t the middle section of deck be capable of developing a full 700 feet of accumulated thermal strain creating the issues that an expansion joint was supposed to solve?

2. Are there any limits to the aspect ratio of the b/a? If this becomes too big and the deck appendages too stiff, will this joint even function as an expansion joint?

I have never incorporated this detail before, choosing instead to employ a full width expansion joint in my designs, but this has come up for consideration and I have reservations about how the building will perform during construction if detailed in this manner. I can certainly see the advantages of maintaining a coherent diaphragm, but just can’t wrap my head around how this will behave. Is this detail commonly employed? And if so, is this the correct application for it?

I did submit a question to SDI using their website but have not received an acknowledgment or response.

Thanks in advance for all thoughts and opinions!

 

[lexpatrie]

That just seems extra strength wonky. I don't follow the purpose of that approach. To me you're moving the chord inbound, which increases the force you need to resist, in a larger building, this can already be difficult enough, and it's not dealing with an expansion joint in the middle span of the building either.

Fisher and van de Pas cover expansion joints with metal deck and steel joists in that Vulcraft book.

https://vulcraft.com/Learning/LectureSeries

 

[bsbeng]

Thanks, Lexpatrie! "Extra strength wonky", is a good way to put it! I just can't get my head wrapped around it.

I am still curious about the rationale for this approach and the general behavior of an unjointed building. Like you pointed out, a partial joint increases the demand on the diaphragm chord and does nothing, as I see it, for dealing with movement in the central, unjointed deck. My big concern with these long buildings has been to limit expansion/contraction during construction, which seems to be when it will be the most significant (no insulation, deck exposed to direct sunlight, etc.). Once the insulation is placed and the building enclosed, the magnitude of the expansion/contraction would be less critical, in my mind. With 12' wide precast panels separated by caulk joints, I can't see wall expansion/contraction being a big driver to any issues after construction. Is that how most engineers view this?

A 700ft long unjointed, steel building, for example, subjected to a 70 degree temperature increase, would expand a total of about 3.8" or 1.9" outward in each direction from the center. With a partial joint, how would this amount of potential movement be addressed during construction? Could this result in issues in the end wall panels and their connections?

And, if the cantilevered sections of deck on either side of the partial joint are too stiff, does the partial joint do anything meaningful to mitigate adverse deck/wall interaction?

I am going to keep with my full-joint approach, but I am still curious if my thinking jives with what others consider for these typical precast wall/steel roof warehouses. Am I looking at this correctly?

This topic has always been interesting to me, but I have not found many good references beyond the usual shear transfer details across joints and the standard graph of building lengths to determine when jointing is required. Does anyone have any good suggestions for articles or books that dive more deeply into this?

 

[lexpatrie]

You might be using too large a temperature range there. That'd be my first check, there's a link to the Federal report from back when on expansion joints that gives temperatures for construction and after. If the building is cooled/heated (what about "mildly heated"? like a warehouse?) that shows up.

I don't have anything in the Expansion Joint FAQ that is really spot on regarding concrete walls and steel beam/deck. I mean, steel and concrete expand and contract in a similar order of magnitude but it's not an exact match, but I think the expansion overall is more the concern than differential expansion between the concrete and the steel, particularly if the panels have those big caulked joints in them.

I'd look more to Fisher, though I suppose both sources have "equal authority", I just don't see what they're trying to do with a partial length.

If you find anything super interesting, do tell, or use the feedback in the FAQ and include a link, I could add it to the FAQ, then.

 

[bsbeng]

Again, thanks! I am digging into the National Academy of Sciences article from the FAQ and it gives a good discussion on temperature range to consider during construction. It seems to go a little deeper into the weeds than some of the other articles I've read too.

I certainly will add anything interesting that I come across.