Metal Deck Diaphragm
Metal Deck Diaphragm
(OP)
If I spec a connection pattern for a metal roof deck, what does that mean for the connection between deck and framing parallel to deck flutes. The pattern covers the connection to perpendicular framing, but not sure how to handle parallel framing. Thinking that I need to spec that separately. I've seen someone else specify a pattern in that direction (36/5). Seems like you would just specify a spacing with framing parallel to deck flutes as the pattern (at least as I understand it) wouldn't make sense in that direction.






RE: Metal Deck Diaphragm
RE: Metal Deck Diaphragm
RE: Metal Deck Diaphragm
RE: Metal Deck Diaphragm
RE: Metal Deck Diaphragm
RE: Metal Deck Diaphragm
RE: Metal Deck Diaphragm
I use a bunch of joist and deck framing. The members that frame parallel with the deck flutes would be the supporting girders. In this instance the deck does not attach to the girders as the deck is 2.5" above the girders. The girders are braced by the joists that frame perpendicular to them. In-between the joists I use side lap fasteners in accordance with the diaphragm capacities..... usually with a minimum of 2.
RE: Metal Deck Diaphragm
Thanks.
RE: Metal Deck Diaphragm
If the diaphragm design REQUIRES sidelaps, then you need the same number of connections at the girder to transfer the shear out. You should be installing 2 1/2" tube steel or similar between the joists at their bearing in order to accomplish this.
RE: Metal Deck Diaphragm
RE: Metal Deck Diaphragm
I was taught to follow the publication that structSU10 refers to. If my capacity is greater than the rollover capacity of the typical seat then I will install the 2-1/2" tubes you talk about. It typically happens on very large and heavy building (masonry bearing). You also have the ability to specify the roll over capacity on your drawings and have the joist manufacturer design the seat for this capacity. Beware though, I have seen hundreds of buildings designed by many different companies, and I have maybe seen the rollover capacity specified once.
bpstruct,
If it is a brace frame or a moment frame it doesn't matter. Shear in the diaphragm still needs to come out and into the LFRS (lateral force resisting system). Usually moment frames are longer (take up more bays of the building) than brace frames (which may only take up a few). In either case, if you have a building that is 400' long and you only utilize 100' for the LFRS, you will end up with collector elements that take the shear load out of the diaphragm and drive it into the LFRS. These elements (which can be beams or joist girders) need to account for the axial load from the diaphragm. If you design the system using joist girders then you need to tell the joist girder manufacturer the load the girder needs to resists...... you also need to make accommodations in the design of the connections to accommodate this load as well.
RE: Metal Deck Diaphragm
You have to have the same number of connections at the girder as the sidelaps. Otherwise you are only counting on one screw at at the end of the bar joist to transfer out the shear. Do the math, it does not generally work out. If you use an edge angle instead of tube steel as the shear collector over the braced girder, then rollover usually needs to be considered.
See attached...