Diaphragm Connection With Joists
Diaphragm Connection With Joists
(OP)
It is pretty common to have a diaphragm (metal deck or concrete over metal deck) supported by steel joists over structural steel framing. For the case of steel joists spanning perpendicular to collector beams along a frame line, how do you normally assume the lateral load gets from the diaphragm to the steel collector beam, since there is a 2.5" gap (joist seat depth) thru which the lateral force needs to be transferred?






RE: Diaphragm Connection With Joists
We are Virginia Tech
Go HOKIES
RE: Diaphragm Connection With Joists
We are Virginia Tech
Go HOKIES
RE: Diaphragm Connection With Joists
RE: Diaphragm Connection With Joists
When you exceed this capacity, the standard is to provide a 2-1/2" square tube in-between the seats as also referenced my mmillerpe.
RE: Diaphragm Connection With Joists
How do you ensure that the deck flute (which will be parallel to the HSS2.5X2.5) will align such that a puddle weld connection can be made? For example, if the center to center spacing of the flutes is 4 inches (as in the 1.0C metal deck) it seems like there is a good chance the 2.5" wide tube could end up in between two flutes and then a connection can't be made.
RE: Diaphragm Connection With Joists
You're thinking of this in the orthogonal direction; for the case noted, the flutes are perpendicular to the 2.5" tube.
For the case you're thinking of, the supporting member is typically directly supporting the deck.
RE: Diaphragm Connection With Joists
We never said it was easy. You just need to make sure there is a note on your drawing about the required puddle welds. An experienced erector should be able to follow the plans and lay the deck accordingly.
RE: Diaphragm Connection With Joists
RE: Diaphragm Connection With Joists
RE: Diaphragm Connection With Joists
RE: Diaphragm Connection With Joists
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Diaphragm Connection With Joists
Come on... Is anybody doing this? I don't recall ever seeing this suggestion, or ever seeing this rollover force on a set of drawings.
RE: Diaphragm Connection With Joists
From that point on, I reported the value, and if exceeded 1 kip placed "blocking". I would use HSS 2 1/2 x 2 1/2 as well. In the event of the case were the deck flutes ran parralell with the blocking, I would show an "optional" angle welded to the tube to widen the bearing.
RE: Diaphragm Connection With Joists
Has anyone ever had trouble with this getting done correctly in the field?
From what I have seen in workmanship on typical deck installation, I foresee some problems.
RE: Diaphragm Connection With Joists
RE: Diaphragm Connection With Joists
In cases where the joists have a high slope, the bearing seat can sometimes require more than the typical 2 1/2" (see SJI's spec) so we've shown details with a larger tube and noted to "Shim as needed" under the bottom of the tube to match the slope.
We have had some cases where the flutes did not align with the tube below, but as SteelPE mentioned, sometimes corrections need to be made. We have started clearly noting in a detail that the deck is to be attached to the tube and specifying a wider tube if we think it's going to be an issue. We haven't had any problems since.
RE: Diaphragm Connection With Joists
I have been doing this for about 5 years. In fact, this was due to a conversation i had with some engineers from a joist manufacturer. There are rough guidelines on the size of this force for a 2.5" seat (around 5K), and 5" seat (Around 3 kips). When the forces are higher than this, I use blocking between the joists.
RE: Diaphragm Connection With Joists
RE: Diaphragm Connection With Joists
Thanks for the valuable link! However, one thing I noticed on page 35 as you referenced, was that the detail given in Figure 4.2.8 indicates that the number of puddle welds required to transmit the required diaphragm force to the shear collector is per the sidelap fastening requirements.
I'm not sure if I agree with that, because you can technically get a good diaphragm capacity with no sidelap connections. In this case, would no connection to the shear collector at all be adequate?? I don't think so. I would determine the required number of puddle welds based on the pounds/foot force to be transmitted over the length of my collector beams.
Does anyone else require the number of welds to be per the sidelap fastening requirements?