Steel roof deck with bar joists chord force transfer
Steel roof deck with bar joists chord force transfer
(OP)
I have a one story 50' X 86' building with 22 ga type roof deck on steel bar joists at 5'-6" o/c and spanning 50 feet. I designed the metal deck roof deck diaphragm and it can tranfer the lateral loads to the shear walls on each end. My chord force for the diaphragm is 4.2 kips. I am using the steel roof beam at the perimeter of the building to act as the chord member. How do I check the tranfer of the chord forces from the roof deck to the steel bar joists into the steel beam? Can the force be transferred directly from the deck to the joists to the beam (every 5'-6"o/c) or do I need a continuous angle secured to the deck and beam? The roof joists sit on top of the roof beam leaving a 2 1/2" gap between the top of the beam and the bottom of the roof deck.






RE: Steel roof deck with bar joists chord force transfer
What we do is then add a 2 1/2" steel tube between the joists, perhaps every 3rd or 4th joist, to connect the angle to the supporting beam below, thus by-passing the joist seats.
I've seen where some engineers require the joist manufacturer to design the seats to take a certain orthogonal lateral load through their seats but I've not done this too much.
RE: Steel roof deck with bar joists chord force transfer
Provide a 2.5" x 2.5" tube or inverted angle welded to the beam between joists that the deck can get welded to.
Provide angle on top of the joists to weld deck to and then specify required joist rollover resistance to transfer force from top of joist to beam.
RE: Steel roof deck with bar joists chord force transfer
The numbers I have are 1K allowable rollover capacity for a 2 1/2" seat and a 0.5K rollover capacity for a 5" seat.
So you would not technically need the collectors between joists if your service diaphragm shear is <182 PLF (at 5.5' spacing). I guarantee you this is not sufficient capacity in most cases. Still need to add collectors.
RE: Steel roof deck with bar joists chord force transfer
RE: Steel roof deck with bar joists chord force transfer
DaveAtkins
RE: Steel roof deck with bar joists chord force transfer
RE: Steel roof deck with bar joists chord force transfer
Make sure your beam to column connections can transfer the chord force across the connection.