Flexible Diaphram with Discontinuous Chord

[DrThink]

I am performing remedial repair to an existing steel 1 story building with bar joists and metal deck. Masonry non loadbearing walls for full perimeter. The back wall steps forward and is discontinuous about 10' so the chord is not continuous. The building is 80' x 235' with aspect ratio 3:1. I have about 10kips of tension in this chord.

Is there a standard procedure or detail for resolving the chord discontinuity?

I was thinking putting a diagonal strut to connect the chord forces.

Additionally, the original designer used diaphram action of the roof with no chords. But the joist are supported by a beam line. Would this beam line perform as a chord or do they need a angle chord anchored directly to the deck?

Thanks

 

[DaveAtkins]

Steel beams are excellent chords. Just check the beam end connections (they must transfer the axial chord force in addition to their gravity load reaction), and make sure the chord force can get from the roof deck down into the steel beam (check joist seat rollover).
The notch in the diaphragm is a little more tricky. Can you use just the portion of the diaphragm that is forward of the notch (a 70' deep by 235' long diaphragm)?

DaveAtkins

 

[FalsePrecision]

DR,
I am assuming the beam line bisects the 80' dimension, so the joists span 40'. Since we visualize a horizontal diaphragm as a "beam laid flat", the roof deck being its "web", and the chords (ledger angle or masonry bond beam) being its "flanges", the beam line down the middle produces 2 sub-diaphragms, each with an aspect ratio of 5.9:1
That is no good, so ignore the beam line down the middle.
Next, since you say there is 10k chord tension, I am assuming the 10' notch in the plan occurs midway along the 235' length.
If you have, say, 280 plf shear capacity in your steel deck, you need 2 times 10k divided by 0.28klf = 71' of "drag collector" centered on your 10' notch location. The drag collector can be double angle, or similar. It merely attaches to the underneath of the deck, and its vertical legs are coped at every roof joist it runs over.

 

[DaveAtkins]

I agree with FalsePrecision, except make sure the double angle extends out into the deeper portion of the diaphragm each side of the notch, in order to "drag" the chord force back into the rest of the diaphragm.

DaveAtkins

 

[DrThink]

Thanks for the help