Discontinuous Load Path

[Samwise Gamgee]

I am trying to resolve forces in the braced frames on roof. Unfortunately the deck does not have enough capacity to transfer shear over the braced frames, so I have to rely on beams in other bays to act as collector elements. However the beams are not in the same straight line to transfer the load into the braced frames due to stairs in the middle. How do I provide a continuous load path from Beam-2 to Beam-3 and from Beam -3 to Beam-4 ? (Attached a screenshot)

The only other solution is to place side lap fasteners as close as 3" to increase the shear capacity and drag all of that load in the braced frames. But this is very expensive.

 

[KootK]

I'd bet in the end the actual work and load transfer is the same, you're just trading a transfer diaphragm for a hunk of steel.

No, I actually think that your way is better in the way that a shorter, more direct load path is often better. It was wrong of me to suggest otherwise.

 

[KootK]

As long as I check this connection to resist that vertical/axial force, I should be good right ?

Yes although, technically, that force at the tip of your cantilever needs to make it's way all of the way down to the foundation. Granted, much of that load path may not warrant explicit consideration.

 

[jayrod12]

I'd just dump the vertical component at the kinks into the diaphragm which should be adequate to transfer it to the lfrs in the other direction.

 

[Samwise Gamgee]

Thank you so much for all the responses, this is immensely helpful. I had one last question regarding connection between collector elements and the brace frame beam. Are there any special detailing requirements for the connection to transfer both gravity loads and axial thru force. I am just checking the shear tab connection for gravity loads and the axial thru force it will dump into the braced beam. Is that enough ? As long as the connection works, can I rationalize by saying ,it will pass that load directly into the braced beam thru the column ? The collector members pushes the column , which in-turn pushes the force into the braced beam ?

 

[phamENG]

You'll need to check it with the vertical shear from the beam per the load combinations. So there is some overlap. Keep in mind that most shear tabs use short slotted holes to make erection easier, so you'd have to use slip critical connections in those to ensure load transfer parallel to the short slot. Then you've got prying in your angles and beam flange.

 

[BAretired]

The length of roof connected to the braced frames is greater than 79'-6" by the length of the stair shaft. If the 131k wind force includes direct wind and suction, the axial force to be resisted by the sloping edge beam west of Gridline 3 is probably less than or about 70k (tension or compression). Estimating the plan angle to be 10^o, the north-south component is, say 70sin10 = 12k, not a significant shear for the roof deck to resist.

Doesn't appear to be anything to worry about.

BA