Shear Wall Connection to the Roof Diaphragm

[hardyworld]

Looking for confirmation:

I'm working with an architect on the design of a CMU masonry wall building with a curved steel roof deck and steel joists. The architect intends to have the steel joists bear on their bottom chord so that he can have clerestory windows along the whole length of the bearing wall from the joist bearing elevation to the roof elevation. I know diagonal bridging/cross-bracing is required near the support location, but this detail is not typically intended to transfer loads from the roof diaphragm to the shear wall, is it? I believe that we'll need to install a collector member above the clerestory windows at the roof deck elevation and remove some sections of the windows in his design (replaced with more reinforced CMU wall) to transfer the lateral loads from the roof diaphragm to the shear wall below the joist's bottom chord bearing elevation. Am I correct? Thank you!

 

[jayrod12]

You need to somehow get the load from the roof deck to the wall. Whether it is via bracing or a "perforated shear wall" as you describe is totally up to you. I don't see why you couldn't have the bracing pull double duty unless I'm misunderstanding you talking about cross bracing.

 

[KootK]

Confirmed. You could make the bridging your shear transfer element if you cared to.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[hardyworld]

Thank you. I see no reason to do special design of the cross-bracing at the bearings of the curved joists (which will be special order) so that they can transfer the diaphragm's shear load to the wall at bottom chord bearing elevation. I'll leave those cross members to the manufacturer to design to meet bracing requirements of the joist only. I thought I was correct, just wanted confirmation that those weren't already, by default, designed to transfer shear from the roof diaphragm (I thought it'd be weird if they were).

 

[jayrod12]

Correct. The bridging and bracing provided by the steel joist manufacturer is only designed to brace their roof members and not tranfer overall building shear. Unless you ask them to.

 

[KootK]

See the attached sketch for a possible idea. It would allow for uninterrupted windows and more conventional, top chord bearing joists.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[hokie66]

If the architect is going to expose the roof trusses, he probably doesn't mind another truss along the wall. Diagonals across the windows don't stop the light.

 

[hardyworld]

Thank you for the input everyone! And thanks for the idea KootK. I think I'll try my original idea first and see how the architect responds to that.