Do I need a collector?

[dcceecy]

I am designing a one-story building as shown in the attached file. the roof slab is reinforced with WWF.

I am wondering if I need a collector member at the dashed line in the skectch. there is a partition CMU wall (12" fully grouted) at that location. Maybe I can design that wall as shear wall instead of adding a collector member below the roof deck.

the building is not in high seismic load area but high wind load area.

the perimeter wall is 12" CMU fully grouted reinforced load-bearing wall. The wall is also designed as shear wall. there are steel columns and beams in the building but now shown in the sketch.
Any suggestions?

 

[msquared48]

The diagram is screaming "Add a Collector Here". Do it.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[msquared48]

In fact, at the re-entrant corner, I would add another collector transverse to the other, in line with the other short shear wall. If you do not do this, you may end up with roofing problems at the re-entrant corner.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[sdz]

What's a collector?

 

[msquared48]

Another term is a "Drag Strut" for a "Collector".

The function is to "collect" or "drag" the lateral shear forces from the diaphragm to shear walls.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Lion06]

I feel like I'm missing something. If there is a shearwall at that location why do you need a drag strut? I would think the drag strut would want to be to the south of the wall, not at the same location as the wall.

 

[OCI]

If there is no collector as shown by the dotted line, how will the small subdiaphram and the upper portion of the large subdiaphram transfer shear into the center wall?

 

[msquared48]

SEIT:

If you have a re-entrant corner on a building, and the two walls stemming from the corner are shear walls, it is a good idea, depending on the size of the rentrant area, to use two drag struts at 90 degrees to each other to break up the diaphragm. Otherwise the diaphragm will have a tendency to tear at the reentrant corner location.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Lion06]

Mike-
Fair enough.

OCI-
I thought the OP said he has a wall that he can use as a shear at the location of the dotted line.

 

[OCI]

StructuralEIT,
Now I understand.

 

[anchorengineer]

Big box huh? Is that a loading dock? I used to design these all the time but it's been a while. You will definitely need a drag strut along the dashed line. Basically the portion of the diaphragm shear along the gap needs to be transfered back to the wall (this wall needs to be reinforced to take the additional load). This load will be a combination of the larger building and the loading dock. You'll need to add more fastening points to transfer this load also.

I assume the bar joists go from front to back and the deep joists from left to right. Your big joist can be your drag strut. (Tell manufacturer to take this load into account when fabricating). You can weld tub steel to the top of the joist in between the bar joists. Place enough deck fasteners to transfer the loads from the side walls into the roof. With a concrete deck you have a decent amount of shear capacity.
I'm sure I'm missing some things. It helps to have someone who's done this before sitting right next to you.

Good luck!
PS if someon has a btter idea I'd be interested.
Thanks

http://www.anchorengineer.com