Retrofit Steel Deck to CMU Wall Drag Struts

[Hipmetal]

A common scenario I run into here in Indiana: Customer has a single story rectangular building with 4 CMU shearwalls (2 loadbearing, 2 non-loadbearing), steel roof bar joists, and standard 1.5" metal decking. Customer asks us to knock some big openings in one or more of the shear walls. I go do a field investigation and realize there are no drag struts connecting the roof diaphragm to any of the 4 walls (more common than not in buildings I encounter). Since I'm modifying a shear wall I feel like I am taking on responsibility for the entire horizontal force resisting system of the building. Assuming that I can justify adding the requested openings (preferably with empirical design if possible) I'll need to at least add drag struts to the 2 non-loadbearing walls. The loadbearing walls are connected to the diaphragm via embed plates welded to the bar joist, so I at least have some connection on those walls even if it relies on the joist seat not rolling over. The loadbearing walls are usually longer and have lower distributed shear loads also.

The simplest method I've come up with for retrofitting a drag strut is using a cold-formed piece of angle, maybe 16ga, installed on the underside of the deck against the CMU wall. Sheet metal screws installed from below connect the metal decking to the angle at every low rib. Self-tapping concrete anchors connect the angle to the CMU.

-Does anyone have any better solutions for this scenario?
-Is this omission in the original building construction as common everywhere else as it is here?
-Would you require the customer to install drag struts on the loadbearing walls regardless of the distributed shear loading on those walls?

Thanks

 

[XR250]

I would not think adding openings in the shearwalls will affect the path of the load getting to the top of the wall. Is it prudent for you to take care of it? - probably. But, you might want to run it by the owner.
I run into this same condition in many older buildings.
How are the out-of-plane loads on the side walls currently resisted?

 

[skeletron]

1. The bent plate with screws is fairly common from what I've seen in my review of the literature. Either that or a continuous angle.

2. I have seen some pretty suspect CMU/URM construction over the years. I think for single-story buildings it *waves hand* works. But I'm not convinced that it meets the expectations of the current Code.

3a. Yes, I would add the drag struts on the loadbearing walls (assuming these are referenced as the OWSJ with welded embed plate) mainly because you are affecting the current LFRS in that direction. My line of thinking is that you are affecting the capacity chain (ie. the walls) somewhere in the mid-section, so I would feel it was necessary to look at the whole chain as part of my scope.

3b. In terms of adding drag struts all the way around: yeah, that would be nice. But it really should be brought up to the owner first. Sort of along the lines of "voluntary upgrades". Make them aware that it's probably a good time to upgrade now, and likely cheaper. I think you may open a can of worms, though, depending on its existing design.