ligth gage metal tearout at connections 5

[PSUengineer1]

Please reference attached photographs. A cove detail constructed of light gage metal is fallen to ground. The connection of the vertical metal studs to the horizontal track is achieved with metal screws visible only on one of the horizontal track's flanges. The edge distance of the connection looks terribly close to the edge of the track's flange. Are there references out there for minimum edge distance at this type of connection? I checked with Dietrich and they have no typical details. I cannot get my hands on the light gage shops.

The horizontal track was attached to wood trusses above via wood blocking. The horizontal track at top of light gage cove detail wall appears to have been installed with screws at haphazard (random) spacing (up to about 28 inches oc as shown in photos). It makes sense that this spacing would be controlled by loading but is there an industry standard for a minimum spacing for this connection?

Thank you.

 

[Jerehmy]

Hey Jim,

From AISI 2007 Section E4.2 - "The distance from the center of a fastener to the edge of any part shall not be less than 1.5d. If the end distance is parallel to the force on the fastener, the nominal shear strength[resistance] per screw, Pns, shall be limited by Section E4.3.2"

 

[dhengr]

Jim:
You should find some edge distance criteria in the AISI “Cold-Formed Steel Design Manual” and other such ref. materials. It would be a function of the screw or bolt dia., their allowable loads; and the thickness and mech. properties of the cold-formed material; and the direction of the loading. Some of the photos seem to how that the screws were loaded perpendicular to the edge, and the edge distance was very small, and you would expect tear out in this case. Looks just like you would expect to see it happen. While a larger edge dist. and loading along the length of the member would be no problem. I’d call this a dropped soffit. Other than DL what loads were on it. Were there any differential pressures from one side of the soffit to the other? You kinda have to look at these connections one at a time for cap’y, loads, details, edge dist., etc., until you get a feel for how they work. We just can’t write enough standards and codes to prevent or guard against builder incompetence, when they don’t read the stds. anyway. This appears to be fairly careless workmanship.

 

[TDIengineer]

What gauge is your top track? I often see suspended light gauge framing severely under-designed.

I like to check my top track in bending between fastener points as you have the track working in the weak axis, especially if fasteners are more than 32" o.c.

Where the vertical studs only at 24" o.c.? Normally shear isn't a failure mode, but tensile pull out, but this one is definitely a shear failure at the top track to stud connection. Once 1 screw failed, it zippered from load transfer to the adjacent screws, then the whole thing failed.

 

[TDIengineer]

Note:

If the drywall on at least one side was extended all the way to the top track, this wouldn't have failed...The additional drywall screws would have helped considerably for the vertical loads, and the gyp bd itself could have worked in tension for its selfweight. Always take care when you don't extend the gyp!.. also make sure you have bridging if you don't have gyp on both sides..

 

[jayrod12]

If you're in Canada the CSSBI cold formed steel book is the way to go for this. I don't have the book handy so I can't give you the exact name.

 

[wannabeSE]

Besides the AISI codes for structural cold formed steel, there is ASTM C 754, Standard Specification for Installation of Steel Framing Members to Receive Screw-Attached Gypsum Panel Products. I did not see any screw edge distance specifications in the standard. But, it does require the runners (tracks) of typical partitions to have anchors (nails, screws, pdfs etcetera) within 2" of each end and at 24"OC max. For soffits, I typically require the top track to be anchored at each stud.

 

[racookpe1978]

I have never before heard of drywall "needed" as a structural member to keep the rest of the structure from falling down .... 8<)

So, a more fundamental question: Why were the "too light, too little" sections approved in the first place?

 

[a2mfk]

What is the horizontal wood member in Photo 1, it looks like a ledger of some sort?

The top track is still attached after the failure, so I am not sure that this is the ultimate cause of the failure despite the fact there were edge distance failures.

I think Photo 9 and 10 shows that the horizontal wood blocking pulled out of the bottom chords of the trusses.

Photo 11 shows (I think) a pull-through failure of the top track fastener, which was used to fasten the track into the wood blocking.

This is if I am understanding your description and photographs correctly. It also appears the design (if any) had at least 3 possible failure modes.

The initial failure may have been top track edge failures that caused load redistribution to overload one of the horizontal wood blocking members, causing a pull-out failure from the bottom chord of the truss, then further load redistribution to the other horizontal wood blocking connections, and then we all know how that ended...