Robcat71
Structural
- Sep 9, 2020
- 16
Hi All,
I have a scenario where a contractor is proposing to utilize tie-off anchors that attached directly to the metal roof deck using several self tapping screws (approx. 25 locations). Per OSHA, the tie off design load is 5,000 lbs. and shall have a factor of safety of 2. My concerns are with the attachment of the deck itself to the roof structure, and the deck capacity. If I am understanding correctly, the base reaction of the tie off anchor will put the decking in combined bending and compression. Would the deck also have to resist the vertical shear/tension along the edge of a support that results from the base moment couple? I am not sure how you could rely on the deck in the weak direction (assuming it meets the shear, compression and flexural demand) with just a couple of side lap fasteners to transfer the load between panels. Does anyone have a good reference for the deck design under this type of loading?
Has anyone successfully designed this type of tie off anchor? I am not sure why such a product exists if its not feasible in most applications. I am working with 20 GA type B metal roof deck, fastened on a 36/4 pattern with PAF's.
The other option is to attached the tie-off directly to the roof steel, but results in torsion that the framing and connections were not designed for. The contractor is obviously trying to install these anchors without adding additional framing to brace the roof beams, but that is how I have typically designed and detailed roof tie offs in the past.
I appreciate all and any input / references.
Thanks!
I have a scenario where a contractor is proposing to utilize tie-off anchors that attached directly to the metal roof deck using several self tapping screws (approx. 25 locations). Per OSHA, the tie off design load is 5,000 lbs. and shall have a factor of safety of 2. My concerns are with the attachment of the deck itself to the roof structure, and the deck capacity. If I am understanding correctly, the base reaction of the tie off anchor will put the decking in combined bending and compression. Would the deck also have to resist the vertical shear/tension along the edge of a support that results from the base moment couple? I am not sure how you could rely on the deck in the weak direction (assuming it meets the shear, compression and flexural demand) with just a couple of side lap fasteners to transfer the load between panels. Does anyone have a good reference for the deck design under this type of loading?
Has anyone successfully designed this type of tie off anchor? I am not sure why such a product exists if its not feasible in most applications. I am working with 20 GA type B metal roof deck, fastened on a 36/4 pattern with PAF's.
The other option is to attached the tie-off directly to the roof steel, but results in torsion that the framing and connections were not designed for. The contractor is obviously trying to install these anchors without adding additional framing to brace the roof beams, but that is how I have typically designed and detailed roof tie offs in the past.
I appreciate all and any input / references.
Thanks!
