spats
Structural
- Aug 2, 2002
- 655
I've come across a problem with what should be a standard handrail connection using aluminum. See attached sketch. The handrail is attached to the vertical guardrail posts with a bent rod bracket. It's common for steel stairs to use a 5/8" to 3/4" solid rod. Handrails, per the Code, have to be designed for 50 plf or 200 lb. concentrated load. The 200 lb. concentrated load is the problem. If the load is applied horizontally, it seems there will be a decent distribution of the load through the guardrail and handrail system, so that a single bracket will not experience the entire 200 lb. load. When the load is applied vertically, only the handrail can act to distribute the load, and it seems a single bracket will see most of the 200 lbs.
The rod bracket needs to be cold-bendable, so 6063-T5 aluminum is specified... Fu = 22 ksi, Fy = 16 ksi. A 3/4" diameter rod isn't even close to working, especially since the 2005 Specification for Aluminum Structures says Fu = 17 ksi and Fy = 8 ksi within 1" of a weld. I could possibly justify a 1" rod working, but it would essentially need to be full-pen welded to the post. The post itself could be the weak link in terms of tear-out of the face of the pipe. Also, a 1" rod is not practical for attaching 1 1/4" and 1 1/2" O.D. handrails... it's almost as big as the handrails and creates an issue of passing your hand over the bracket without having to let go of the rail.
I don't know how to make this work without inventing a whole new type of bracket. Do others have experience with this problem? Do you let the bracket connection yield, but not break? Maybe the Specification for Aluminum Structures does not actually apply to handrails (I don't think it does), but you can't ignore the reduced strength at an aluminum weld. Any insight would be greatly appreciated.
The rod bracket needs to be cold-bendable, so 6063-T5 aluminum is specified... Fu = 22 ksi, Fy = 16 ksi. A 3/4" diameter rod isn't even close to working, especially since the 2005 Specification for Aluminum Structures says Fu = 17 ksi and Fy = 8 ksi within 1" of a weld. I could possibly justify a 1" rod working, but it would essentially need to be full-pen welded to the post. The post itself could be the weak link in terms of tear-out of the face of the pipe. Also, a 1" rod is not practical for attaching 1 1/4" and 1 1/2" O.D. handrails... it's almost as big as the handrails and creates an issue of passing your hand over the bracket without having to let go of the rail.
I don't know how to make this work without inventing a whole new type of bracket. Do others have experience with this problem? Do you let the bracket connection yield, but not break? Maybe the Specification for Aluminum Structures does not actually apply to handrails (I don't think it does), but you can't ignore the reduced strength at an aluminum weld. Any insight would be greatly appreciated.