yudkib
Structural
- Apr 29, 2012
- 7
Hi all, strange thing I think I have figured out but am trying to decide conclusively.
I'm working with a client who is replacing their above-grade deck. The decking will be 5/4x6 STK western red cedar with a 16" spacing of PT Pine joists. They also want to do a custom handrail / guard detail in the same material. OK. From the way things seem, I suspect the town will want some backup on the detailing.
So the question I have is: what's the allowable bending stress for 5/4 x 6 STK western red cedar?
I'm not sure the guidance exists. Some observations:
- STK is an architectural designation, it is not a structural designation. When I talk to the distributors they basically say "ask WRCLA."
- WRCLA has a guide, and they say for 5/4x6 STK use a 16" spacing of joists. No engineering data for boards. OK.
- NDS only publishes for 2" nominal and thicker in the supplement (700-725psi for #2/#1). WRCLA just references the same NDS values.
- NDS does have an area for decking, but again, it's 2" and thicker. It seems to more or less be the product of Fb, the size factor, and the flat use factor - coming out to 1050psi. There is still no clarification on whether this applies to STK, just "commercial grade" decking.
- The grading guides have at least some information on what passes as "commercial grade" - and the STK probably would.
- Back to NDS - the only thing I've seen referencing the allowable stress of boards was at the end of table 4A, which basically said "you can probably use these stresses for boards." But there is no note in the decking table.
- By most indications (looking at pictures on the internet), STK seems to be mixed #1/#2 grade.
So my plan is use the 700psi for #2 cedar lumber 2"-4" thick with the flat use and size factors and see where I end up.
But now out of curiosity - does anyone know who governs the allowable stress of boards under 2" thick?
I'm working with a client who is replacing their above-grade deck. The decking will be 5/4x6 STK western red cedar with a 16" spacing of PT Pine joists. They also want to do a custom handrail / guard detail in the same material. OK. From the way things seem, I suspect the town will want some backup on the detailing.
So the question I have is: what's the allowable bending stress for 5/4 x 6 STK western red cedar?
I'm not sure the guidance exists. Some observations:
- STK is an architectural designation, it is not a structural designation. When I talk to the distributors they basically say "ask WRCLA."
- WRCLA has a guide, and they say for 5/4x6 STK use a 16" spacing of joists. No engineering data for boards. OK.
- NDS only publishes for 2" nominal and thicker in the supplement (700-725psi for #2/#1). WRCLA just references the same NDS values.
- NDS does have an area for decking, but again, it's 2" and thicker. It seems to more or less be the product of Fb, the size factor, and the flat use factor - coming out to 1050psi. There is still no clarification on whether this applies to STK, just "commercial grade" decking.
- The grading guides have at least some information on what passes as "commercial grade" - and the STK probably would.
- Back to NDS - the only thing I've seen referencing the allowable stress of boards was at the end of table 4A, which basically said "you can probably use these stresses for boards." But there is no note in the decking table.
- By most indications (looking at pictures on the internet), STK seems to be mixed #1/#2 grade.
So my plan is use the 700psi for #2 cedar lumber 2"-4" thick with the flat use and size factors and see where I end up.
But now out of curiosity - does anyone know who governs the allowable stress of boards under 2" thick?
