Turnbuckles and Clevises for Wind Bracing
Turnbuckles and Clevises for Wind Bracing
(OP)
The company I work for likes using round rods for bracing low rise industrial building structures.
Using A307 Rod, the turnbuckle becomes the weak link, per the Safe Working Loads provided in the AISC, 9th edition.
They site a 5:1 safety factor and claim it due to rigging and dynamic loading.
If you reduce it to 3:1 you get compatable allowable tensile loads to the rod itself.
I know this type of bracing is used in pre-engineered buildings all the time. What criteria do they follow?
Anybody reduce the 5:1 safety factor when turnbuckles are used in wind bracing?
Our construction guys think I'm nuts when I bump the rod sizes up over 1" diameter because of these 5:1 loads. And I can't say I blame them....it looks like "typical engineering over-kill".
Using A307 Rod, the turnbuckle becomes the weak link, per the Safe Working Loads provided in the AISC, 9th edition.
They site a 5:1 safety factor and claim it due to rigging and dynamic loading.
If you reduce it to 3:1 you get compatable allowable tensile loads to the rod itself.
I know this type of bracing is used in pre-engineered buildings all the time. What criteria do they follow?
Anybody reduce the 5:1 safety factor when turnbuckles are used in wind bracing?
Our construction guys think I'm nuts when I bump the rod sizes up over 1" diameter because of these 5:1 loads. And I can't say I blame them....it looks like "typical engineering over-kill".






RE: Turnbuckles and Clevises for Wind Bracing
RE: Turnbuckles and Clevises for Wind Bracing
Please remember to design your connections for stiffness as well as strength for rod bracing. I've seen many details where bracing was connected to the center of a column web with nothing bringing the load to the flanges. There have been a good many documented collapses because of this problem. Even if the web is strong enough, the web may not be stiff enough for proper bracing.
RE: Turnbuckles and Clevises for Wind Bracing
RE: Turnbuckles and Clevises for Wind Bracing
I agrree with your logic JAE, that is resonable and consistant with the design of the other building elements.
The 3:1 is what I'm gonna go with.
It is still conservative since overall lateral stiffness and stability has many other contibutors that are ignored for simplicity.
RE: Turnbuckles and Clevises for Wind Bracing
I have used up to about 1.5 inch rods on an industrial building .
The guys on site always complain that things are overdesigned but they have no point of reference.
The only thing to note is that the bigger the rod, the more it is going to pull things inward when it is tensioned up. Many of the typical connections dont work for large rods either.
RE: Turnbuckles and Clevises for Wind Bracing
Minimum destructive test force x 0.8(Capacity reduction factor)
From this I find that a quality grade P turnbuckle is acceptable for structural purposes for matching mild steel rod size.
When designing rods remember to design as a member not as a connector. i.e. use yield of the rod rather than tension capacity of the treaded part to calculate design strength.
RE: Turnbuckles and Clevises for Wind Bracing
Dik
RE: Turnbuckles and Clevises for Wind Bracing
Ref: A3 in the 2005 Specifications