Joist bottom chord out of plane bowing
Joist bottom chord out of plane bowing
(OP)
Hi all,
I received an email today from a jobsite asking what the tolerances are for a joist bottom chord to be bowed 1" to 2" out of plane compared to the top chord. The bridging has already been installed.
Has anyone else ever run into this? I would assume a joist is not designed to perform while bowed as described? Would you recommend diagonal cross bracing at the center?
FYI, we are design-build and this project was actually designed by another firm. Of course I want to tell the PM to ask the engineer of record, but they like to have an opinion from us, the in-house engineers, before going to the next level.
Thanks! -K
I received an email today from a jobsite asking what the tolerances are for a joist bottom chord to be bowed 1" to 2" out of plane compared to the top chord. The bridging has already been installed.
Has anyone else ever run into this? I would assume a joist is not designed to perform while bowed as described? Would you recommend diagonal cross bracing at the center?
FYI, we are design-build and this project was actually designed by another firm. Of course I want to tell the PM to ask the engineer of record, but they like to have an opinion from us, the in-house engineers, before going to the next level.
Thanks! -K






RE: Joist bottom chord out of plane bowing
RE: Joist bottom chord out of plane bowing
I only suggest this because regardless of the opinion of other engineers (for example, I'd thikg the bowing could be problematic if the joists are exposed to uplift pressures and the bottom chord goes into compression), these people do joists day in and day out and may have some practical advice.
RE: Joist bottom chord out of plane bowing
Every time I find something wrong with a joist onsite I refer the problem back to the manufacturer. If there is a problem they will typically suggest some sort of repair. If some sort of repair is required is should be approved by the EOR.
RE: Joist bottom chord out of plane bowing
RE: Joist bottom chord out of plane bowing
Thank you for your responses. As a follow up, we contacted SJI and their response was
"There are no set standards except that the erector is to utilize the bridging to assure that the joists are reasonably true and plumb."
So, who is to determine what is reasonably true and plumb? I guess the EOR, too bad there are no standards to refer to!! Especially if something were to go wrong. We will have the PM contact the joist mfg.
I have also attached a photo of the condition.
RE: Joist bottom chord out of plane bowing
RE: Joist bottom chord out of plane bowing
RE: Joist bottom chord out of plane bowing
Why don't you send the issue to the joist supplier for this job? They designed it and know how close it would be to capacity under the design loads. As a gut feeling, I would expect adding a couple of additional rows of diag. bridging would bring it back to design capacity. But just check with the joist supplier.
RE: Joist bottom chord out of plane bowing
For the wood truss industry, the Truss Plate Institute specifies 2% as maximum vertical lean and L/200 for bow (as in the photo) where L = length of truss in inches.
Er, wouldn't L/200 = 0.5%???
The old source doc was HIB-91, but I can't recall new name/number of the doc that replaced it.
J.
A John Gironda III, P.E.
"As long as you are in the seat...make a difference"---Capt James T. Kirk
RE: Joist bottom chord out of plane bowing