JOIST UPLIFT BRIDGING LOAD TEST
JOIST UPLIFT BRIDGING LOAD TEST
(OP)
We have a roof where we are removing a ballasted roof and replacing it with a single ply membrane roof. We now have a small net uplift on the roof.
The SJI Specifications say that bottom chord bridging is required near the first B/C panel point.
We have done some limited testing on a mock-up and have determined that the tested joists have a moderate uplift capacity without this additional bridging.
What I am wondering is have there been any studies that establish general guidelines for this situation. There are several different joist sizes on this project and it is beyond our budget to do multiple load test to prove every joist type works.-
The SJI Specifications say that bottom chord bridging is required near the first B/C panel point.
We have done some limited testing on a mock-up and have determined that the tested joists have a moderate uplift capacity without this additional bridging.
What I am wondering is have there been any studies that establish general guidelines for this situation. There are several different joist sizes on this project and it is beyond our budget to do multiple load test to prove every joist type works.-






RE: JOIST UPLIFT BRIDGING LOAD TEST
RE: JOIST UPLIFT BRIDGING LOAD TEST
RE: JOIST UPLIFT BRIDGING LOAD TEST
h
Or you could measure the bottom chords, figure out the section properties and provide bridging (bracing) to keep the kl/r under 150 or so. I'm sure the uplift compression on the bottom chord is small, but you still need some bracing.
Third option is to call someone besides Vulcraft. Quincy Joist or the SJI comes to mind.
RE: JOIST UPLIFT BRIDGING LOAD TEST
RE: JOIST UPLIFT BRIDGING LOAD TEST
Do you have a reference for the 1.7L. I agree with your logic but i would feel more comfortable seeing it in print.
RE: JOIST UPLIFT BRIDGING LOAD TEST
RE: JOIST UPLIFT BRIDGING LOAD TEST
"Before uplift bridging was required the industry used a k-factor of 2 for checking buckling of the bottom chord and 1st web member." This is stated in older versions of Technical
Digest #6.
The B/C bridging requirement was added in late 1985 when the K series joists were introduced.