wood I joist

[inspectorjeff]

what is the rationale for allowing 98% of the osb web to be cut out of wood I joist? they recommend cutting holes in the center of the span. How does this affect the resistance to maximum bending moment at the center? Would the unit act like a truss with 45 degree force lines thus aviding the hole? Inspector Jeff in Florida

 

[whyun]

near the mid span of the TJI, where bending is maximum, most of the tension is on the bottom chord and most of the compression would be in the top chord. OSB web will experience a small amount of tension and compression via resin between the flange and web but can be neglected. Thus, having a hole in the center of the web is not a big concern.

OSB web on the other hand carries most of the shear so TJI catalog tabulates some distance from the support where holes are not allowed.

I am not sure about the 98% value.

 

[Ron]

Jeff...OSB web only contributes about 25 percent of bending resistance and about 70 percent of shear resistance. As whyun said, not a big deal about cutting through center of web in the middle 1/2 of the joist, where bending occurs, but wouldn't want to do that in the 1/4 near each end.

I think the code maximum is 60 percent cut out, though you should verify that with our "fabulous" FBC 2001!!

 

[anthonyc007]

I have tested I-joists in full scale bending tests. The emirical results suggest that cutting large holes in the center is acceptable. However, it is interesting to note, that I-joist performance drops significantly with small notches in the flanges. Watch out for careless plumbers and electricians!