hole locations wood joists

[AJG]

Some building codes show locations for holes in wood
floor joists at different locations. One code showed holes only to be located within middle third of span, others showed only within outer thirds of span and some do not even show locations. Both 2" clear from top and bottom and D/3 for dia. WHICH WOULD BE THE BEST LOCATION
WITHIN ENGINEERING STANDARDS.

 

[curvbridger]

The hole should be sized and placed depending on the controlling capacity of the wood member. It is assumed that the member capacity is controlled by shear in the end thirds and controlled by bending in the middle third. The joist will tolerate more shear if the hole is a notch at top or bottom, and will tolerate more bending stress if the hole is near the center.

 

[PvB]

From a structural stand point, it depends what stresses are critical for your case. Wood is particularly weak in horz. shear, which for a uniform load will be max near the ends (d dist from support). Longer spans will be critical for flexure, generally toward the center. Wood is also weaker in tendion than compression so cutouts in the tension zone are a bit worse. But the thing really to watch is splitting or cutting notches that may produce spliting along the grain. The National Desing Spec. (NDS 2001) gives guidelines of how to avoid putting notches in the wrong places (NDS 4.4.3)

Peter von Buelow
Univ. of Mich. - TCAUP