Calculating the capacity of a floor joist that has been bored

[Qwikduster]

I have performed numerous methods to determine the amount of load carrying capacity that is lost when you bore through a floor joist--or in this situation several bores along the center of the floor joists in a new home. My calculations show a very minimal loss in capacity, and is really negligible--however,I would like to know if I missed soemthing, so I need to know what is the best method to follow in computing this loss??

This is a case of an electrical contrator boring up to in some cases 10- 5/8" diameter holes along the center of 20-2x10 floor joists spanning 13'-6". The holes are concentrated in the first 18" from the bearing wall. To apease the building contractor and local inspection officials, I specified placing a 2x6 wall adjacent to the masonry exterior wall (homeowner is finishing the basment later)and used a 2x6 brace extending 18" out from the wall(acting as a tray) attached to each joist directly under the furthest holes to provide any necessary support--however I would like to know how much capacity was actually lost in this case??
Any help is greatly apprecaited!!
Thanks!!

 

[CJJS]

I would calculate a new moment of inertia, based on the cross section with the hole. Then, check the shear stress and bending stress at that location. Bending stress is likely not to be an issue, since you indicate is is located near the support. The shear stress is VQ/Ib. Q being the first moment about the location of concern (i.e. the top/bottom of the hole). I is the new moment of inertia based on the cross section with the hole. b is the width of the 2x member (or 1.5 for a 2x10) and V is obviously the shear force in the beam at the location of the hole.
Compare your calculated value of shear stress to the tabluated allowable value (times any applicable factors) in the NDS.

 

[SlideRuleEra]

Take a look "Material & Methods" on page 2 (of 7 pages) and Table 1, "Limiting Characteristics for Nominal 2 x 10 dimensional lumber..." on page 3. This Forest Products Journal article is titled "Evaluation of Lumber Recycled From and Industrial Military Building". Here is the link

http://www.fpl.fs.fed.us/documnts/pdf1999/falk99a.pdf

http://www.SlideRuleEra.net

 

[SlideRuleEra]

Also see the statement (on page 1 of 6) about how little information is available on this subject in "Effect of Drilled Holes on the Bending Strength of Large Dimension Douglas Fir Lumber"

http://www.fpl.fs.fed.us/documnts/pdf2003/falk03a.pdf

http://www.SlideRuleEra.net

 

[Qwikduster]

Thanks for the quick and excellent replies!!!!
CJSchwartz--absolutely!! You confirmed my approach, and indeed the shear was my concern--hence the reason for the 2x6 wall under the affected area (of course it is overkill).

SlideRuleEra- Thankyou for the articles--I have printed them out and I am keeping them on file for future reference. I too have discovered the apparent limited amount of information on a subject I see almost daily. It seems I'm getting a lot more calls for help on this question recently...."Following the code" isn't enough to keep contractors from drilling holes where they need to go....for me to know what the actual lossses are, or the best way to calculate the loss when contractors have to bore in an area that is borderline, or not allowed in the codes is absolutely necessary.

If anyone else has a different approach--PLEASE share it!!!
Thanks again for all the responses!!!

 

[RARWOOD]

Use floor trusses.