3/4" holes in Floor Joists 2

[Jim5000]

Hello, my floor joists have one 3/4" holes in 10 of the floor joists (in a row, with PEX tubing in them). The problem is that they are located only 1" from the bottom of the joists! the Joists are 2x8 wood on 16" cetres. They span 12 feet.

Do I have a structural issue? If so, how do I repair the problem?

thanks in advance for your advice/discussion!

 

[woodman88]

shobroco - In the US and Canada the building codes are the people, by way of their elected officials, way of setting the standard of safety that they are willing to accept for structures to be built and maintained by. As engineers we are obligated to follow these standards, whether we agree with them or not. If you feel your argument to be valid then you should present it to the code officials to change the code.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[shobroco]

I have presented it as a proposed change, more than once. The last time, I was told that the introduction of performace standards in addition to prescriptive standards would deal with it, however it depends how you read them. The real problem is that codes are always written broad brush, to cover the worst case, and usually do not permit qualified individuals to use professional judgement. An exemption in our code actually demonstrates the validity of my argument: conversion of an existing building into a restaurant is permitted to use a live load of 2.4 kPa (50psf) if the building is under X sq.m. (I forget the exact number) Obviously if you have such an exemption, you have to have a cut-off point, but what possible scenario would double the floor loading in a building 1 sq.m. larger than another of exactly the same use?

 

[Ron]

Of course the straps will work and they will work long before failure occurs. The design accommodates 40psf....which is not there yet. So unless you load those joists to 40 psf +DL and then put the straps in place, you won't have to wait for failure for them to work!

Put the straps in place like Mike McCann says...then have your orgy.

 

[woodman88]

Ron - For the straps to work. The nails have to achieve the required critical slip on each side of the hole. Are you saying that the bottom edge of the joist will elongate enough to meet the critical slip of the nails before failure?

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[woodman88]

Look at it this way. Given the number of times that plumbers and electricians have drilled holes in the bottom of joists. If the metal strap worked then there should be tons of information about it on the Internet and structural magazines. If you can find any information please share it with us.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[EngineeringAdam]

Actually, I would think that there is no literature on straps being used on the bottom of joists because no one cares about joists. It's pretty common to have holes drilled through them without any consideration from plumbers, etc. and without the engineers ever seeing the modifications. And I haven't read anything on joist failures due to holes because of plumbers.

I think Ron might have a point about the extra 40psf live actually getting the strap to engage though. I think a quick check would be able to see the validity of that assumption.

See what the 40psf live load will cause in deflection, if the joists are long enough the elongation along the bottom of the joist might be enough to engage the nails and strap.

Although, off the to top of my head I am not sure what a 10d nail will slip in a condition like this... So maybe this check would prove the strap useless.

 

[MiketheEngineer]

I do CARE about joists - have had too many massacred too many times by electricians and more massacred by plumbers with their 2'' pipes!!

Had a million dollar plus home with rich Italian marble on the floor that was highly mis-treated by an electrician. I read him the the riot act and made them fix the joists. NOBODY is going to crack my marble!! And it hasn't in 15 years!!

 

[Ron]

woodman88...while I agree with your excellent advice most of the time, in this case I'll have to disagree. Repair and strengthening straps can be used in tension applications such as this or on the sides of top or bottom plates.

Most nailings of straps that I've seen don't hit the center of the hole. Further, the holes are sized to use either 10d or 16d nails. If 16d nails are used, there's little slip required to mobilize the shear in the nails and then the tension in the strap.

Strains between steel and wood are so incompatible that I feel mobilization would occur long before it could be predicted by analysis.

 

[woodman88]

Ron - If you have $15 you can get a pdf of the NTIS report ADA013987 "Evaluation of Expedient Techniques for Strengthening Floor Joist Systems in Residential Dwellings." In the attached link it gives some information about the results. It is from 1975 but I do not think that the lumber, straps and nails have changed enough to invalidate the results.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[Ron]

Garth...I tried. Not available. Synopsis I found seems to support the use of straps, although they were the full length of the span.

 

[Ron]

I'll try another route to get that paper. I agree it might be useful, even if a bit older.

 

[woodman88]

Ron - Have you tried this link?

http://www.ntis.gov/

If you type in "ADA013987" it comes up.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.