Knots In Joists (engineers) - Building & Construction - Page 2 - DIY Chatroom Home Improvement Forum
Advertisement


Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Building & Construction

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread
Display Modes
Old 10-30-2010, 08:18 PM   #16
Member
 
Join Date: Dec 2008
Location: Fairbanks, AK
Posts: 1,941
Rewards Points: 1,188
Default


Quote:
Originally Posted by Daniel Holzman View Post
How a bolt increases the section modulus of a wooden beam.
Dan: Thanks. I knew about the plate, but did not see what the bolt itself might be able to do. j
jklingel is offline   Reply With Quote
Sponsored Links
Advertisement
 
Old 10-30-2010, 09:12 PM   #17
Member
 
Join Date: Oct 2010
Posts: 33
Rewards Points: 25
Default


Dan, is it true that span tables an such are designed with the idea that errors will be made so it would be ok to live with what I have
artmark is offline   Reply With Quote
Sponsored Links
Advertisement
 
Old 10-30-2010, 09:26 PM   #18
Member
 
Join Date: Dec 2008
Location: Fairbanks, AK
Posts: 1,941
Rewards Points: 1,188
Default


Art: I doubt that any engineer is going to give advice like that over the Net. Way too much liability. So, don't feel bad if Dan does not get back on it. I feel that it is a foregone conclusion that ANY tables like that have a built in fudge-factor because the world is not a perfect place; not the wood, not the installer. Hasn't your place been working for a while as is? I forget what you said earlier. j
jklingel is offline   Reply With Quote
Sponsored Links
Advertisement
 
Old 10-30-2010, 10:44 PM   #19
Registered User
 
Join Date: Mar 2009
Posts: 11,730
Rewards Points: 526
Default


Compare your holes to minimum code: http://www.mybuildingpermit.com/Cons...Sheet06_11.pdf
http://arch.umd.edu/Tech/Structural_..._Guide_A11.pdf

Technical: holes and location: http://docs.google.com/viewer?a=v&q=...R84KitBdBk9OIA

Gary (the cat that found "strengthen bouncy floors"). lol
__________________
If any ads are present below my answer or words underlined/colored, I do not condone/support/use the product or services listed/linked to, they are there without my consent.
17,000 dryer fires a year, when did you last clean the inside of the dryer near motor or the exhaust ducting?
Gary in WA is offline   Reply With Quote
Old 10-31-2010, 10:06 AM   #20
Member
 
Join Date: Oct 2010
Posts: 33
Rewards Points: 25
Default


compared to minimum code the 3 holes are 1/2 to 1/4 of a inch to close to the edge the were drilled about 3 years ago to run wiring for satellite tv was thinking of sistering with plywood or similiar joist if I sister with plywood I can sister the entire lengh If I use anothe joist I can also sister from bearing to bearing and not the cantilivered portion the holes are in the bearing portion
artmark is offline   Reply With Quote
Old 10-31-2010, 12:32 PM   #21
Civil Engineer
 
Join Date: Mar 2009
Location: Boston
Posts: 5,832
Rewards Points: 5,246
Default


All tables in code books incorporate a safety factor. Exactly how the safety factors are incorporated is very complicated. There are typically three or more safety factors built into span tables. The first factor is a "workmanship" factor, which is supposed to account for improper installation technique (i.e. bolts are not properly tightened, dimensions are slightly off). The second factor is a "material factor", which is designed to account for materials whose actual breaking strength is less than design strength (i.e. 3000 psi design concrete is only 2800 psi). There is also a "load factor", meaning that the design load may be 40 percent or greater than the actual maximum anticipated load, for example on a deck my town uses 50 psf loading, whereas realistically it would be very hard to load a deck to 50 psf. Some codes incorporate the "load factor" as a maximum stress factor, for example wood which is expected to have a modulus of rupture (maximum bending stress) of 2000 psi may be assigned a maximum allowable stress of say 1200 psi in the code book, which effectively incorporates a safety factor of almost 70 percent.

The complex thing is that different codes use very different approaches, so in some cases the material factor, workmanship factor and load factor are all combined together, in other cases they are computed separately and combined in complicated ways, and some codes are based on load factor ("load factor design"), while other codes use allowable stress or working stress safety factors.

So to try and answer your question, yes the code for your building incorporated a safety factor, without detailed research you don't know what that safety factor is, and in any case the important question is whether the out of code work compromises safety, which is a question no one can answer without a hands on inspection of the site and some serious analysis.
Daniel Holzman is offline   Reply With Quote
Old 10-31-2010, 03:57 PM   #22
Member
 
Join Date: Oct 2010
Posts: 33
Rewards Points: 25
Default


so from what you are saying a engineer needs to re engineer the work with it's faults and determine wether it is safe?
artmark is offline   Reply With Quote
Old 10-31-2010, 06:25 PM   #23
Civil Engineer
 
Join Date: Mar 2009
Location: Boston
Posts: 5,832
Rewards Points: 5,246
Default


This thread started out as an inquiry about the difference between knots, bolts and holes. Then it morphed into a question about the adequacy of a structural member with a cantilever and some holes in improper locations. If there is no problem with the house, I guess I am confused about why you want to reengineer anything. If the house isn't falling down, there are no cracks, you don't see any evidence of failure, perhaps it is OK the way it is. If you really want to know, you can certainly hire an engineer.
Daniel Holzman is offline   Reply With Quote
Old 10-31-2010, 07:11 PM   #24
Member
 
Join Date: Oct 2010
Posts: 33
Rewards Points: 25
Default


shows no signs of falling down but I am concerned it is a matter of time that there could be a failure and a failure would be more expensive to repair as per the knots my thoughts were if there is a 1" not on the tension side that the joist has already been reduced hence if a hole protrudes into the minimum code area of 2" from edge that it would be a similiar deffect as the knot and the joist would be just as effective just one is a violation the idea of engineering is to confirm it
artmark is offline   Reply With Quote
Sponsored Links
Advertisement
 
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Double floor joists harsuwind Building & Construction 3 09-15-2010 07:35 AM
Supporting joist under cracked tile JT31 Building & Construction 2 08-26-2010 08:00 AM
Floor Joists of different sizes HooKooDooKu Drywall & Plaster 7 02-04-2010 05:43 PM
Sister or Replace Floor Joists brando1118 Carpentry 25 10-26-2008 08:43 PM
help with 2nd floor joists g heil Building & Construction 5 09-12-2008 06:41 PM




Top of Page | View New Posts