The Forestry Forum is sponsored in part by:

iDRY Vacuum Kilns


Forestry Forum
Sponsored by:


TimberKing Sawmills



Toll Free 1-800-582-0470

LogRite Tools



Norwood Industries Inc.




Your source for Portable Sawmills, Edgers, Resaws, Sharpeners, Setters, Bandsaw Blades and Sawmill Parts

EZ Boardwalk Sawmills. More Saw For Less Money!

STIHLDealers.com sponsored by Northeast STIHL


Woodland Sawmills

Peterson Swingmills

 KASCO SharpTech WoodMaxx Blades

Turbosawmill

Sawmill Exchange

Michigan Firewood, your BRUTE FORCE Authorized Dealer

Baker Products

ECHO-Bearcat

iDRY Wood Lumber Vacuum Drying for everyon

Nyle Kiln Dry Systems

Chainsawr, The Worlds Largest Inventory of Chainsaw Parts

Smith Sawmill Service



Author Topic: Re: General Rules for Joinery Design  (Read 992 times)

0 Members and 1 Guest are viewing this topic.

Offline Rgdsolution

  • member
  • *
  • Posts: 3
  • Location: Western massachussets
  • Gender: Male
  • I'm new!
    • Share Post
Re: General Rules for Joinery Design
« on: May 19, 2021, 10:39:06 PM »
Iíve got two questions about rules of joinery. Iím building a 16x20 timber frame with basement. I have a girder spanning the 15í with a post under it, the beam is rated for 6300ibs on each side and I need 2600ibs but for sake of argument for more than one reason letís say itís rated for 2900ibs. On each side and Iím only over the margin by 300ibs. ( I found an imperfection in the way of a large rotted knot but found good wood above it) Now the main reason I chose this method was because the beam wasnít supposed to be spanning a basement but regardless instead of tenons in the center of the beam I chose to cut notches 1 3/4 deep and 4Ē tall for the floor joists, now mind you most of it is in the half round sides - I only milled two side but for sake of argument I want to pretend itís a square beam rated this way. My question isnít really only for this application but in general if all of my joints were very tight and I squeezed wood glue into any openings I could find would that recreate the same compression strength on the top of the beam and eliminate my worries? Is their any way to calculate a strength loss for instance or would it be close enough to call fine?? My other question is whether anyone has experience using steel plate of some sort to support a weak area where a knot was found maybe passing the knot on each side by a foot or so with three bolts going all the way through? 

Offline Rgdsolution

  • member
  • *
  • Posts: 3
  • Location: Western massachussets
  • Gender: Male
  • I'm new!
    • Share Post
Re: Re: General Rules for Joinery Design
« Reply #1 on: May 19, 2021, 11:03:21 PM »
Iíll add as well that the girder is 8Ē thick and Iím calling it 9Ē wide but the half rounds add at least an inch on each side? Any thoughts would help or especially verification that I canít fix my top compression strength - I wonder if theirs such a thing as hydraulic glue lol

Offline Jim_Rogers

  • Board Moderator
  • *****
  • Posts: 7744
  • Age: 69
  • Location: Georgetown, MA
  • Gender: Male
  • Keep your chisels sharp.
    • Share Post
    • jrsawmill.com
Re: General Rules for Joinery Design
« Reply #2 on: May 20, 2021, 06:56:56 AM »
I felt this topic needs to have its own thread, so I split it out.
Hopefully DonP will give you some advice on this subject.

Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Offline Don P

  • Senior Member x2
  • *****
  • Posts: 8543
  • Location: Southwestern VA
  • Gender: Male
    • Share Post
    • Calculator Index
Re: General Rules for Joinery Design
« Reply #3 on: May 20, 2021, 08:05:04 AM »
Hi Rgdsolution, welcome to the forum. I'm just an old carpenter so take it for what its worth.

I'm not going to pretend I have a full understanding of the problem but it sounds like your gut is telling you things about that timber.

A couple of thoughts from what the smart people say. When you notch into a beam for drop in joists or purlins the rectangular section remaining between the notches on each side is the beam thickness and then the full depth. So for argument if you take an 8"x 12" beam and notch in 3" from each face the beam becomes a 2x12... the penalty for breaking that top compression edge is severe!

Filling it in is a common thought, banish that thought. The joist will shrink in thickness, you are compressing side grain and the continuous fiber has been interrupted. You have destroyed a portion of that compression chord, no amount of bubble gum is gonna fix it.

If you use a tusk tenon or some form of mortise in the center, neutral axis, thereby not breaking the strap of wood on the top and bottom of the beam there is no penalty. Think about an I beam or a trussed type of joist, the top and bottom chords are doing the tension and compression work and the web is simply holding them apart and resisting the horizontal shear.

Unless the steel plate extends the full length as in a properly sized steel flitch plate I seriously doubt that is going to do it.

In other words, I'm listening to your gut and agreeing with it. I think we need to back up and rethink your design.

@Jim_Rogers, I was just looking at everyone's locations, you're still showing you're in Georgetown  ;)
The future is a foreign country, they will do things differently there - Simon Winchester

Offline Den-Den

  • Senior Member
  • ****
  • Posts: 569
  • Age: 64
  • Location: Lufkin Texas
  • Gender: Male
  • I'm new!
    • Share Post
    • Dennis Wood Art
Re: General Rules for Joinery Design
« Reply #4 on: May 20, 2021, 05:54:56 PM »
As Don said, there are issues here.
*  Beam that would have been rated for 6300 lbs on each side of a center support but has a large knot.  A knot that penetrates the sides and is positioned near the center vertically would have a minimal effect on bending resistance.  A large knot positioned near the top or bottom of the beam would have a devastating effect on bending resistance.
*  Mortises in the beam for joists  If they are only in the rounded sides and do not penetrate into the rectangle section that you used for coming up with the 6300 lb rating - no problem, otherwise you must re-calculate using the remaining width that is not compromised by the mortises.
You may think that you can or may think you can't; either way, you are right.

Offline Rgdsolution

  • member
  • *
  • Posts: 3
  • Location: Western massachussets
  • Gender: Male
  • I'm new!
    • Share Post
Re: General Rules for Joinery Design
« Reply #5 on: May 20, 2021, 11:23:27 PM »
Thanks for the input I had a feeling that was my problem I had originally planned on using a different beam and since I only milled the two sides of both of these beams I figured cutting out sections of the half round wouldnít affect it greatly but this beam is less of a quality piece and a bit smaller Iím going to recalculate itís worst case strength and redecide. I well you live and learn 

Offline bannerd

  • Full Member
  • **
  • Posts: 84
  • Location: Malone, NY
  • Gender: Male
  • Madman
    • Share Post
Re: General Rules for Joinery Design
« Reply #6 on: June 04, 2021, 01:46:13 PM »
Knots can change the direction of the wood grain too, so even if you have a knot in a generally location, there is also a deflection of grain somewhere around that knot.

Knots are not a bad thing at all and typically the very last thing to rot.  If a knot is in a good location where downward pressure would utilize the knot then that could be perfect.

If the knot is in a bad location where it could cause the grain to split or shear... I don't know if I would use it.  OR if the knot is in a location where it could fall out, again.. not sure I would use the timber.  I think at this point I would look at options of running a scarf joint or replacing the entire beam.

Offline Don P

  • Senior Member x2
  • *****
  • Posts: 8543
  • Location: Southwestern VA
  • Gender: Male
    • Share Post
    • Calculator Index
Re: General Rules for Joinery Design
« Reply #7 on: June 04, 2021, 08:01:03 PM »
I'd like to see the analysis of the scarf... and for a floor girder, certainly not.

Grading rules do address knot location. Ideally a knot would be along the neutral axis of the beam, second choice would be on the compression side. The problem there though is with the grain deviation the timber shrinks lengthwise around a knot, if you are crowning timbers the knot wants to be on the tension side, which is the last choice structurally. Nature ganging up on us.



The future is a foreign country, they will do things differently there - Simon Winchester

Offline bannerd

  • Full Member
  • **
  • Posts: 84
  • Location: Malone, NY
  • Gender: Male
  • Madman
    • Share Post
Re: General Rules for Joinery Design
« Reply #8 on: June 07, 2021, 12:19:53 PM »
I'd like to see the analysis of the scarf... and for a floor girder, certainly not.
We use scarf joints all the time for floor girders.  Depends where the stationary is, if there is a girder 20ft long and the scarf is in the middle then there is a problem.  Shearing or total failure will eventually occur before or after there is a massive dip in the flooring.  Columns can be place in the proper locations to remediate this.
Not sure of the total picture from the OP but there are lots of options.


Share via delicious Share via digg Share via facebook Share via linkedin Share via pinterest Share via reddit Share via stumble Share via tumblr Share via twitter

xx
General Rules for Joinery Design

Started by Jim_Rogers on Timber Framing/Log construction

40 Replies
74167 Views
Last post July 07, 2020, 01:35:59 PM
by Jim_Rogers
xx
Joinery Design and Designer Problems

Started by kettleviewtimber on Timber Framing/Log construction

11 Replies
5172 Views
Last post August 17, 2007, 10:16:36 AM
by Jim_Rogers
xx
Frame design and joinery check

Started by Phil H. on Timber Framing/Log construction

0 Replies
877 Views
Last post March 25, 2017, 01:13:31 AM
by Phil H.
clip
Design critique needed EDIT: added pic of design in post

Started by RPowers on Timber Framing/Log construction

11 Replies
1618 Views
Last post January 16, 2014, 04:02:32 PM
by D L Bahler
 


Powered by EzPortal