Wood Reinforcement 2

[jrengineer]

Can you reinforce an existing wood member with too much deflection with a steel WT memeber?
If so... would the WT need to be mechanically connected to the wood member, or may it be glued?

 

[SlideRuleEra]

Attaching a WT member would be tricky. A more straightforward solution may be to jack the wood member, to minimize it's deflection. Then add a pair of (through-bolted) steel plates, one to each each side - sort of a reverse flitch beam (two steel plates enclosing a wood member, instead of two wood members enclosing a steel plate).

I would use a pair of steel plates (instead of just one) to make sure the new composite remains symmetric about the y-axis.

http://www.SlideRuleEra.net

 

[UcfSE]

I have used an angle on each side of the wood beam in the past. The steel plates that SlideRule mentions would be easier IMO. The idea is to keep what you're doing symmetric about the axis of the cross section.

 

[MikeHalloran]

I spent a lot of time in engineering classes looking up at a large pyramidal wooden truss that was at the time sixty- ish years old, like I am now.

Two things stand out in my memory:

- The timbers were knot-free and unsplit anywhere.

- The metal fittings used a large number of smallish bolts, arrayed in neat patterns like aircraft rivets.

I've had occasion since to stand under a number of more modern timber trusses. Three things stand out in my memory:

- The timbers were split, multiply, in some cases along their entire length. It appeared that only the large number of knots kept them from splitting like a rail fence.

- The bolts in the metal fittings were large and few in number.

- Every bolt was clearly associated with a split.

I try not to remain in buildings like that very long.

;--

... okay, I'm getting to a point. I've often wondered if it's possible to reinforce a straight timber by wrapping it tightly in sheet metal, with no fasteners going through the wood, and the metal held in place by a good lockseam or a few Band-It clamps. Okay, I know it's possible, I'm just wondering if anyone has actually done it.

I'm also wondering what damn fool came up with the idea of using really big bolts to fasten timber framing, as if it were structural steel.





Mike Halloran
Pembroke Pines, FL, USA

 

[Dinosaur]

I recommend the book "Structural Design in Wood" by Stalnaker and Harris. This book discusses wood as a material before getting into the design issues. It also discusses connection design (and the problem of fastener size and arrangement) along with member analysis. A coworker of mine once told me that while most structural designs are based on bending and shear is later checked, in wood it is often the shear that controls. My dad told me growing up that in wood, it is all about laying out your connections. You have to have good connections or you get a bad design.

Getting back to your specific question, I recommend the idea proposed by SlideRuleEra but I would proportion the steel plates to carry all the load, and neglect the contribution of the wood after retrofit. Make sure to check your plates against buckling on the compression edge. This isn't quite a LTB problem and it certainly isn't an euler column problem, but you don't want those plates too skinny. Also, you may need a bearing plate at each end. Check the material at the ends of the existing beam and whatever they rest upon.

Good Luck

 

[kayah]

Another option would be to jack the beam and bond a strip of carbon fibre reinforcement to the bottom.

 

[corrosionman]

jrengineerMy very large ceiling was from 4 x 2 timber - - very flexible. To stiffen it for use as a floor we simply affixed a 4 inch x 3/16 inch flat steel strap to both sides of each timber using many many woodscrews. very easy and low cost.Now its as strong as a floor of 8 x 2 joists. Good LUCK CM

 

[nackra]

similar to steel angles and plates, we added C-sections on each side of long "clear span" that was easily accessible after demolition (series of jacks used until channels bolted in place)

a remodel job at my house: built temp wall to support roof trusses while we built custom dbl 2x10 w/ plywood filler (between 2x10's) to enlarge opening between rooms from 8-ft to 10-ft

Good luck