Reinforcing Wood Beam with Steel Side Plates 1

[NS4U]

I am reinforcing a wood beam with steel side plates. Are there any design provisions or design examples for this type of strengthening. I'm particularly interested in the requirements for the spacing of the intermediate connectors. From google, I've seen the typical spacing seems to be 16 in. to 24 in. but can't find a basis for this. Thanks.

 

[SlideRuleEra]

See the "Flitch Plate Beam" article in the June 2007, issue of "Structure Magazine":

http://www.structuremag.org/wp-cont...-Exp-Flitch-Plates-DeStefano-pac-5-10-071.pdf

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[NS4U]

Thanks, but this isn't a flitch beam. In my case, the steel is on the outside.

A flitch beam has steel on the inside. So, the wood side pieces prevents the steel from buckling.

 

[SlideRuleEra]

What are the dimensions of the steel plates? If they are really "thin", then many bolts or a wooden "cover plates" may be needed to keep them from "crumpling" under load. If they are "thick", then the fact that it is a "backwards" flitch plate beam won't matter - the principle is the same.

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[NS4U]

Thanks. I agree with you.

I guess what I'm getting at is what constitutes a "thin" vs "thick" side plate? And how do you determine how many connectors you need to prevent the crumpling?

 

[SlideRuleEra]

In my opinion, that would depend on too many variables such as plate size, thickness, beam deflections, etc. I would just make a five-layer flitch beam sandwich (new wood - steel - existing wood - steel - new wood).

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[KootK]

I'll check a horizontal strip of plate between bolts as a simple column and let that inform my bolt spacing. It may just be paranoia on my part but I've never felt too great about the ability of the outer wood plies to restrain steel plate local buckling.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Brad805]

I am curious what percentage capacity increase are you looking for? Mixing steel with wood tends to be my last resort (ie. removing column, gross inadequacy...).

 

[racookpe1978]

Are you planning on using structural adhesive between the two outer steel plates (try C - channels instead!) in addition to the spaced bolts?

What diameter bolts, what torque - how will you keep them torques as the wood shrinks?
How many bolts/length of the steel plates/channels?

What load and over what length?

 

[NS4U]

In case anyone is interested, I found my answer in a 1989 paper titled "Glitches in Flitch Beam Design" and in the 1956 "Timber Design and Construction Handbook". The answer is simple and straightforward, but the background and explanation is too wordy to concisely explain in this post.

 

[jwilki]

Is this a retrofit because of past damage or to increase capacity of an existing member? As other have said, I would also do a simple column check for buckling of a flat plate. Also plywood side plates are another good option if capacity/rigidity permits... very carpenter friendly

 

[KootK]

The answer is simple and straightforward, but the background and explanation is too wordy to concisely explain in this post.

Seriously? Serioiusly? You let us beat our brains out trying to help you solve this and, now that you have the "simple and straightforward" answer, you're not even going to tell us what the #$@&%*! it is? Best be shimmying you butt over to the scanner if you plan show your handle 'round these parts again in the future mister (or miss).

Did you get the "Glitches" paper from the Linda Hall library? I try to avoid that whenever possible. I hate waiting and receiving fax-ish looking things makes me feel like a cave person.







I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[NS4U]

lol