I have read thru most of the posts on flitch beams, steel plate attached to wood beams.
I have a situation where I plan to remove a lally column in the middle of a 12 ft span in a basement. The column current holds up a triple 2×10 beam. I plan on attaching two 1/2 x 9″ plates on either side of the beam. My Beamchek program shows this giving me a L/750 Live load deflection. Plenty of margin and a nice stiff floor.
Found multiple references on this site and others that talked about bolt patterns and have settled on 1/2″ bolts 2″ in from each corner and 18.25″ OC 2″ from the top edge and 36.5″ OC 2″ from the bottom edge.
Now for my question for the experts on this site. Do I need to add a 2×10 to the outside of the steel on both sides. Or is this over kill.
Part of me says the wood is useful for prevent the steel from buckling, but on the other side, having the bolts bear on steel not on the outer wood may provide more stability.
Thoughts??
Replies
Flitch is a Waste of steel -- you are using 750# of steel , 60+ pounds per foot!
you could just bolt a single 9"X15#/ft C channel to the side, that's only 180#, you get the same strength, and better stiffness to boot. Plus, the whole thing is lighter and easier to get into place than just one of the flitch plates.
On the C-section, I'd use 12" oc both top and bottom, staggered.
Are the 2x10s continuous? If not, then a 9x20 C channel would be a better choice.
Heck, if you really want to bolt to both sides, 2 c-channels will be 1/2 the weight and twice the strength as the Flitch plates.
If you get the plates free or as scrap, the economics effect the calculations. If you gotta buy either the C or the plates at similar prices, flitch don't make $$$ sense.
You have some good points that are worth considering.
FYI, the plates only weigh 489# (UGH) but you are right the C 9 x 20 weighs about half that.
My calcs show the C 9x20 being equivalent to the two plates I had spec'd
The plates work a bit better since one end of this beam is in a concrete beam pocket and there is room for the plates to slide into the pocket directly.
With the C channel I guess I would cut off the flange on that end of the beam abit to fit.Hmmm. worth considering. Thanks for the ideasPS is there any concern with the structural element being off center from the bearing location. EG. the existing wood is bearing the floor joists and the ends and steel is offset by thickeness of the beam??
Junkhound,
Just one more data point. Got quotes from my local Steel supplier for both solutions.
Two flat plates = $287 total
One C 9x20 same length = $484Surprised the hell out of me I always thought steel was primarily priced by the pound. Maybe my supplier has some plate he wants to get rid of!!Thanks again for the thought. Love this site for bouncing thoughts up against the wall!!
Steel is traditionally priced by the pound (or tons), however these days rolled shapes are governed by availability. No one is stocking the items as much and there are only a few rollings at the mill per year. Shipping from foreign mills is pricey too.
...that's not a mistake, it's rustic
Edited 12/27/2006 11:49 am ET by BungalowJeff
You can't exactly "roll" your own, but how about welding?
-- J.S.
Not very cost effective, especially in the NYC area where welders time is more expensive than the steel. On big (really big) structures, fabricated elements are cheaper, though.
And I now have this image of an iron worker whipping out a pack of Bambu and rolling himself a beam. ...that's not a mistake, it's rustic
Two flat plates = $287 totalOne C 9x20 same length = $484
Wow! Over $2.00 a pound for the C channel!!! He must have to order it and is tacking on a bunch of 1-time special order costs. See what other C sections you can find, a couple of 8X8 C-section stair stringers would work well for your application. Or even look at a C10X12 or some such if you have the headroom.
The plate at $0.36/# is a nominal price, not a scrap price, but below retail.
I ALWAYS check the local scrapyard first before buying any steel retail (except for well casing, where it is illegal to use used steel - WA state)
Don't know your cash flow situation, but even though I'm super cheap I'm getting old and lazy enough that handling the weight and drilling 48 holes thru 1/2" plate vs 24 holes thru 1/4" or 3/8" web may not be worth saving the worst case $200 differential.
You could easily find a larger section for much less if someone has them taking up space in the yard. The support of excavation for a tunnel job I am running is designed based on the "I can get W36x135's at the lengths we need. Make them work."...that's not a mistake, it's rustic
Considering the challenge of drilling and lining up holes through multiple layers I would skip the extra 2x's and increase the # of bolts. I have installed flitch beams before to engineered specs and I seem to remember they always had a closer specing than what you are using, around 12" centers.But I have never used such thick plate either.I doubt buckling would be a concern.
Also I just remembered that an engineer also specced minimum sized washers as well.
cheers Rik