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cadman

07:33AM | 05/20/99
Bvmisc
Hi all:

Was wondering if any of you have had experience with flitch plates added to an existing full length, (42') 3-ply, 2x8 beam to change span from 7 feet to 14 feet (remove column at 7' position) ? Size of hardware, spacing of same, staggered or double row, thickness and lengths of flitch plate(s) and material (angle, channel or flatbar), etc. ?

Please don't just tell me to see an engineer. I've inquired of a couple and they wanted $350-$500 just to come look, with no guarantees a design could be done which wasn't to combersome to install without a 12 man rigging crew, and jacking up the house to add an I-beam. If you know of design can be used (ie personnal experience), then I'll draw it up and bring in the engineer to stamp his/her approval on it.

My proposal:
Prior to removing the first column from the gable end of the beam, I intend to add two (2) 1/4" thk x 7" Wide x 14'-6" long, steel flitch plates, one (1) to each side of existing beam and bolted through with 1/2-13 x 6" bolts, (with flat and lock washers on each side), in thirty-five (35) places as follows:
1-1/2" in from each edge and 3" in from end, 12" o/c staggered spacing.

At each end would be a four (4) hole pattern (6" x 4"). Same pattern would be used on centerline of column to be removed. (All hardware to be tightened prior to removal of column.) ?? Torque ??

The plates will start at the gable end of the main beam and extend about 6" past the second column. I then plan to box-in the assembly with 1x10's on each side, suspended from the floor joists. I also plan to box-in the column, (square to the finished width of the boxed in beam).

To further enhance support, I can increase bearing support inside of the column "box", (floor to bottom of beam). I can also "pilaster" the gable end by adding supports off of the top of the exposed foundation, (about 4" wide, fluctuates due to form seams, etc.), lessening the span even more.

Not being a structural engineer, (but having had about 5 years of steel detailing/design experience in prior jobs), I "feel it in my bones", (however I don't want to end up with any broken bones if it all collapses), I will have the proper support required to remove the column. I live in Massachusetts where code is 40LL/10DL. By my figures, (please correct me if I'm making false assumptions or using wrong formula[s]), total load at section of beam to be "flitched" = 50 PSF x 24' x 14'** = 16,800 lbs. Since beam normally supports half the load, uniform load on beam = 8,400#. (Find lbs./inch =) 8,400# / 14' / 12" = 50 lbs./inch. which I need to support.
**{actually 13.92' [14.5' - (3.5" [gable end]) -3.5" [half length of column top plate])] }

Thanks,

Cadman

TomR

08:06PM | 08/10/99
Member Since: 10/10/98
34 lifetime posts
I have a couple of questions:

Is this a main support beam running down the middle of a basement, and you want to remove a column to make a bigger room? How may floors in the home, supported by this beam? How many columns from end to end? Which column are you removing? And what is the diameter of the columns? I am assuming by 3-ply 2x8, you are referring to 3 2x8’s nailed together, right. In that case, the sections are probably 8’ long.

I believe your load calculations do not take into consideration all the holes you will be making in the existing beam and what you call “flitch” plates. To clear span 14’, a 2-story house would typically use an I-beam 10” high by 6” wide, and holes would have to be limited to every 4’ or more, unless over a column. Your code may allow for a 8” high I-beam, with probably no holes in the span. A good example would be an W8x13 A36.

Typically, a “flitch beam” is one where a steel plate is sandwiched between two pieces of wood. The wood keeps the steel plate from twisting or buckling, and provides a good nailing surface. Holes would be limited to the ends, and for that reason only relatively short spans should be considered. Adding bolts in the middle to keep the sandwich tight would compromise the strength. Even though your design calls for 2 plates, they would be on the outside, so twisting and buckling would still be possible.

I have to say that my first impression of your existing triple 2x8’s tells me that they are already undersized for today’s code, but that may be because I do not understand what you have, and are trying to accomplish. Give me some more details, and I will try to help you out.

cadman

08:45AM | 09/15/99
Member Since: 04/20/99
1 lifetime posts
Hi Tom:
Please email me your email address and I'll supply you with some AutoCAD drawings I've done, relative to removal of column(2).

You can reach me at [email]kallbee@netscape.net{/email].

Looking forward to hearing from you.

Cadman

TomR

09:37PM | 10/18/99
Member Since: 10/10/98
34 lifetime posts
Sorry I took so long to reply. I have been working on the Bob's old BB lately.

My email is Rawcliffe@erols.com

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