Connecting steel plate to wood beam - Composite Beam

[bigmakattak]

Hi,

I want to move a post in the basement to make a clear span of 17 feet for the main floor beam. It is (3) 2 x 12's now with a 12' span. I have calculated to the point of figuring the plate to be 5/16" on each side but will use 3/8" x 10". I have calculated max shear of 5.9K, max moment of 26 ft-k. with a load of 675 plf. Properties: I(transformed) 1943 in fourth, A (transformed) 184 in squared, and S (transformed) of 345 in cubed.

I want to bolt through the wood to connect both plates and the wood and have them act composite.

How can I determine the spacing and number of 5/8 inch bolts? Plan to stagger them vertically on the 10" plate.

Also any tips for checking bearing on the wood wall columns made up of 2 x 4's would be helpful. Can transformed area be used in the bearing calculation?

I am a rusty old Civil Eng. not structural.

Thanks,

Bigmakattak

 

[msquared48]

Look up "Flitch Plate Design" on the internet and see what comes up.

One thing to check - are the 3-2X's continuous over the new 17 foot span, or spliced? If thy are only 12 feet long, it might be easier to shore the joists and install a new upset glulam or microlam beam after the 3 2X's are removed rather than use the plates.

For the bearing, just use enough 2X4's to limit the bearing stress to 400 psi or so.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[msquared48]

I saw from the net that StruCalc 6.0 and above does flitch beam design, and they have 7 day trial downloads... Just a thought.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Lion06]

Here's an article.

 

[bigmakattak]

Thanks to all this looks like exactly what I need with the Flitch design. I will check it out and run the numbers. I have a good source for plate but like the new member idea as well.

With regard to the bearing, the transformed steel area with an N of 19 makes up a large amount of the bearing dimension as opposed to the wood portion. The steel plate will be supported on the column but in a sense it would seem like the loading is highly concentrated in the steel plate at the bearing point. I would like to ignore the plate contribution in the bearing calculation but will exceed the 400 psi. Also, I would need to tear apart more wall (which I may have to do) to enlarge the column cross section. Just wondering if it is common practice to used transformed area in the bearing calc.

Thanks.

 

[BAretired]

Another method is to use a steel channel each side of the wood beam and ignore the contribution of the existing wood. The channels are placed tight to the underside of joists.

Bolts through the wood beam must be adequate to prevent lateral buckling of the channels. Bolts at the ends must transmit the full reaction through the wood beam over the post unless the channels are otherwise supported.

BA

 

[MiketheEngineer]

Not sure if everyone does this - but with the 2x12's being cut - I basically ignore them for any moment capacity. Any help they may provide is an "extra". I beleive most flitch plate calcs or software assume continous seteel and wood members - which you no long have.

I design the steel plate to carry the total load and check deflection. A rather easy calc.

I bolt or lag to the remaining 2x12's to provide lateral stabilty to the steel plate, carry the shear at the ends and provide the bearing area. Go to the NDS for caculating shear allowable and bolt/lag patterns.

While you are at it - you may gently push up on the existing 2x12's to take any deflection or sag out of your existing floor. BE CAREFUL doing this or you could open up the cracks you have so carefully fixed over the years.

 

[msquared48]

As Mike alluded to, the flitch plate design is not really what you need as the 2X12's are not continupus through the new 17 foot dimension. If you were just reinforcing the 12 foot span, then yes, the flitch plate would be useful.

You really should just install another continuous beam of your choce of material and ignore the existing 12 foot section as Mike suggested.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[paddingtongreen]

This would probably be anathema to most structural engineers, or at least engineering heresy, but the supports are needed while the building is being constructed; but once it is up, it has wall studs and drywall diaphragms that act with floor joists and flooring and ceiling diaphragms to provide very deep, very strong girders.

I've seen the column at the center of a basement removed with no further measurable deflection of the floor, immediately or after a month. I bet there would be, but I lost the bet.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[MiketheEngineer]

While "paddingtongreen" brings up some interesting points and some do hold truth IF this, IF that, IF eveything works as he suggested. And just wait until they have a PARTY and dozens of people show up - not just the two people who live there.

But I have seen way too many floors sag that were designed "almost" correctly except they were a size too small or they didn't check the theoretical beam deflection - WHICH was just about on the money!!

Also have seen a house (under construction) that practically collapsed because the plumber cut through the floor beam and then the drywall crew unloaded on that floor.

Also saw a roof - designed by the homeowner - that DID collapse when the roofers attmpted to re-roof. Thank god it fell about an hour after they randomly placed the new bundles of material. 2x4's spanning about 18' !!!

Fix it....

 

[msquared48]

And as I have mentioned in the past here, I have seen 100 year old 2X4 exterior studwalls with the sheathing removed behyave as a Vierendiel (sp) truss - sorry, but I can never spell it correctly.

The result was to put more load to the tip of a steel cantilever beam causing unanticipated tip deflections due to the lack of backspan loading. Only time I have ever seen it in 40 years of structural engineering exoerience.

We cannot always call it correctly the first time. The trick is to know why it was wrong and correct be able to it.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[bigmakattak]

All of the comments are much appreciated. I do have a splice (non-continuous 2 x 12)in the new span so glad that was mentioned. I was actually thinking of adding a long plate to the bottom and lag screwing it in. That would provide some tension strength to the bottom. Not sure if top of that particular 2 x 12 would provide compression though. Seems like it would be cobbing it up a little too much.

Paddington has some good points but would rather leave all of that as factor of safety as opposed to depending on it. I think that is what he meant in his comments. The "engineer" on the block does not want to give the neighbors something to talk about you know!

Anyway I got what I need with all of your help. Thanks a bunch and hope to help out in the forum in the future as well.

 

[vandede427]

i was talking to a person yesterday who kept calling it a "flinch" plate. i think one time they said "finch" plate.

 

[PT999]

As per the DeStefano example
Does anybody know the corresponding NDS value for 5/8 bolts

 

[msquared48]

Van... There is such a thing that they use to construct houses for Finches.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[MiketheEngineer]

NDS bolting patterns must be checked 4 or 5 ways - bolt failure, single/double shear, wood failure a couyple of ways, angles of wood members, etc.,etc.,etc.

Get the NDS book and try to muddle through or a good text showing how to do it. OR even better a piece of software you trust....Maybe Engineering International.