Reinforcing an existing LVL-Flitch Beam 1

[sanford1]

Hello,
I have an existing 25' beam consisting of (2) 1.75”x11.25” LVL engineered wood beams with a ¼” steel flitch plate sandwiched between the LVLs. The beam has a few (basically none) small carriage bolts holding it together. The beam has been in place for approx. 10 years and is starting to show signs of rotation / torsional buckling and moderate deflection. Calcs are showing that two 3/8 plates would need to be added and throughly bolted, however drilling the existing beam would be labor intensive. Widening the beam a great deal will be difficult due to an existing door and window on each side of the support column. Adding a mid-span column isn't an option.

Does anyone have any suggestions on alternative designs to tackle this problem?

Thanks

 

[manstrom]

I'm not a fan of flitch beams because they either aren't designed properly or installed properly. Some options:

Weld a plate to the bottom and angles to the top, effectively creating an I beam (built-up girder) Ditch the LVLs (I would be surprised if they were continuous anyways)

Pull it all out and replace with a steel beam

Pull out the LVLs one at a time and replace them with C12s, steel plates or MC 12s or similar.

Of course, brace the beam before you do anything drastic.

 

[BAretired]

If you have a little depth to spare, you could use a rod and turnbuckle each side of the existing beam. Attaching them at the ends of the beam could be a bit tricky if you don't have access to the ends of the beam but might be possible with a piece of specialty hardware and a few glulam rivets.

Or you could build a pair of steel trusses in place using angles for chords and flats for web members. The bottom chord could turn inward but the top chord would project outward.

BA

 

[FSS]

Look into Simpson Strong-Tie TB Screws. They are supposed to be self-drilling and should have no problem going through the 1/4" plate. Not sure about the 3/8" plate though. Maybe use them coming in from each side? There might also be self-drilling screws with longer lengths elsewhere.

 

[hokie66]

My preference would be to plant a channel on one side only. I don't see drilling through the existing to be a big job.

 

[Archie264]

Hokie, why only on one side? Just curious.

 

[hokie66]

Archie,

Just to make it easier on the workers who have to install this. I am just thinking about how I would do it if in my house. A channel is a much more efficient bending shape than a plate, and surely an appropriately sized channel would do the job. Another advantage of a channel is that its shear centre is outside the web, so eccentricity should not be an issue.

Probably the best reason to use a member on one side only is to avoid the difficulty of matching holes on both sides. The holes in steel side members would be punched in the shop, and it is very difficult to align two pieces and drill the holes perfectly in this arrangement.

 

[Archie264]

Wow, all very good points. There's a lot of foresight and practicality there. Thank you.

 

[msquared48]

You may need to shore the joists, remove the existing beam and install a new steel beam to get the deflection limits and performance you need.

Mike McCann
MMC Engineering

 

[connect2]

What are everybodies opinions on the currently deflected shape of the LVL Beam and the attachment of new steel plates. Should the deflection be removed, ie the beam jacked up, before the plates are installed? Or does it matter. What amount of deflection is anticipated for the new beam?

 

[Robbiee]

This is similar to BA's second suggestion.

 

[RareBugTX]

I like BAs idea, its good for contractors to work with, i would like to consider the attachment of such chords and diagonals to the existing lvls. The bottom chord would be to start with already in tension and it may require a deeper angle section and leg depth for the bolts to attach. I would definitely look into jacking it up on installation and provide camber.

 

[dhengr]

You have to clamp the old beam back together to facilitate the drilling and bolting. And, you do want to jack it up, so it actually has camber up prior to applying your reinforcement members or doing any drilling and bolting. That way, when you release the jacks the existing beam will redistribute some of its load to the new reinforcing members, and they will more immediately start acting in unison. Without the jacking operation, the existing beam will have to deflect even further before it starts bringing the through bolts (and bolt holes) into play and finally starts loading the new reinforcing members. You calculate the final deflection of the combined member, and can calc. deflection and camber on the existing beam to estimate the load transfer. You might want to hold the new members down 3/16" at the top so that any vert. movement does not start screwing around with joist or truss bearings.

 

[kipfoot]

If there's a wall or more flexible space above this beam, could you consider a new beam one level up with a hanger to support the flitch beam. I wouldn't need to be in the same plane as the flitch nor would it have to be at midspan.

 

[XR250]

@Hokie

Many shops use magnetic drill presses to drill the holes so they could just stack the plates and get them to align.
I agree. Drilling thru 1/4" plate is easy with decent, sharp bits. Get a Drill doctor to keep it sharp.

 

[hokie66]

Excel,
There is no problem in matching the holes in two pieces of steel in the shop. The difficulty I was pointing out is that it is very difficult on site to maintain the drill alignment perfectly so as to hit the holes on the opposite side when there is a member sandwiched between. For example, drilling holes in posts which are set in a stirrup is tricky, usually resulting in a bit of reaming and drilling from both sides.

 

[shobroco]

Jack it up as suggested & clamp the existing beam back together. Then use powder-activated pins (Hilti or Ramset shots) to stitch the existing pieces together the way they should be (LVL TO steel). Add a channel as hokie66 says, with pre-drilled holes in it & screws into the single LVL only. Assuming you can calculate the necessary forces to be transferred & the fasteners to do so, this is not that tough to do.

Too many people try to make things more complicated than they are.

 

[connect2]

How successful has anyone been jacking up the beam to 'remove the deflected shape'? We have found that first off you're looking at strengthening and stiffening a wood beam with flitch plates because it's in shape it's in. we have found it difficult because the deflected shape of the wood beam is more or less permanent ie it has over time creeped into that shape.

 

[shobroco]

You jack it to take the weight off while the new connections and members are installed, then remove the jacks to load them. Without jacking, the remedial work does not do anything until the beam deflects further. Whether or not you can remove an existing unsightly deflection is a different problem than increasing the load-bearing capacity of the member, which is the concern expressed in the OP.

 

[connect2]

Yes I understand that re purpose of unloading existing beam. My question was more about long term creep deflection of wood/timber members. When you have for instance an 8" x 16" wood beam 16' long with a 2 in deflection that has been there for 60 plus years as an example what thoughts does anybody have on getting the deflection out? And how much deflection would you try to get out? All? Half?