5-ply LVL beams 1

[NFExp]

I was wondering if anyone has used 5-ply LVL beams for previous projects. I have a project where I recommended a 5-ply 1.75"x16" LVL beam. The beam is 23' long and loaded mostly from the top and a little side loaded. I have specified the beam to be bolted with 2 rows of 5/8" bolts.

The contractor told me that the manufacturer does not recommend this and that the warranty would not be valid.

Any thoughts?

 

[XR250]

I have done it. Don't see why it won't work as long as the shear is transferred properly with the bolts.

 

[BAretired]

Loading on top should not be a problem. Loading from the side is not recommended, but it depends on the magnitude and symmetry of the side load. Talk to the manufacturer about his warranty; the contractor may be mistaken.

BA

 

[msquared48]

Sounds like an awfully narrow beat for a 23 foot span and 16" depth. Must be very lightly loaded.

Mike McCann, PE, SE (WA)

 

[pmtrevisan1]

Don't forget about blocking to prevent buckling.

But i have done that on several occasions, as previous posters i would not do this for heavily side loaded members. For mostly top loaded it is a non issue as long as the boltIng is sufficient for the 5 plies to act as a unit.

Pmt

 

[TehMightyEngineer]

Can be done, make sure the contractor can get the plys in place one at a time. Otherwise they will hate you forever as the weight will be way too much to move into place without some equipment being involved.

Maine Professional and Structural Engineer.
(Just passed the 16-hour SE exam, woohoo!)

 

[dhengr]

NFExp:
You do mean 5 members, 1.75"x16" LVL’s bolted side by side, right? That’s an 8.75"wide by 16" deep beam, right? Must be pretty heavily loaded. Is this a new beam, or a couple side LVL’s added to an existing 3 ply beam? And, don’t forget the applicable adjustment factors, long term creep for example. The primary issue probably is how effectively you transmit/distribute the total load, equally, to all five members making up the beam. And, the LVL manuf’er. probably has some doubts that that gets done properly or adequately in many cases. Take a look at the NDS or any good Wood/Timber Design text book for how to design a doweled/bolted connection, and their different modes of failure. We have a fairly good understanding of two and three member connections, but it get a little fuzzier when connecting five members. And remember, that the member must deflect/move a bit to really bring the bolts into bearing in the holes. Also, driving a bolt through a nice tight hole 8.75" long is a trick too. Do you really load all five members essentially equally? If most of your load is from the top and you truly do apply that to all five members, that’s good. But, remember that two joists spanning from opposite sides will tend to overload the outer ply by the very nature of their own deflection and curvature. Side loads from joist hangers and the like really must intentionally be carried into the inner plys by the design and implementation of your bolted connection. In trying to finesse this detail a bit, I’ve actually held the outer plys 1/8" to 1/4" lower than the inner three plys. This causes the first inner plys to be loaded and then the bolts are forced to distribute loads through fewer plys, but both inward and outward. This sorta replicates the three member failure mode. Another reason for this detail was that I didn’t want to shift the bearing area out from under the end verts. on existing 2x4 wood trusses.

 

[woodman88]

The warranty is still valid as they only cover the LVL, not how it is used. As for doing five ply beams, they state that they "require special consideration by the design professional" per the attached pdf.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[XR250]

My experience with LVL warranties is that they are pretty much useless anyway. I have probably called them to look at a excessively sagging beams 5 times over the years.
In all cases, they claimed they were put up wet.

 

[SAIL3]

I do not believe I could guarantee with sufficient certainty that all 5 plys were activated in resisting the applied load unless I span the 5 plys with a conn @ the point of the applied load designed to spread the load initially to each ply.

 

[XR250]

Assuming a 700 plf load (about all I would use on a 5-ply 16 spanning 23 ft) and assuming it all goes to the center ply (conservative), you need to transfer 2/5 x 700 = 280 plf to the next ply over (on each side of the center). That is (3)10d @ 12" O.C. Then you need to transfer 1/5 x 700 = 140 plf to the extreme outer plys - which is about (2)10d @ 12" O.C. Add bolts to keep the whole thing together and use more nails and you are done.

 

[woodman88]

As ExcelEngineering states, I would use nails and bolts or wood lag screws maybe Simpson SDS wood screws. The problem I have with just bolts is that you have to oversize the hole to get the bolt in which requires greater slip before the bolt transfers shear load. Attached is a link to Simpson information.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.