Strength Reduction: 1 continuous 20′ LVL beam vs construction of a large beam with smaller segments
user-7513326
| Posted in Construction Techniques on
Hi
I would like to install a beam that would span a 19′ 7” opening to hold weight of ceiling (no roof load). It would be easier to construct a 20′ 7″ beam by assembling it with smaller LVL segments than to install a continuous beam, but I can’t find any information about whether this technique is acceptable and how much bigger the beam has to be in height or width to accommodate any weakness that smaller segments would create compared to one continuous beam.
Option 1: two 2″x 16″ x 20’7″ LVL beams fastened together
Option 2 Three 2″x 16″ x 10’3.5″ LVL beams, plus two 2″x 16″ x 5’3.5″ pieced together to create the same beam dimensions as option 1 (staggered seams).
Replies
Sounds like over kill for just a ceiling load. What is the tributary area on each side of the beam?
What is the ceiling joist span?
The joist span is 24 feet from exterior to exterior wall. The beam would sit at about 10 feet in from one of these walls. The joists are 2x6 at 16 inch on center spacing.
The real question in my mind is whether I can create a larger LVL beam with smaller segments. See attached for what I am proposing.
We did very similar with a cathedral ceiling beam. Was easier for me to not have to hire a large crane. Closest road on steep hill was too low trees to get crane back there, and doing it from front would have been a huge crane. Neighbor did that on $5m house, and it was letters mailed to everyone and crane permit process.
Ours was done with 3x LVL 2x14? and around 25' long. easy for 3 people to do from ladders. Was a sandwich with staggered end joints. We did a total of 4x of them in various places and sometimes with only 2x.
I calculated and got easy signoff from our engineer and city, since Weyerhaeuser has all the relevant data. You need to use SDS screws (get an impact driver) in a particular pattern.
https://www.weyerhaeuser.com/woodproducts/document-library/document_library_detail/tj-9000/
Putting joist hangar nails into the LVL was a pain for the long ones. used a palm nailer.
Doing it again, would use the SD Connector screws. Did the entire deck with those.
https://www.strongtie.com/strongdrive_exteriorwoodscrews/sd_screw/p/strong-drive-sd-connector-screw
Great information Allan. Thank you.
If I decide to go with 3 Lvl beams fastened together to allow the use of lower height LVL beams (three 14” instead of two 16”), do my posts have to increase in width to match the wider beam?
we used the really beefy simpson connectors (I'm not a simpson shill, really).
https://www.strongtie.com/columncaps_capsandbases/category
they had them in a very wide variety of flavors to support just about anything to
anything, including for both dimensional lumber and engineered PSL/LVL.
you put them in with those ubiquitous SDS screws (and predrill a pilot)
most of the posts we had ended up 4x6 PSL to support compressive load,
but there are standards for buckling and compression on these that will determine
what you use. (on longer posts buckling might be more important)
We're in highest earthquake zone and 3 months of earthquake insurance would be
more than all the upgrades, so the peace of mind is worth it. I also won't be trying
to hire after the big one when labor will be non-existent.
I'm a non-practicing mech.eng, not a civil, but most of these are done with rules of
thumb and tables. Go through the weyerhaeuser book and see if you can find the
right situation, add up the tributaries, and size it. Then pay an engineer for a couple
of hours to make sure it was right, even if he's not stamping plans/permit. from my
standpoint of view, I was getting the benefit of his very expensive engineering
degree and 20 years of experience for a couple hundred bucks.
My first engineer was old fashioned & spec'ed everything out with 4x6 plain lumber and
things like 4x12, but finally found someone smarter.