LVL or Steel Beam?

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Old 01-29-13, 11:22 AM
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LVL or Steel Beam?

At my cottage I am opening up the basement (to install a pool table) and removing a steel post in order to provide a wide open area.

The new span of the beam will be 16' and I am (was) planning to use either a W8-35 or W6-28 (with a 1/2" cover plate to give it a bit more strength) I-Beam.

I am sourcing the beam through a friend of a friend, but because that person is going on vacation for a month (would be nice!), I have to delay my project...

So I got wondering if I could use an LVL beam, or perhaps a couple, installed side by side, and spiked together to optimize the strength...

The advantages of thinking about going with LVL is the quicker availability and it would be easier (lighter and better to work with than steel) to install.

To maximize overhead clearance I need to keep the beam height to 8" max (which is why I originally went with a steel beam).

So my question is, is there a good solution to replace the steel I-Beam with an LVL and what dimensions etc would the LVL beam need to have?

Many thanks and regards.
 
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Old 01-29-13, 11:49 AM
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The only way to be sure is to go to a place that supplies LVLs and give them your needs, let them spec it out.

There may be some folks here that can help you out some or some online calculators...but you still need to go through the supplier/manufacturer.

Just a guess, but I don't think an LVL is going to work. Their strength is really related to their width. Just like 2 x 10 lumber is stiffer and stronger than a 2 x 8. Customer of mine who built a 2 story house had an LVL over a 16' garage door, IIRC it was at least 12" tall.
 
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Old 01-29-13, 02:42 PM
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Actually, gunguy, LVL strength is related more to depth than width. But his depth requirement (8") is the controlling factor.

A steel W 8 x 35 spanning 16' can support a single concentrated load (in the middle) of 15,600 lb., without a cover plate. Probably good for 20,000 lb. with a wide-enough 1/2" cover plate welded or bolted to the bottom flange. Is your living room furniture really that stout to require something so heavy?

By comparison, the Weyerhauser book I have shows a double LVL at 7-1/4" deep being good for a maximum bending moment of 7100 ft.-lb., which converts to only a 1775 lb. concentrated load in the middle of a 16' span.

It's obvious that steel would be a far better choice--almost 9 times stronger than the LVL, even without a cover plate. Especially if you can scarf onto a decent chunk of salvage stuff--saw a few 8" 20-footers on CL for $100 each a few weeks ago. Going rate for new bare plain steel is $0.75 a pound, plus some extra if you want them to cut it. A 16-footer would run you about $420 around here; I have never priced the shallow LVLs, so I couldn't tell you what you'll be paying for them (but I expect it to be well over $3 a foot for the double).
 
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Old 01-29-13, 02:58 PM
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Great info - Interesting and informative reading -thank you.

The extra strength (and I prefer to be on the conservative/safe side) is because the main floor above has a bearing wall which supports the roof, which also in return includes a hefty margin for snow load.

I am hoping my buddy's buddy will be supplying the steel beam at a good price!
;-}

It's starting to sound like I should stay with the steel beam and wait the extra time, rather than switching over to LVL...
 
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Old 01-29-13, 03:15 PM
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Bridge.....I used the wrong term...I meant the long number as in 2x6 vs 2x8. I was thinking width, thickness, length. Should have said height maybe?
 
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Old 01-29-13, 03:35 PM
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Being in Ohio, I doubt your snow loads amount to much more than 40 PSF. You might find by crunching the numbers that you could get by with something considerably lighter than a 35-pounder.

If you go with a W 8 x 35 steel, just remember that the thing will be heavy--in your case (without a cover plate) about 560 lb. Getting it into your basement and up into place on the permanent supports could be a challenge, unless you have a few strong buddies who work cheaply. Hint--don't open the beer until after everything is erected and the temporary supports are removed.

I built a roof addition over a fenced storage yard in Colorado a few years ago, and managed to install the 420-lb. salvage beam I bought from a scrap dealer without any help. The wife wouldn't believe me when I told it was a solo job when she first saw it in place--trick is to alternately work one end at a time, using leverage and a series of varying-height (temporary) blocks and a stout stepladder to get it up to the column tops. Wasn't it Archimedes who said that if he had a place to stand on, he could move the planet earth?
 
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Old 01-29-13, 05:27 PM
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BridgeMan45;

Sure sounds like you know your "heavy metal"...

I am told that I can use either a W8 or W6 (the later with cover plate welded to the bottom plate).

I appreciate your comments about the loading on the W8 and I would be thankful if you could also provide similar info on the W6...

Am interested to see how the (weight bearing) strength compare between the 2 beams - and if they are somewhat the same, maybe I'm better trying to get the W6 since it w/b easier to man-handle into place.

Cheers.

P.S. BTW, do you know what the deflection would be for these beams?
 
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Old 01-29-13, 08:59 PM
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Woo,

What's with the "cheers" thing? Are you a transplanted Brit or Canuck? Not that it matters, in the least. Just curious. My parents emigrated here from Europe, so I can't claim any "original" American heritage.

For your info, there is no such thing as a W 6 x 28--the heaviest 6" wide-flange rolled is W 6 x 25. Using the section modulus for it, the maximum concentrated load it would support would be 8350 lb., compared to the 15,600 lb. for the 8 x 35. I didn't go through the somewhat tedious comps for adding a cover plate to it, since 1) I'm lazy, and 2) I didn't know what size cover plate you would be using. And before going any further, keep in mind that all of my calculations include a comfortable safety factor, equal to the inverse of the yield strength divided by the ultimate strength, and then modified by the factor of allowable bending stress used vs. material yield strength. Or in round numbers, approximately 2.4 for A 36 steel. Meaning the flimsier W 6 x 25 could still carry a 20,040 lb. concentrated load before getting close to collapsing.

Maximum deflections for the 2 different beams are inversely proportional to their respective moments of inertia (I), and directly proportional to the maximum applied loads. For the 8", it works out to 0.62" (5/8") when the 15.6 kips are applied to it (which is not likely to ever happen in real life). For the 6" (again without cover plate), it works out to 0.80" (a tad under 13/16"). Even though the maximum applied load is a lot less, the deflection is slightly more because the section is not as strong (has a considerably smaller moment of inertia and section modulus). Keep in mind that the cover plate will decrease the larger deflection value above, considerably. Have I bored you yet?

If it were mine, I'd use the W 6 x 25 (or what you call a 28 lb./ft. member). Having 2" of additional headroom can be a blessing, especially when you and your buddies are carrying on, dancing wildly with pool cues sticking up into the air. Actual deflection will also be considerably less than the 13/16" because of the differences in maximum and actual applied loads. And having a total weight of "only" 400 lb. will also make it easier to move and install, compared to the 560-lb., 8" member. I'd go with a cover plate only if the applied loads absolutely dictated that such was necessary (or if it's a salvage beam with cover plate already installed). You might want to enlist the services of a local engineer to make the necessity determination.
 
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Old 02-02-13, 09:34 AM
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Again, many thanks BridgeMan.

On the "Cheers', yes I am Cdn, but I actually picked up the habit of using it from an Aussie friend of mine. Small world we live in!

Excellent info. Agree with you on trying to use the 6x25 (my mistake on the "28"...

And since a buddy of mine who owns a steel fabrication shop is agreeable to adding a 1/2"?? cover plate to help stiffen up the 6 incher it makes sense to go with the bit of extra strength. FYI, I was told that adding the cover plate would "kinda" put the 6" in a similar ball park to the 8" - put don't really know for sure...
- but it does seem logical that the cover plate will make the 6" somewhat more robust...

On a somewhat related topic, it seems a bit strange to me that adding a cover plate, welded to the upper or lower horizontal flange will be more effective than welding a plate to the vertical member (if you see what I mean) - in so far as it would be harder to bend (up/down) the plate when it is positioned on it's edge... ???

Am only waiting now for my guy to get back from hot, sunny Florida while I "chill out" in the great snowy frozen north !!!

Cheers - and all the best.

Glen
 
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Old 02-02-13, 02:08 PM
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All right, your teasing my "alleged" mind worked (about wondering how much strength the cover plate would add), as I was curious myself. I crunched the numbers for adding a 1/2" x 7" cover plate to the bottom of a W 6 x 25, using the moment-area method, with the following results:

Bad News: The additional weight will be 190.4 lb. if added the full 16', plus a bit more for the welds. Skip-welding is allowed, and actually helps to minimize distortion by lowering heat input--you don't want a curved beam, right?

Good News: The increase in Section Modulus is a whopping 68% (28.0 divided by 16.7), meaning the stiffened beam will be quite close in strength to a W 8 x 35--90% as strong, in round numbers. This also means that deflection under load will be considerably less than an unstiffened 6-incher.

The reason a horizontal cover plate should be on the bottom flange (yes, you want it on the bottom, and not on the top) is that the additional strength (Moment of Inertia, and subsequently, Section Modulus) is composed of a factor of the cover plate area multiplied by the distance 'squared' from the modified neutral axis. Adding the plate in a vertical orientation puts it too close to the neutral axis to make much difference. It's the same reason that all of those steel highway bridges you drive under on the Interstate have larger (horizontal) bottom flanges than top flanges--it's simply an economical way to make them stronger and stiffer.
 
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Old 02-03-13, 07:16 AM
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BridgeMan - WOW - you are amazing!

Really appreciate your hard work - which confirms that I'm good to go with a 6x25 with a 1/2" x 7" bottom cover play. And thanks for the advice on skip welding.

Interesting and duly noted that the cover plate adds the extra 190 lbs, making the 6 incher (with plate) weigh slightly more than the 8 incher! - but I guess that only confirms that in heavy metal there is strength...

It's going to be a bit of a challenge to wrestle all that weight into place but the methodical application of some jacks and levers etc should win the day. I rather enjoy figuring out a productive combination of using brawn and brain to resolve these kind of installations.

Am now really itching to get my beam and get it installed!

One last comment - think I'm also going to talk to my friend about maybe using a W 6 x 20, since it sounds like by using a similar cover plate I will still have lots of strength of my needs... - and this would save 80 lbs...

Once again many thanks for the terrific advice - really appreciate it.

Cheers, Glen
 
 

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