I-Beam Load/Span? - Page 2
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  1. #21
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    Machinery's handbook sugest 5 as a safety factor for structial steel if it has no unusual conditions like a moving load. I use that 5 number.
    Walter, see the original post, the application requires a moving load :rolleyes:

  2. #22
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    Randyc All good posts.

  3. #23
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    Wow... I don't know how to size this stuff but what I can tell you is that when I built my home shop I set up two 8" upright I beams. And later set an 8" wide X 8" tall I beam on the two uprights. The beam is a total of 29' 6" long across the shop. It is only bolted to the plates on top of the uprights. And I've had at least 5000lbs. hanging from the center with no exceptional deflection in the center. It did deflect some but that load was picked from one side and easily pushed slowly to the other without the load wanting to run away. I've also had two separate 2000lb. loads on it at the same time once.

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    Harley I am no engineer ,however that seems to be pushing it. Good luck

  5. #25
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    I'm beginning to think we need to get Michael Moore involved here, or some of the other members from the Bay area. They can keep an eye on the Golden Gate and let you know if someone decides to tear it down. It oughta have a beam somewhere in it that would be heavy enough to make everyone happy and safe

  6. #26
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    This site seems to cover the maths and has a nifty Excel download - but knowing the equations is the easy part of being an engineer. Knowing which is the right one is the tricky part.

    http://www.structural-engineering.fsnet.co.uk/steel.htm

    Regards

    Charles

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    Harley, to be technical, an 8" x 8" is actually a Wide-Flange, not an I-Beam, as there are no I-Beams with those dimensions. However, a W8x31 is exactly eight inches square, and may be what you have, or you have something close -- a W8x35 is 8.12" x 8.02", for example.

    If one does the math, you'd find that you're in very roughly the same stress range as one would be using my W6x12 example. So according to some, you should be dead by now!

    But seriously, I don't mean to dismiss the safety issues raised by other folks here. Those safety factors are very important, but if you're cramped on space, time and money, they can be put into some perspective. They are meant for commercial applications that are subject to lots of considerations that are not necessarily applicable at home, including daily use, fatigue over decades, protecting bozos from themselves, etc.

    There are a zillion hazards everywhere, and no shortage in a home shop. We all make daily if not hourly decisions, conscious or unconscious, about which hazards are acceptable and which are not, and different people will make different decisions given similar situations.

    Occasionally stressing a beam to 20-30ksi is not inherently life-threatening (as your experience illustrates), but if you passed on such a device to another unknowledgable person, you'd be irresponsible.


    As a final additional thought, I'd note something about I-beams vs Wide-Flange and failure modes. I-beams are much more dangerous that Wide-Flange when overloaded, because they are generally tall and narrow, and have radically different strength in the X and Y planes. So the typical faliure mode is not simply bending when the elastic threshold is reached, but instead they buckle, ie. twist sideways in the middle, and then bend like tin foil. For example, the S10x25 Matt cited has a moment of inertia of 124 in the tall axis, but only 6.7 in the narrow dimension -- in other words it is alomst 20 times weaker one way than the other. So when it starts to twist, disaster can follow quickly.

    On the other hand, the X:Y ratio of stiffness on Wide Flanges runs more typically from about 10:1 to 3:1, so you can design things that have much greater buckling resistance and will bend in the load plane long before they will buckle. As a somewhat gross genrealization, bending is a desireable failure mode (absorbs energy, gives warning, etc), and buckling is not.

    If you actually did load a 30 foot long 8" I-beam with 5,000 pounds, my gut sens is that it almost certainly would have bent and may well have buckled.

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  9. #28
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    If this is a free standing bridge crane remember the rating is different than a stationary I beam. A bridge crane has to be rated to withstand a certain moment of energy. I don't know what I am talking about but the engineers at work recently dealt with this and they were explaining it to me.

  10. #29
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    Wow.

    Lots and lots of good information. Once I sort through it all, I will be a lot closer to actually "engineering" this structure instead of simply "building" it.

    I especially appreciate the explanation of the terms used in Machinery's Handbook, and the education about the differences in wide-flange vs. traditional I beams.

    I did look at the gantry crane designs at grainger.com, and they seem to be underbuilt after reading all of these posts! My application woulld technically be more along the lines of a bridge beam or stationary gantry.

    Again, thanks for all of the information. My design and comfort level will be much improved as a result...

  11. #30
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    Whoa... sounds like I've come dangerously close to needing a new beam. An its prolly a good thing I've always been leary of standing under it with anything close to a Ton on it. I'm certainly going to have to rethink what gets hung from my do it all beam. It just does'nt sound like a do it all beam anymore.

    Sheesh.... thanks fer scarin the s?#t outta me.

    No really thanks for the insight guys. I had no clue I was pushin my luck that badly.

  12. #31
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    Harley, your beam doesn't particularly scare me (assuming it really is something like a W8x35), but it ain't no OSHA-compatible, do-it-all beam! However, I also would never stand directly under a 5,000 pound load on it, nor even a ton. But before I stand directly under anything, even 100 pounds, I think very carefully. There are often a lot more things to fail than just the beam itself. Whether you have 500, 5,000, or 50,000 pounds fall on your head doesn't make a lot of difference to you (does make a little difference to the clean-up crew!)

    Depending on if the height is convenient, you can always add a temporary column near a load to increase capacity (possibly dramatically). But you do have to be thoughtful about that too. A sufficiently overloaded column can buckle with almost no warning, and even being slightly off plumb can significantly reduce capacity. Column capacity is not as easy to intuit as beam capacity.

  13. #32
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    The deal with the length and buckling is the span to width ratio. That is given in Kent's also, with a table for derating over a ratio of 15.

    30 foot (approx) is a ratio of about 45 with an 8" flange, which is beyond the derate ratio. it goes up to 40. At 40 the derate is to 60% of nominal load.

    That is if there is no bracing. If linked to other beams, or restrained from twisting, the ratio is distance between restraints.

    I didn't run the numbers, but you probably were pushing it with 2.5 tons in the middle. You should have seen significant sag if it really were that much. Many structure applications are sag-limited, since sag breaks drywall and opens cracks.

    Of more concern to me is side restraint....what keeps your two columns from tippng over?

    A small side force can start a tip-over with a heavy weight on it. Harder to get out of the way, its like a big mouse trap.

  14. #33
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    I did'nt mean stand directly under the load itself. I was referring to the beam. I actually do quite a bit of rigging at work. Which is why I never really paid attention to the beam at home. Most rigging at home is for taking stuff off trailers and putting back on. That and working on equipment of my own. Most loads never clear 2' unless its smaller and I'm hanging to spray it. But this thread has brought a realization that maybe I should'nt be trusting my beam as much as I do. I'm used to having beams already in place at work that are known to be rated for the loads that we hang. At home I just figured the beam was overrated and never really second guessed it. The worst load ever put on it I did notice the deflection and kept the load close to the ground. We actually did take the time to measure the deflection just because we noticed there was some spring to the beam after rigging the load. All hung from heavy straps and 6T shackles. But anyway the deflection across the full 29' 6" was about 3/4" in the center. Can you tell me if that was terrible or just marginal. We estimated the load at just over 5000lbs. Can't really tell ya any more than the beam is 8" x 8". The only time I can ever remember picking a load over 2' was when I set a large safe up on machinery stands to spray it. I figure that was right around a 1000 and I was not the kinda person to leave a load in the air. Ie... the machinery stands.
    Can ya tell me anymore about the rating on my beam?
    Oh.... about the side stands. I used the beam beam material for uprights. Plated on both ends. I anchored the lower plates to the floor. Lag bolted the sides of the beams to a pair of 4 x 6 poles with 6 lags on each side aprrox. 5" lags. And then used 10' of 2x2x1/4" angle to make a center support from the center of the beam out from both sides. Lagged to each truss every 2'. I did that to attempt a little insurance that if any pull was ever put on the beam that it would not just tip over.

  15. #34
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    Harley did say "no exceptional deflection" One man's unexceptional deflection might be another's "run for cover"!

    Calcs say Harley should see 1.5" deflection under his described 2.5 ton load, assuming he has a W8x31.

  16. #35
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    This a little off topic.

    A year ago or so they were doing some construction on I-70 around Denver and were constructing an overpass. During construction they place a large beam on the piers (or whatever they're called) and apparently left for the weekend. I don't recall the exact dimensions but is was something along the lines of 48" high by 10" wide. Anyway during the weekend the wind came up and either bowed this long beam enough that it flipped over on it's side or the wind simply blew it over. In any case once it was down on it's side it couldn't even support itself and collapsed on the freeway, killing at least one person. To make this even worse someone that was familier with large iron beams had called the state patrol and suggested that this beam presented a significant hazard.

  17. #36
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    Harley, advising you on the beam means advising you on the right safety factor, which is subjective. If you apply the factors Matt suggested, 1400 lbs is your max load in the center (assuming W8x31), or conversely, if you want 5000 lbs, you'd need something like a W12x53 (12" x 10")

    To find out exactly what you have, measure the outer dimensions +/- 0.1", and for extra reference, measure the flange thickness +/- .020 (ie, use calipers)

    Personally, I wouldn't worry if I were you, but I would be conscious that 5,000 lbs is about as far as you should go; don't go there often or for long; don't go high; lift slowly and smoothly, and be extra attuned when you do it. All common sense that I suspect you didn't need anyone to tell you. Others might disagree, and I don't quibble with them.

  18. #37
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    No your right this has just been an eye opener. I now suspect that the safety practices that I do use may come have dangerously close to saving my [email protected]
    We always practice rules such as:
    Never, no exceptions do you stand under a load.
    As for the beam I still stand off to the side.
    Never lift it any higher than it needs be.
    Never leave a load suspended.
    No sub standard rigging equipment. That means no HB straps. My rigging equipment is the same rated stuff I use at work and it gets thrown away when worn just like at work.
    Besides I get a great deals on most of my equipment using cash on the company accounts.
    And most important of all...... follow your gut.
    I just wish I'd paid more attention to the load rating on that beam now. I'll be rethinkin what goes up from now on. Even worse yet I know two different guys using the same beam material only they both set their beams on 6x6 wood poles.
    Scary huh!

  19. #38
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    A 6x6 wood post taking 2500 lbs isn't worrisome. Wood has enormous compressive strength, and that's only 80 pounds per square inch. Think about taking a 1" cube of wood standing on end-grain and putting 80 lbs on it -- ain't gonna hurt it!

    The concern is bending, leading to buckling, so the issue is how long the 6x6 wood column is unsupported laterally. If the post were, for example, bolted to a concrete wall, not much worry. If it were freestanding 20 feet tall, well, don't stand too close!

  20. #39
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    Harley, also note that if at some point you want to improve your beam, you can do so in place. Just fixing the ends makes a substantial difference. All the numbers I cited were based on free end supports. If your beam is rigidly attached to the columns it increases the rigidity more than intuition probably suggests. Even more so if you create gussets. And you can strengthen the beam by things like bolting plates to be center web. All these things make for more much complex calculations, but with a little engineering and a bit of work you could beef it up probably much more cheaply than replacing it, all depending on the context of course.

    And even more simply, don't forget that you have much greater capacity away from the center. Maybe you can lift your heavier loads near a column.

  21. #40
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    While we're on the subject.... I'm building a 33' wide outside dim. garage that I want to span a beam across. The beam would have to be 32' 4" long,I have access to a 12" beam the right length with 5 " wide flange. Do you think this size would be adequate for my use? The most weight probably would be 2000 to 3000 lbs.This beam would be used only for hoisting, it's not part of the structure.


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