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  1. #41
    Join Date
    Jul 2006
    Posts
    1,508

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    Simple illustration:

    Take a yardstick place it on its edge with two pencils placed perpendicular to the yardstick, one pencil at the 1-inch point, and the other pencil at the 35-inch point. Place your pointer finger on the top edge of the yardstick at the 18-inch mark then push down. Which way will it move? It may go straight down a little, but it will move to one side or the other. That is exactly how a beam will fail under load. The wider / heavier the flanges are the more resistance to side movement / failure there is.
    Caution!
    These are "my" views based only on my experiences in my little bitty world.

  2. #42
    Join Date
    Dec 2009
    Location
    Williams Lake, British Columbia
    Posts
    722

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    And that's how that boom failed or snap in half, by pulling a load of trees side ways.
    The cylinder was actually the one that came with the loader from factory, my bad, he just had the hydrolics cranked to the max.
    Hard to believe the he used to lifted quads trailers that weight 17000 pounds to load them on the truck when they were empty.
    The boom was " where it broke" all 3/8 thick plates. Around 18 inches by 18 inches boxed.

  3. #43
    Join Date
    Aug 2004
    Location
    Milan Michigan
    Posts
    1,677

    Default

    Eric Carroll,
    I understand why you would question this, I too used to think about it as you do.
    I remember the first time that I had to go out to do a house beam reinforcement because the customer wanted to remove a column that was in the way of his new pool table.

    When the contractor handed me the engineered drawing showing me to weld a pc. of 1/2"x 6" flat bar to the bottom flange of the beam and then 2pcs. of 1/2" x 2-1/2" flat bar to the bottom sides of the top flange I thought ( WOW where did they find this crack pot engineer )

    Then another job came up and a different engineer had me do it the same way, I thought Wow the 2 engineers must of went to the same school.

    Eric, Where your way quits working is when you start seperating the 2 flat bars and add a webb. The top flat bar starts wanting to compress while the lower flat bar wants to pull apart verses bend and thats where the difference comes into play.

    For instance take a look at the bar joist in the big box stores.
    The bar joist is the same as a beam it has angle Iron for the top and a bottom flange and the webb which is the part standing up on end is nothing more than a diagonal round bar in many cases.

    You've always been told when building a header in a house that the pc. of plywood standing up on end between the 2" x ? gives it alot of extra strength that is not totally true, Its more for spacing it out.

    Another example is the boom on cranes like a Gradall for instance, You've probably seen some of these that have round circles cut out of the sides which would be considered as the webb.

    As some one mentioned in an earlier post the farther you move the material away from the center axis the more strength you get.

    I hope I was able to help. Portable Welder.

  4. #44
    Join Date
    Aug 2007
    Location
    arkansas
    Posts
    781

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    dang, i am jealous of that job! I live for those things!! 2 months ago, i came across a cat (mitsubishi) excavator boom that was cracked and splitting just under the base of the stick cylinder. the top and bottom are 1/2 and the sides of the boom were 3/8. plating the sides only gains nominal strength simply to help the boom from twisting under extreme loads... i.e. pulling up trees. plating the top and bottom is a must, as these things lift and lower, yeah? i gotta start taking pics of these major equipment screw ups that i repair. last year, it was a tele-handler (extendable fklft like a gradall or skytrack) made by cat. the brake was never set and it rolled face first down a mountain side and landed on the boom..... that one took me about 5 months to repair
    welder_one

    nothing fancy, just a few hot glue guns for metal
    www.sicfabrications.com

  5. #45
    Join Date
    Feb 2009
    Location
    Lodi, CA
    Posts
    1,223

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    Adding metal to the sides of a box beam, will stiffen the beam, not necessarily make it stronger. More likely, it will create a new stress point, for a brand new crack to start. Think about it a little, long and hard. I started many many years ago, doing "Hopto" beams. Don't know what a Hopto is???? Dam, I'm old.
    Obviously, I'm just a hack-artist, you shouldn't be listening to anything I say .....

  6. #46
    Join Date
    Dec 2009
    Location
    Williams Lake, British Columbia
    Posts
    722

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    If you fix a boom right it shouldn't crack where you fixed it, I have fixed boom for many heavy duty equipment that are still like they were the day I fixed them. If it's done properly, with the right materials and the right process.

    I've cut in halfs logging trucks bunks to take them from 8' 6" to 9' 6" the process was laid out by an engineer.
    I did it the same way as this boom by adding a boxed piece in the middle and fishplating them and none of them showed any cracks. These trucks were from a fleet that are inspected after every day of service.
    Tell you the truth I didn't sleep very well for a few weeks


    The reality is that when you make a fix like this on a boom of any kind it makes the boom stronger then when it was new. If it's done right of coarse.

  7. #47
    Join Date
    Dec 2009
    Location
    Williams Lake, British Columbia
    Posts
    722

    Default

    Quote Originally Posted by JSFAB View Post
    Adding metal to the sides of a box beam, will stiffen the beam, not necessarily make it stronger. More likely, it will create a new stress point, for a brand new crack to start. Think about it a little, long and hard. I started many many years ago, doing "Hopto" beams. Don't know what a Hopto is???? Dam, I'm old.
    What's Hopto

  8. #48

    Default

    Quote Originally Posted by Daniel View Post
    If you fix a boom right it shouldn't crack where you fixed it, I have fixed boom for many heavy duty equipment that are still like they were the day I fixed them. If it's done properly, with the right materials and the right process.

    I've cut in halfs logging trucks bunks to take them from 8' 6" to 9' 6" the process was laid out by an engineer.
    I did it the same way as this boom by adding a boxed piece in the middle and fishplating them and none of them showed any cracks. These trucks were from a fleet that are inspected after every day of service.
    Tell you the truth I didn't sleep very well for a few weeks


    The reality is that when you make a fix like this on a boom of any kind it makes the boom stronger then when it was new. If it's done right of coarse.
    If its done right the welded piece should be just as strong or stronger then if it was one solid piece.

  9. #49
    Join Date
    Dec 2009
    Location
    Williams Lake, British Columbia
    Posts
    722

    Default

    That's right, that's the reason behind root and face bend test to get certified for different position on multiple processes. Cracks show up you fail

  10. #50
    Join Date
    Feb 2009
    Location
    Lodi, CA
    Posts
    1,223

    Default

    Quote Originally Posted by Daniel View Post
    What's Hopto
    Warner-Swassey excavator, what they used to build this country before Cat, Case, JD, Hyundai, etc. excavators became common and popular.
    Obviously, I'm just a hack-artist, you shouldn't be listening to anything I say .....

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