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  • DSW
    replied
    Thanks, I'm not sure I quite undersatnd it all right now, its been quite a while since I had to do and of the structual calcs. I used to have a great set of notes that listed all my comonly used formulas and the coresponding diagrams but I may have loaned themto someone a while back. I'll have to dig out my books and read up on some of the terms and crank a few numbers out. I'll also have to see if I can lay my hands on the AISC manual and take a look at the pages you recomended.

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  • Bodybagger
    replied
    Lrfd

    M=PL/4
    P=2tons=4000 lbs
    L=5'
    so M=5000 ftlb

    1/2 load on each beam
    so M=2500 ft lbs
    LRFD load factor for live load =1.6, so multiply by 1.6 for 4000 ft lb=Mu
    (often 100% impact factor is assigned, but loads would be moving over at low speeds, so there is no additional impact factor)
    Mu= .9 Mn

    Beam is supported throughout from lateral torsional buckling due to the L-angle crossmembers, so use phi*Mp as max moment for each section.

    AISC manual 13th ed. lists phi Mp as max allowable for those sections (table 3-8, page 3-88) as listed in previous post. I agree it would be overkill, but then again it does include a large factor of safety.

    I just used the tables instead of going through the maximum plasic moment calculation from the section shape properties. AISC has already done it for me and listed the results at the bottom of the page under "beam properties."

    On a side note, ASD method allows the same beams. But on larger sections, there are a lot of cases where LRFD allows and ASD calls for bigger beam. The new method is more economical sometimes, but the results are often the same.
    Last edited by Bodybagger; 03-01-2008, 10:55 PM. Reason: added ASD note

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  • DSW
    replied
    Bodybagger I'm curious as to how you came up with your moment calc.

    [QUOTE=Bodybagger;140007]You want each ramp to hold 2 tons, and they will be 5’ long.

    Assuming 5’ long ramps, worst bending case is 2 ton load right in the middle, which is a bending moment of 4000*5/4=5000 foot pounds. If it’s built with a C channel on each side, each channel gets 2500 foot pounds Using a load factor of 1.6 for a live load, this becomes 4000 foot pounds ultimate load.QUOTE]

    It's been awhile since I did my structural design class and I can't locate my load design calc table however... What value are you using for S. My only table for chanel lists S values not Mr. If your Fb is 24 and S= M/Fb I get a value of .208 for S. Wouldn't you also reduce your load for the angle, or are you just assuming worst case load if flat? Bear with me, if I can just visualize it it'll all make sense again. 4" chanel just seems heavy compared to whats on our 10ton tag along trailer. Its at the shop for inspection right now so I cann't run and measure.



    Ranchersam 2ton per ramp may be a tad over done. My F350 has a front axel rated at 6800lb. I find it a little hard to see 8000lb on the ramps at once. Whats the GVW for that trailer? Your ramp load is 80% of max load for a 10,000 GVW trailer! Not that over building is a bad thing mind you. Safety first. 5' ramps may be a little long unless it is a deck over wheel trailer.

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  • ck welding
    replied
    My truck weighs about 6000# or so. I made these from 2x4x.120 and 2x2x.120. They don't deflect at all. Remember, strength is in the vertical direction, so going with wide, thick stock is of no advantage.



    lots of pics here:

    http://s128.photobucket.com/albums/p...ler/?start=all

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  • Bodybagger
    replied
    You want each ramp to hold 2 tons, and they will be 5’ long.

    Assuming 5’ long ramps, worst bending case is 2 ton load right in the middle, which is a bending moment of 4000*5/4=5000 foot pounds. If it’s built with a C channel on each side, each channel gets 2500 foot pounds Using a load factor of 1.6 for a live load, this becomes 4000 foot pounds ultimate load. The LRFD value of allowable bending moment for a standard channel supported throughout is:

    C3X3.5=3340 ft lb NO GOOD
    C3X4.1=3570 ft lb NO GOOD
    C3X5 =4100 ft lb OK
    C3X6 =4700 ft lb OK
    C4X4.5 =5730 ft lb OK Also the lightest section, and stiffest.

    BTW, if you are unfamiliar with the notation, the second number is the section weight in pounds per foot. Just pair two up 24" apart and weld angles back and forth across the top, and stiffening angles across the bottom at 6 inch intervals. These will safely carry your 2 ton wheel load, and the flimsiest one that meets the criteria will only sag 0.168" under 2 tons.

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  • aametalmaster
    replied
    How about 3" channel and the angle cross bars with 1/2" flat plate for the hinge with a 1" bar for the pin. Thats how i did ours...Bob
    Attached Files

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  • ranchersam
    started a topic building trailer ramps

    building trailer ramps

    Hello all,

    I'm planning on building ramps for my 16 ft pipe utility trailer. I want each ramp to be at least 2ton capable. Does anyone have specs and or pictures of theirs? I want to make each ramp 2ft wide. I'm thinking 3/16" 3X3 angle on the sides and 2X2X 3/16 braces every 6-8"? The trailer deck is about 18" from the ground, so I'm thinking ramps are 4-5' long. As to attaching the ramps to the trailer, it'll be with hinges on 3/4" round stock attached to the trailer at 4 points by 1/4" flat stock . Can you buy the hinges? I'm trying to watch the weight but build the ramps strong at the same time. All guidance appreciated.

    Sam
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