How do I calculate loads on poles and guy wires?
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  1. #1
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    Default How do I calculate loads on poles and guy wires?

    Guys its been too many years since I had to do this basic math.
    Is there a simple way to cheat to get the loads on all the guy wires and poles in the diagram below?

    screen-shot-2019-11-09-9.14.33-am.jpg

    That would be with all the lengths and angles filled in of course.

    Online calculator...?
    Oh- I realize the longer arm on left would cause the structure to fold over in that direction- a static model or perhaps with load increased on right to enough to balance.

    Thanks all

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    Ok- looked around and I think the guy load is a simple question.
    This:

    rope_angle_increased_tension.jpg

    And I suppose that the upright poles are somewhat less than guy load..

    Edit-
    Oops....
    Not somewhat less... more- much more..

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    I don’t mean to be sarcastic at all but without knowing what that is for I think you need to hire an engineer. There are way more questions in that diagram than guy wire loads.

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    I don’t think it will be a problem- I was hired by the city of Burlington VT to build a roadway bridge- the white bit in middle is a reinforced concrete slab- anyone know how to pour that?

    (the specter of sarcasm got away from me...)

    This is just a tent frame- I want to make sure that the uprights which are 1-1/2"x1/8"x3'-8" 6061-t6 aluminum tube stay in column.
    The horizontals are robust enough that I am not worried that they will yield under the compression loads.

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    Statics problem.
    Need to calculate a Factor of Safety.
    What is your exposure in the event of a liability- accident?
    Talk to your insurance agent about covering your........tail.

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    Quote Originally Posted by Trboatworks View Post
    ...I was hired by the city of Burlington VT to build a roadway bridge- the white bit in middle is a reinforced concrete slab- anyone know how to pour that?
    How the Hell did you get a contract to build a bridge without a full engineering workup? How can you even price
    something like that without knowing what materials you need to use? Are they gonna sign a waiver absolving you
    from all responsibility if the the thing fails? Doesn't have to fail catastrophically, just a little sag-enough to render
    the bridge unusable--could cost a small fortune to repair and/or replace.

    No disrespect to you but you're either dealing with some very dumb people or there's a lot more to the story. I'm
    all ears...

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    Quote Originally Posted by jhruska View Post
    Statics problem.
    Need to calculate a Factor of Safety.
    What is your exposure in the event of a liability- accident?
    For own use- negligible exposure.

    I found this site to throw some numbers on tube sizes:

    Calculate Required Tube Size Using Structural Properties | Allied Tube & Conduit | Mechanical Tube Division

    Seems the 44" stick of material can be 1-1/2" in .035" and easily beat the load.

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    Couple of questions. The white slab. Is that a solid like a slab of concrete? You will need more information regarding the poles since in the lower ones there is a bending and compressive load and the verticals a compressive load that might cause buckling. Is there a reason that the guys are attached to the horizontal poles at the load point of 500#?

    Otherwise a simple problem. Sum of the forces in the X = 0, Sum of the forces in the Y = 0 and sum of the moments about any point = 0.

    Tom

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    Yes- white is solid structure.
    Guy have to be attached at outboard ends of horizontals.
    Bending is met on horizontals by beam size and the load is not point as shown- distributed load.

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    There is not nearly enough information given to allow even a wild assed guess of the loads. Find a structural engineer with experience in small bridges and furnish him ALL the relevant information.

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    Quote Originally Posted by Trboatworks View Post
    I don’t think it will be a problem- I was hired by the city of Burlington VT to build a roadway bridge- the white bit in middle is a reinforced concrete slab- anyone know how to pour that?

    No direct experience with concrete bridges but I have done plenty in multi-floor buildings with concrete floors. Upper concrete floors of buildings are poured on top of shoring designed for doing that. They are smooth plywood in aluminum frames on top of adjustable aluminum poles and bracing. The one I did work on had a floor something like 14-16" thick. (2nd floor of a hotel) 4 more floors of wood on to of that.
    Here is one system: Dropshore Concrete Shoring | Gamco Inc.
    Pan decking is a more common way but leaves the steel pan on the bottom of the concrete.

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    Doh....how to over react....its just a tent frame,dummies......I say go with 3/16" dia S/S wire for the guys ,and it will be plenty strong enough......you obviously know all about wire fitings,so just go for it.

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    Need lengths of beams and cables. Need lengths to point of attachment of the vertical struts to the horizontal member.

    Tom

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    Quote Originally Posted by john.k View Post
    Doh....how to over react....its just a tent frame,dummies......I say go with 3/16" dia S/S wire for the guys ,and it will be plenty strong enough......you obviously know all about wire fitings,so just go for it.
    I am going with the Amsteel wire rope replacement:

    AMSTEEL-BLUE - Samson Rope

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    Quote Originally Posted by TDegenhart View Post
    Need lengths of beams and cables. Need lengths to point of attachment of the vertical struts to the horizontal member.

    Tom
    This is the rough size of this thing:
    (The weird fractions are all artifacts of just having a couple of key dimensions and can be rounded out..)
    The left guy angle is 28 degrees and the right 36.

    screen-shot-2019-11-09-9.24.57-am.jpg

    I found a retired EE in our friend group to hire on as a consultant- his major CV point was "Well- I just about failed my Loads class" but he works for bottles of beer.
    What's the worse that could happen....

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    TRboatworks,

    Loved the over the top sarcasm. Amazing how many stopped reading at that first paragraph and went instantly to the reply button. I may have had more appreciation than most as I was at one point in my life in the structural concrete business and as such it was immediately obvious how far out there your statement was.

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    Over the weekend I decided to sharpen my statics analysis. First I drew the problem in CAD to get all the relevant data. Next I made some assumptions. Beam sections are rigid bodies and do not deflect. All connections are pin connected. Angles furnished are from the vertical. Loads are uniformly distributed with equal shears at end of unsupported beams (250 lb).truss-2.jpg
    My assumptions are not valid, as the tension in G3 at b is 536#, tension in G3 at c is 451#. Either there will be bending of the beams, the support angles of the poles will change or the lengths of the guys will change.

    At b: Fx=Tg1cos(25)
    Fy=250=Tg1sin(25)
    Tg1=250/sin(25)= 591#
    Fx=~Tg3= 591cos(25)=536#

    At c: Fx=Tg2cos(29)
    Fy=250=Tg2sin(29)
    Tg2=250/sin(29)=515#
    Fx=~Tg3=515cos(29)=451#

    Tom
    Attached Thumbnails Attached Thumbnails truss.jpg  
    Last edited by TDegenhart; 11-11-2019 at 07:20 PM.

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    Tom thank you for taking the time to do that work.


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