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Homework Help: Column Reactions

  1. Sep 9, 2008 #1
    A column AB is anchored to the ground by a pin-joint at A, and is held in a vertical position by various loads as shown. Determine:
    (i) Magnitude of force f1
    (ii) Magnitude and direction of the reaction at A

    I know how to calculate F1 if it was on a horizontal or vertical. But I'm not sure How to calculate it with the 5kN force offset by 0.5 m horizontally. We haven't been taught how to calculate with anything like this yet.

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  2. jcsd
  3. Sep 9, 2008 #2


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    At the pin support A, there are 2 unknown force components, Ax in the horizontal direction and Ay in the vertical direction. I am sure you are familiar with the three equations of equilibrium,
    sum of forces in x direction = 0
    sum of forces in y direction, and
    sum of moments about any point =0.
    You should first resolve all applied forces, known or unknown, into their x and y components, Fcos theta and Fsin theta, respectively, each applied at the known points. Then sum moments about support A = 0 , paying attention to clockwise vs. counterclockwise moments. Note that the 5kN offset force also produces a moment about A. The moment of a force about a point (axis) is the product of the force times the perpendicular distance from the line of action of the force to that point.
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