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6 July, 02:12

Two concrete spans of a 250-m-long bridge are placed end to end so that no room is allowed for expansion. If a temperature increase of 20.0C occurs, what is the height y to which the spans rise when they buckle?

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  1. 6 July, 03:17
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    y = 2.74 m

    Explanation:

    The linear thermal expansion processes are described by the expression

    ΔL = α L ΔT

    Where α the thermal dilation constant for concrete is 12 10⁻⁶ºC⁻¹, ΔL is the length variation and ΔT the temperature variation in this case 20ªc

    If the bridge is 250 m long and is covered by two sections each of them must be L = 125 m, let's calculate the variation in length

    ΔL = 12 10⁻⁶ 125 20

    ΔL = 3.0 10⁻² m

    Let's use trigonometry to find the height

    The hypotenuse Lf = 125 + 0.03 = 125.03 m

    Adjacent leg L₀ = 125 m

    cos θ = L₀ / Lf

    θ = cos⁻¹ (L₀ / Lf)

    θ = cos⁻¹ (125 / 125.03)

    θ = 1,255º

    We calculate the height

    tan 1,255 = y / x

    y = x tan 1,255

    y = 125 tan 1,255

    y = 2.74 m
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