All questions of Deflection of Beams for Civil Engineering (CE) Exam

For the beam shown in the figure, the elastic curve between the supports B and C will be
  • a)
    Circular
  • b)
    Parabolic
  • c)
    Elliptic
  • d)
    A straight line
Correct answer is option 'A'. Can you explain this answer?

Neha Joshi answered
BMD for the loading will be
Between B and C, BMD is a straight line BM = Constant
Now,
⇒ R = Constant Means curve of constant radius.
Hence, circular.

A beam of span 6m and of uniform flexural rigidity EI = 40000 kNm2 is subjected to a clockwise couple of 300 kNm at a distance of 4m from the left end. The deflection at the point of application of the couple is _______ mm
(A) 9.12
(B) 9.72
    Correct answer is option ''. Can you explain this answer?

    Geetika Shah answered
    Taking moments about A, Vb × 6 = 300
    Vb = 50 kN ↑
    ∴ Va = 50 kN ↓
    The B.M at any section distant x from A is given by,
    Integrating,
    Integrating !gain,
    EIy =
    AT x = 0, t = 0
    ∴ C2 = 0
    At x = 6, y = 0
    ∴ 0 =
    ∴ C1 = 200
    Deflection at C. Putting x = 4m, in the deflection equation,
    EIyc =
    = 266.67
    Max. deflection. This will occur in the larger segment. Equating the slope to zero, we get,
    ∴ x = 2√2 m
    Putting x = 2√2 m in the deflection equation
    EIymax =
    ymax =
    = 9.43 mm
    Question_Type: 5

    The maximum deflection of a cantilever of 10.0 m span, an EI = 200.0MN/m2 subjected to a distributed load of 8.0 kN/m is
    • a)
      20 mm
    • b)
      50 mm
    • c)
      225 mm
    • d)
      500 mm
    Correct answer is option 'B'. Can you explain this answer?

    Aarav Chauhan answered
    Maximum Deflection of Cantilever Beam

    Given parameters:
    - Span (L) = 10.0 m
    - EI = 200.0 MN/m2
    - Distributed load (w) = 8.0 kN/m

    To determine the maximum deflection of the cantilever beam, we need to follow the steps below:

    1. Calculate the reaction force (R) at the fixed end of the beam using the formula:
    R = wL

    Substituting the given values, we get:
    R = 8.0 kN/m x 10.0 m = 80.0 kN

    2. Determine the maximum deflection (δmax) using the formula:
    δmax = (5wL^4)/(384EI)

    Substituting the given values and the calculated reaction force, we get:
    δmax = (5 x 8.0 kN/m x (10.0 m)^4)/(384 x 200.0 MN/m2 x 80.0 kN)
    δmax = 0.050 m or 50 mm (approximately)

    Therefore, the correct answer is option B, which is 50 mm.

    A cantilever 3m long, and of symmetrical section 250 mm deep carries a uniformly distributed load of 30 kN/m run throughout together with a point of 80 kN at a section 1.2 m from fixed end. The deflection at the free end is __________ mm (Take E = 200 GPa, I = 54000 cm4)
    (A) 3.9
    (B) 4.5
      Correct answer is option ''. Can you explain this answer?

      AB fixed at end B, Free at end A carrying a point load W at L1 from B end UDL of W throughout to length EI = flexural rigidity δ = deflection at free end
      =
      where, L1 = 1.2m, L2 = 1.8m, L = 3m,
      W = 80 kN and W = 30 kN/m
      EI = 200 × 106 kN/m2 × 54000 × 10−8 m4
      = 108000 kNm2
      δ =
      = 0.42666 × 10−3 + 0.96 × 10−3 + 2.8125 × 10−3
      = 4.2 × 10−3m = 4.2 mm
      Question_Type: 5

      A prismatic beam of length L is simply supported at its ends and subjected to a total UDL of W spread over its entire span. It is then propped at its Centre to neutralize the deflection. The net B.M. at its Centre will be
      • a)
        WL
      • b)
        WL/3
      • c)
        WL/24
      • d)
        WL/32
      Correct answer is option 'D'. Can you explain this answer?

      Anita Menon answered
      The propped reaction neutralize Downward deflection due to udl = upward Deflection due to support at C
      ∴ moment at C Mc =
      RA + RB + RC = W
      ∴ Rc =
      RA + RB = W -
      Due to symmetry RA = RB =
      ∴ Mc =
      =
      =
      = (Clockwise)

      A horizontal beam (I = 8.616 × 107mm4) carries a uniformly distributed load of 50 kN over its length of 3m. The beam is supported by three vertical steel tie rods, each 1.80m long. One at each end and one at in the middle, the end rods having a diameter of 25mm and the centre rod a diameter of 30mm. The deflection of the centre of the beam is _________mm (Take E = 2 × 105 N/mm2)
      (Take E = 2 × 105 N/mm2)
      (A) 0.131
      (B) 0.139
        Correct answer is option ''. Can you explain this answer?

        Area of each rod
        = A1 = = 490.87 mm2
        Area of the middle rod
        = A2 = = 706.86 mm2
        Let, P1 = Tension in each end rod
        P2 = Tension in the middle rod
        f1 = Stress in the rods
        f2 = Stress in the middle rod
        δ1 = Extension of each end rod
        δ2 = Extension of the middle rod
        Deflection of the midpoint of the beam
        δ2 − δ1 =
        EI(δ2 − δ1) =
        Deflection of beams
        8.616 × 107 × 1800(f2 − f1)
        =
        2205.696(f2 − f1) = 250 − 5654.88f2
        2205.696f2 − 2205.696f1 = 250 − 5654.88f2
        7860.576f2 − 2205.696f1 = 250 ⋯ ①
        2f1A1 + f2A2 = 50
        2f1(490.87) + f2 (706.86) = 50
        981.74f, + 706.86f, = 50 ⋯ ②
        From equation ① and ②,
        7860.576f2 − 2205.696f1 = 5(981.74f,1 + 706.86f2)
        7860.576f2 − 2205.696f1 = 4908.70f1 + 3534.3f2
        4326.76f2 = 7114.396f1
        ∴ f2 = 1.644f1
        Substituting in equation ②
        981.74f1 + 706.86 × 1.644f1 = 50
        2143.8178f1 = 50
        f1 = 0.02332 kN/mm2 = 23.32 N/mm2
        f2 = 1.644 × 23.32 = 38.33 N/mm2
        Deflection of the midpoint of the beam
        δ2 − δ1 =
        =
        =0.135 mm
        Question_Type: 5

        If the actual beam has both ends fixed, then the ends of the conjugate beam will be
        • a)
          Fixed at both ends
        • b)
          Free at both ends
        • c)
          Fixed at one end, free at other end
        • d)
          Hinged at one end, free at other end
        Correct answer is option 'B'. Can you explain this answer?

        Explanation:

        When a beam is fixed at both ends, it means that the beam is restrained from both translation and rotation at those points. In other words, the supports at the ends provide both vertical and horizontal reactions, as well as moments to resist any applied loads.

        The conjugate beam is a mathematical tool used in structural analysis to determine the deflection and slope of a beam. It is derived from the original beam by following a set of rules:

        1. The length of the conjugate beam is the same as the original beam.
        2. The supports of the conjugate beam are located at the same positions as the original beam.
        3. The reactions at the supports of the conjugate beam are equal to the slopes of the original beam at those points.
        4. The loads on the conjugate beam are equal to the bending moments of the original beam divided by the length of the beam.

        In this case, the actual beam has both ends fixed:

        When a beam has both ends fixed, it means that the ends are restrained from translation and rotation. The supports at the ends provide both vertical and horizontal reactions, as well as moments to resist any applied loads.

        Conjugate beam for a beam with both ends fixed:

        When we apply the rules of the conjugate beam, we find that the ends of the conjugate beam will be free at both ends. This means that the supports of the conjugate beam will not provide any reactions or moments. The conjugate beam will be free to translate and rotate at both ends.

        Reasoning:

        The fixed support at the ends of the actual beam provides both vertical and horizontal reactions, as well as moments to resist any applied loads. However, when we convert the actual beam to its conjugate beam, the supports of the conjugate beam do not provide any reactions or moments. This is because the conjugate beam is a mathematical tool used to determine the deflection and slope of the original beam, and it does not represent the actual physical supports of the beam.

        Therefore, the ends of the conjugate beam will be free at both ends (option B).

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