Shear force bending moment

Physics

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To determine the shear force and bending moment along the beam, we will use the previously calculated reactions:

  • Reaction at A (RAR_A) = 5 units (upward)
  • Reaction at B (RBR_B) = 5 units (upward)
  • Point load (PP) = 10 units (downward) at x=3x=3 from A.
  • Total beam length = 6 units.

We will analyze the beam in two sections:

  1. From A to the point load (0 < x < 3)
  2. From the point load to B (3 < x < 6)

Shear Force Calculation

Shear force (V(x)V(x)) is the algebraic sum of the vertical forces to the left of the section. Upward forces are positive, downward forces are negative.

  1. Shear force for the section 0≤x<30 \le x < 3 (from A to the point load).

    Considering a section at a distance xx from A:

    V(x)=RAV(x) = R_A V(x)=5V(x) = 5

    The shear force is constant in this section.

  2. Shear force for the section 3<x≤63 < x \le 6 (from the point load to B).

    Considering a section at a distance xx from A:

    V(x)=RA−PV(x) = R_A - P V(x)=5−10V(x) = 5 - 10 V(x)=−5V(x) = -5

    The shear force is constant in this section.

    Bending Moment Calculation

    Bending moment (M(x)M(x)) is the algebraic sum of the moments of all forces to the left of the section about that section. Counter-clockwise moments are positive, clockwise moments are negative.

  3. Bending moment for the section 0≤x<30 \le x < 3 (from A to the point load).

    Considering a section at a distance xx from A:

    M(x)=RA×xM(x) = R_A \times x M(x)=5xM(x) = 5x

    At x=0x=0 (support A), M(0)=5×0=0M(0) = 5 \times 0 = 0.
    At x=3x=3 (at the point load), M(3)=5×3=15M(3) = 5 \times 3 = 15.

  4. Bending moment for the section 3<x≤63 < x \le 6 (from the point load to B).

    Considering a section at a distance xx from A:

    M(x)=RA×x−P×(x−3)M(x) = R_A \times x - P \times (x - 3) M(x)=5x−10(x−3)M(x) = 5x - 10(x - 3) M(x)=5x−10x+30M(x) = 5x - 10x + 30 M(x)=−5x+30M(x) = -5x + 30

    At x=3x=3 (at the point load), M(3)=−5×3+30=−15+30=15M(3) = -5 \times 3 + 30 = -15 + 30 = 15.
    At x=6x=6 (support B), M(6)=−5×6+30=−30+30=0M(6) = -5 \times 6 + 30 = -30 + 30 = 0.

    Summary of Shear Force and Bending Moment Functions

    The shear force and bending moment functions for the beam are:

    Shear Force (V(x)V(x)):

    V(x)={5for 0≤x<3−5for 3<x≤6V(x) = \begin{cases} 5 & \text{for } 0 \le x < 3 \\ -5 & \text{for } 3 < x \le 6 \end{cases}

    Bending Moment (M(x)M(x)):

    M(x)={5xfor 0≤x<3−5x+30for 3<x≤6M(x) = \begin{cases} 5x & \text{for } 0 \le x < 3 \\ -5x + 30 & \text{for } 3 < x \le 6 \end{cases}

    The maximum bending moment occurs at the point load (x=3x=3), with a value of 15 units.

    The final answer is Shear Force: V(x)={5for 0≤x<3−5for 3<x≤6,Bending Moment: M(x)={5xfor 0≤x<3−5x+30for 3<x≤6\boxed{\text{Shear Force: } V(x) = \begin{cases} 5 & \text{for } 0 \le x < 3 \\ -5 & \text{for } 3 < x \le 6 \end{cases}, \text{Bending Moment: } M(x) = \begin{cases} 5x & \text{for } 0 \le x < 3 \\ -5x + 30 & \text{for } 3 < x \le 6 \end{cases}}.

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