Math Problem Statement

Find FBD and Reactions

Find FBD and Reactions

Solution

Let's analyze the image and solve for the reactions at the supports.

Step 1: Identify the elements in the diagram.

  • Beam: A simply supported beam with point load and uniformly distributed load (UDL).
  • Supports:
    • Support A: A pinned support (which can take both vertical and horizontal reactions).
    • Support B: A roller support (which can take only vertical reactions).

Step 2: Loadings on the beam.

  • Uniformly Distributed Load (UDL): 30 kN/m, acting from A to C over a span of 3.2 m.
  • Point Load: 24 kN, applied vertically at point B.

Step 3: Free Body Diagram (FBD)

In the FBD, we can represent the loads and reactions as follows:

  • Vertical reaction at A: RAR_A
  • Vertical reaction at B: RBR_B
  • Horizontal reaction at A: HAH_A

We can ignore the horizontal reaction HAH_A, as there are no horizontal forces acting on the system.

Step 4: Equilibrium Equations

We will use the static equilibrium conditions:

  1. Sum of Forces in the Vertical Direction (ΣF_y = 0): RA+RB=Total load on the beamR_A + R_B = \text{Total load on the beam} The total load is the sum of the UDL and the point load.

    UDL load: 30kN/m×3.2m=96kN30 \, \text{kN/m} \times 3.2 \, \text{m} = 96 \, \text{kN}

    Point load: 24kN24 \, \text{kN}

    Therefore, the total vertical load is: RA+RB=96+24=120kNR_A + R_B = 96 + 24 = 120 \, \text{kN} So, RA+RB=120kNR_A + R_B = 120 \, \text{kN}

  2. Sum of Moments about Point A (ΣM_A = 0): The moment created by each force around point A must sum to zero.

    Moment due to UDL: The UDL creates a resultant force of 96 kN acting at the center of its distribution (i.e., 1.6 m from A). Thus, the moment is: Moment of UDL=96kN×1.6m=153.6kN\cdotpm\text{Moment of UDL} = 96 \, \text{kN} \times 1.6 \, \text{m} = 153.6 \, \text{kN·m}

    Moment due to point load at B: The point load of 24 kN acts at a distance of 4.0 m from A. The moment is: Moment of point load=24kN×4.0m=96kN\cdotpm\text{Moment of point load} = 24 \, \text{kN} \times 4.0 \, \text{m} = 96 \, \text{kN·m}

    Moment due to reaction at B: RBR_B creates a clockwise moment about A, and its distance from A is 4.0 m: Moment of RB=RB×4.0m\text{Moment of } R_B = R_B \times 4.0 \, \text{m}

    Using ΣMA=0ΣM_A = 0: RB×4.0=153.6+96R_B \times 4.0 = 153.6 + 96 RB×4.0=249.6R_B \times 4.0 = 249.6 RB=249.64.0=62.4kNR_B = \frac{249.6}{4.0} = 62.4 \, \text{kN}

  3. Sum of Forces in the Vertical Direction (Revisited): Now that we have RBR_B, we can solve for RAR_A: RA+62.4=120R_A + 62.4 = 120 RA=12062.4=57.6kNR_A = 120 - 62.4 = 57.6 \, \text{kN}

Step 5: Final Reactions

  • Reaction at A (RAR_A) = 57.6 kN (upward)
  • Reaction at B (RBR_B) = 62.4 kN (upward)

Step 6: Free Body Diagram (FBD)

  • UDL of 30 kN/m over 3.2 m acting from A to C.
  • Point load of 24 kN acting at B.
  • Reaction forces RA=57.6kNR_A = 57.6 \, \text{kN} and RB=62.4kNR_B = 62.4 \, \text{kN}.

Would you like the detailed drawing of the FBD?


Here are 5 related questions to expand on this topic:

  1. How would the reaction forces change if the UDL was increased to 40 kN/m?
  2. What would be the reactions if the point load was moved 0.5 m to the left?
  3. How does the distance between the supports affect the reaction forces?
  4. Can you calculate the bending moment at the midpoint between A and B?
  5. What would happen if the roller support at B was replaced with a pinned support?

Tip: Always double-check your moment calculations by verifying the dimensions and force magnitudes, especially when dealing with distributed loads.

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Math Problem Analysis

Mathematical Concepts

Statics
Equilibrium
Beam Reactions

Formulas

ΣF_y = 0: R_A + R_B = Total Load
ΣM_A = 0: Sum of Moments about A
Moment of UDL = UDL * distance to center
Moment of Point Load = Point Load * distance

Theorems

Equilibrium of Forces and Moments

Suitable Grade Level

Undergraduate Engineering