Beam Deflections: Solved Problems

A comprehensive collection of worked examples demonstrating beam deflection calculations using various methods, including Double Integration, Area-Moment, Conjugate Beam, and Superposition.

Important Sign Convention

In the following examples, downward deflection is generally considered negative, and upward deflection is positive. Sagging moments (causing tension at the bottom) are considered positive, while hogging moments are negative.

1. Deflection of a Cantilever Beam with a Concentrated Load (Double Integration)

Problem: A cantilever beam of length LL carries a concentrated load PP at the free end. Determine the maximum deflection and slope using the Double Integration Method.

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2. Deflection of a Cantilever Beam with a Uniformly Distributed Load

Problem: A cantilever beam of length LL carries a uniformly distributed load ww over its entire length. Determine the maximum deflection using the Double Integration Method.

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3. Deflection of a Simply Supported Beam with a Uniform Load

Problem: A simply supported beam of length LL carries a uniform load ww over its entire length. Determine the maximum deflection.

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4. Deflection of a Simply Supported Beam with a Point Load at Midspan

Problem: A simply supported beam of length LL carries a concentrated load PP at its center (x=L2x = \frac{L}{2}). Determine the maximum deflection using Double Integration.

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5. Area-Moment Method: Cantilever Beam with Point Load

Problem: A cantilever beam of length L=4.00 mL = 4.00 \text{ m} is subjected to a point load P=15.0 kNP = 15.0 \text{ kN} at the free end. The flexural rigidity is EI=1.20×104 kNm2EI = 1.20 \times 10^4 \text{ kN}\cdot\text{m}^2. Find the deflection at the free end using the Area-Moment Method.

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6. Conjugate Beam Method: Simply Supported Beam Slope

Problem: A simply supported beam AB of length L=6.00 mL = 6.00 \text{ m} has a concentrated load P=24.0 kNP = 24.0 \text{ kN} at midspan. EIEI is constant. Find the slope at support A (θA\theta_A) using the Conjugate Beam Method.

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7. Method of Superposition: Cantilever Beam with Uniform and Point Load

Problem: A cantilever beam of length L=5.00 mL = 5.00 \text{ m} is subjected to a uniform load w=10.0 kN/mw = 10.0 \text{ kN/m} over its entire length, and a concentrated point load P=20.0 kNP = 20.0 \text{ kN} at the free end. The beam has a constant flexural rigidity EI=1.00×104 kNm2EI = 1.00 \times 10^4 \text{ kN}\cdot\text{m}^2. Determine the maximum deflection at the free end.

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8. Method of Superposition: Simply Supported Beam with Two Point Loads

Problem: A simply supported beam of length L=8.00 mL = 8.00 \text{ m} carries a load P1=30.0 kNP_1 = 30.0 \text{ kN} at a=2.00 ma = 2.00 \text{ m} from the left support, and P2=40.0 kNP_2 = 40.0 \text{ kN} at midspan (4.00 m4.00 \text{ m}). Given EI=2.00×104 kNm2EI = 2.00 \times 10^4 \text{ kN}\cdot\text{m}^2, find the deflection at midspan using superposition.

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9. Conceptual Case Study: Stiffness vs. Strength

Problem: An engineer needs to design a floor beam for an office building. The beam satisfies all bending moment and shear force requirements (strength), but its calculated deflection under service loads exceeds the allowable limit of L/360L/360. What are the most effective ways to solve this issue without changing the material?

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10. Conceptual Case Study: Camber in Steel Beams

Problem: A long-span steel beam is designed to support a heavy concrete floor slab. Under the dead load of the wet concrete, the beam is expected to deflect significantly. How can this be addressed during fabrication to ensure a level floor?

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11. Conceptual Case Study: Support Settlement

Problem: A continuous beam rests on three supports. Over time, the middle support settles downwards by a few millimeters due to soil consolidation. How does this affect the deflection and internal forces of the beam?

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12. Conceptual Case Study: The Effect of Support Types on Deflection

Problem: Compare the maximum deflection of a simply supported beam and a fixed-ended beam, both subjected to the same uniformly distributed load ww and having the same span LL and rigidity EIEI.

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