Shear and Moment in Beams — Worked Examples

Each solution begins with whole-beam equilibrium, then uses a consistent shear and bending-moment sign convention. Diagram ordinates are checked against jumps, slopes, areas, and support conditions.

1. Simply Supported Beam with a Central Point Load

A simply supported beam has span L=6.0 mL=6.0\text{ m} and a downward point load P=20 kNP=20\text{ kN} at midspan. Determine the reactions and maximum bending moment.

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2. Simply Supported Beam with Full-Span UDL

A 5.0 m5.0\text{ m} simply supported beam carries w=8.0 kN/mw=8.0\text{ kN/m} over its full span. Determine the reactions and maximum bending moment.

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3. Cantilever with an End Point Load

A cantilever of length 3.0 m3.0\text{ m} carries a downward free-end load of 12 kN12\text{ kN}. Determine the maximum shear and bending moment magnitudes.

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4. Cantilever with a Full-Span UDL

A 3.0 m3.0\text{ m} cantilever carries w=4.0 kN/mw=4.0\text{ kN/m} over its entire span. Determine the fixed-end shear and moment magnitudes.

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5. Off-Center Point Load on a Simple Beam

A 6.0 m6.0\text{ m} simply supported beam carries 30 kN30\text{ kN} at 2.0 m2.0\text{ m} from the left support. Find the reactions and the maximum moment.

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6. Two Symmetric Point Loads

A 5.0 m5.0\text{ m} simply supported beam carries two 10 kN10\text{ kN} downward loads at x=1.0 mx=1.0\text{ m} and x=4.0 mx=4.0\text{ m}. Determine the reactions and the moment between the loads.

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7. Triangular Distributed Load

A 4.0 m4.0\text{ m} simply supported beam carries a triangular downward load increasing linearly from zero at the left support to 6.0 kN/m6.0\text{ kN/m} at the right support. Determine the reactions and the location of maximum positive moment.

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8. Area under the Shear Diagram

Between two beam stations, shear is constant at +6 kN+6\text{ kN} over a distance of 2.0 m2.0\text{ m}. If the bending moment at the first station is 4 kN⋅m4\text{ kN}\cdot\text{m}, determine the moment at the second.

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9. Singularity Function for a Central Point Load

A 6.0 m6.0\text{ m} simply supported beam carries 20 kN20\text{ kN} at x=3.0 mx=3.0\text{ m}. Write compact shear and moment expressions for 0<x<6 m0<x<6\text{ m} using Macaulay brackets.

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10. Finding a Moment Extremum from Shear

For a simply supported beam with full-span UDL, the shear equation is V(x)=20−8xV(x)=20-8x in kN\text{kN} with xx in meters. Locate the maximum positive bending moment.

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11. Diagram Closure Check

A simply supported beam carries only downward vertical loads totaling 35 kN35\text{ kN}. The computed reactions are RA=18 kNR_A=18\text{ kN} and RB=15 kNR_B=15\text{ kN}. Can the resulting shear diagram close at zero?

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