Deflection of Structures - Examples

The problems progress from boundary-condition checks to classical beam formulas, moment-area reasoning, conjugate-beam interpretation, virtual work, and Castigliano applications.

Example 1: Boundary Conditions at a Fixed End

A beam is fixed at x=0x=0. State the geometric boundary conditions used in an elastic-curve solution.

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Example 2: Cantilever Tip Deflection under a Point Load

A cantilever of length L=3.0 mL=3.0\text{ m} has E=200 GPaE=200\text{ GPa} and I=60×106 mm4I=60\times10^6\text{ mm}^4. A downward tip load P=20 kNP=20\text{ kN} acts at the free end. Find the tip deflection magnitude.

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Example 3: Cantilever Tip Slope under the Same Point Load

Using the data from Example 2, determine the tip rotation magnitude.

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Example 4: Simply Supported Beam with Midspan Point Load

A simply supported beam has L=6.0 mL=6.0\text{ m}, E=200 GPaE=200\text{ GPa}, I=120×106 mm4I=120\times10^6\text{ mm}^4, and a centered load P=40 kNP=40\text{ kN}. Determine the maximum deflection magnitude.

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Example 5: Moment-Area Change in Slope

Between points AA and BB, the M/EIM/EI diagram is a rectangle of constant ordinate 0.002 rad/m0.002\text{ rad/m} over 4.0 m4.0\text{ m}. Find θB−θA\theta_B-\theta_A.

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Example 6: Tangential Deviation from a Triangular M/EI Diagram

A triangular M/EIM/EI diagram from AA to BB has base 6.0 m6.0\text{ m} and peak ordinate 0.003 rad/m0.003\text{ rad/m} at BB. Find the tangential deviation of BB from the tangent at AA.

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Example 7: Conjugate-Beam Support Transformation

State the conjugate support corresponding to a real cantilever's fixed end and free end.

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Example 8: Virtual Work for a Truss with Two Contributing Members

For a target joint displacement, two truss members have (N,n,L,AE)(N,n,L,AE) values: member 1 (40 kN,0.60,2.0 m,200000 kN)(40\text{ kN},0.60,2.0\text{ m},200000\text{ kN}) and member 2 (−30 kN,−0.40,3.0 m,150000 kN)(-30\text{ kN},-0.40,3.0\text{ m},150000\text{ kN}). Find the displacement contribution sum.

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Example 9: Virtual Work for a Beam with Constant Real and Virtual Moments

Over a 2.0 m2.0\text{ m} segment, let M=30 kN⋅mM=30\text{ kN}\cdot\text{m}, m=0.50 mm=0.50\text{ m} for a unit-load system, and EI=40000 kN⋅m2EI=40000\text{ kN}\cdot\text{m}^2. Find the displacement contribution.

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Example 10: Castigliano from a Simple Strain-Energy Function

The elastic strain energy of a one-degree system is U=P2/(2k)U=P^2/(2k). Use Castigliano's theorem to determine displacement in the direction of PP.

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Example 11: Maxwell-Betti Reciprocity Check

A verified linear-elastic model gives displacement at coordinate AA from a unit load at BB as 2.4 mm2.4\text{ mm}. What displacement should a unit load at AA produce at coordinate BB?

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