Example 1

Calculate the reactions in a statically indeterminate beam using the Clebsch method.

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Solution

Indeterminate systems are solved using the Clebsch Method in a similar way to displacements in determinate systems, with the difference being that there is one additional equation (boundary condition) and one additional unknown (reaction).

Clebsch Method

Equilibrium equations

𝑋=0𝑅2=0𝑌=0𝑅1+𝑅35𝑞𝑙=0𝑅1=5𝑞𝑙𝑅3𝑀1=0𝑀𝑈𝑅33𝑙+252𝑞𝑙2=0𝑀𝑈=3𝑙𝑅3252𝑞𝑙2

Classical Clebsch Method

𝑀𝑔=𝑀𝑢𝑥0+𝑅1𝑥12𝑞𝑥2+𝑅3(𝑥3𝑙)𝑀𝑔=3𝑅3𝑙𝑥0252𝑞𝑙2𝑥0+5𝑞𝑙𝑥𝑅3𝑥12𝑞𝑥2+𝑅3(𝑥3𝑙)𝐸𝐼𝑤=𝑀𝑔𝐸𝐼𝑤=3𝑅3𝑙𝑥0+252𝑞𝑙2𝑥05𝑞𝑙𝑥+𝑅3𝑥+12𝑞𝑥2𝑅3(𝑥3𝑙)𝐸𝐼𝑤=3𝑅3𝑙𝑥+252𝑞𝑙2𝑥5𝑞𝑙𝑥22+𝑅3𝑥22+12𝑞𝑥33𝑅3(𝑥3𝑙)22+𝐶𝐸𝐼𝑤=3𝑅3𝑙𝑥22+252𝑞𝑙2𝑥225𝑞𝑙𝑥36+𝑅3𝑥36+12𝑞𝑥412𝑅3(𝑥3𝑙)36+𝐶𝑥+𝐷

Boundary conditions

𝑤(0)=0𝐶=0𝑤(0)=0𝐷=0𝑤(3𝑙)=03𝑅3𝑙322𝑙2+252𝑞𝑙232𝑙225𝑞𝑙33𝑙36+𝑅333𝑙33+12𝑞34𝑙412=09𝑅3𝑙3+2978𝑞𝑙4=0

Reactions

𝑅3=338𝑞𝑙𝑅1=78𝑞𝑙𝑀𝑈=18𝑞𝑙2