The purpose of structural idealisation is to
Answer: A
Idealisation trades a small, understood loss of accuracy for a very large gain in tractability. The art lies in choosing simplifications that preserve the behaviour being investigated while discarding detail that does not affect it.
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In the standard idealisation of a stiffened panel, the direct stress is assumed to be carried by
Answer: B
Lumping the direct-stress-carrying material into discrete areas reduces integration to summation. The skin is left to carry shear only, which reflects where the material and the stiffness genuinely are in a stiffened structure.
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The area assigned to a boom from an adjacent skin panel depends on
Answer: C
The standard formula shares the panel's area between its two ends so the idealised section carries the same direct load as the real one. Where the stress at the two ends is equal the split is even; where it reverses, the share falls sharply.
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When the stress at one end of a panel is equal and opposite to that at the other, the boom area contribution is
Answer: D
Substituting a stress ratio of minus one into the boom formula leaves a factor of one, giving one sixth of the panel area to each end. Compare the uniform-stress case, where the factor is three and each end receives a half.
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Effective width, as applied to a buckled compression panel, means
Answer: A
After buckling the middle of a panel sheds load while material close to the stiffener continues to carry it. Counting only that effective strip keeps the section properties honest and is the standard treatment in a compression-critical structure.
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The effective width of a buckled panel decreases as
Answer: B
The von Karman expression makes the effective width vary inversely with the square root of the stress, so a more heavily loaded stiffener carries a narrower strip of working skin. The structure therefore becomes progressively less efficient as it approaches its ultimate load.
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A structure is described as effectively rigid in an idealisation when
Answer: C
Treating a very stiff component as rigid removes degrees of freedom without materially changing the answer, and it simplifies both hand analysis and finite element models. The judgement is relative: rigid against what, and for which quantity of interest.
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The chief risk of an over-simplified idealisation is that it
Answer: D
Removing a member or a connection that genuinely carries load redistributes the predicted stresses away from reality, and the error can be unconservative. Every simplification should be justified by asking what load path it removes and whether that matters.
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Increasing the number of booms used to idealise a section generally
Answer: A
More booms follow the real distribution of material more closely, and the idealised results converge towards the exact ones. The trade against effort is the same one that governs mesh density in a finite element model.
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In finite element idealisation, a rod or bar element carries
Answer: B
Correct answer: Axial load only
A rod or bar element has stiffness along its own axis and none in bending or torsion, so it carries tension and compression alone. That is exactly what makes it the finite element counterpart of an idealised boom, which is defined as carrying direct stress only while the panels between the booms carry the shear. A beam element is the one that carries bending as well.
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