Structural Idealisation Questions and Answers

Answer: A

Correct answer: -2

Setting the bracket to zero,

which would require the far end of the panel to carry twice the stress of the near end and of opposite sign. The formula is empirical and is not intended to be used at such a ratio; the question is really a check that the algebra, and the range over which the expression is meaningful, are both understood.

Answer: B

Both are true and the second explains the first. The idealisation reflects where the material actually is, and the skin's own direct-stress contribution is credited by lumping part of its area into the adjacent booms rather than being discarded.

Answer: C

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the mechanism. Once a panel buckles, its middle can carry no more load and sheds it, while the material along the stiffener is restrained from buckling and continues to take stress. Only that strip is credited, and the panel is treated as a narrow band of fully effective skin either side of the stiffener with nothing in between.

Answer: D

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason explains the loss of efficiency. Since \( 2w \propto 1/\sqrt{\sigma} \), raising the stiffener stress narrows the working strip of skin, so a larger share of the load must be carried by the stiffener alone. Each further increment of load is therefore taken by less material than the one before, and the structure becomes progressively less efficient as it approaches ultimate.

Answer: A

Both statements are true and the second is the reason for the first. Applying symmetry boundary conditions to an asymmetric case imposes a constraint the real structure does not have, and the answer is simply wrong rather than merely approximate.

Answer: B

Both are true and the second explains the first. Refining the mesh merely produces a larger number, so the honest responses are to model the fillet the real part has, or to assess the region by fracture mechanics instead.

Answer: C

Both statements are true and the second is the reason for the first. It is the cheapest check available and catches misapplied loads, unit errors and unintended restraints, all of which are common and none of which the solver will report.

Answer: D

The assertion is false and the reason is true. Rigid connections stiffen the model and misdistribute the load between parts, sometimes unconservatively. Calibrated spring elements reproduce the real joint flexibility at very little cost.

Answer: A

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason states what a convergence study is for. A single run gives a number with no indication of how far it stands from the exact solution of the equations being solved. Refining the mesh and watching the quantity of interest settle is the only evidence available that the discretisation error is small - and it must be the quantity of interest, since displacements converge long before peak stresses.

Answer: B

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason is the principle itself. Saint-Venant holds that two statically equivalent load systems produce the same stress field at distances large compared with the region over which they are applied. A bolt pattern may therefore be replaced by its resultant for anything beyond a bolt spacing or two - but not for the local bearing and net section stresses at the bolts themselves, which is exactly where the principle does not apply.