riff_raff wrote:(...) I would disagree. Automotive steel frames and unibody structures only have holes where absolutely necessary. (...)
holes do not have to be circular. the simplest frame is made from beams and between them you have an empty space - holes. bridges i.e. are made this way as well as the roll cages.
wheel rims are good example - if you look at them they are not made as a solid. you have hub, rim, the spokes connecting them and holes between them. at the end you are getting structure which is strong, light and has provide enough cooling capability.
round bars, or tubes, subjected to bending and/or torsion are another good example. you can remove material from the inside, as it does not do much, and still have strong, stiff and light design. roll cages are made from tubes empty inside, not beams.
in some bolted joint in pressure vessels (i.e. casings of gas turbines subjected to high thermal gradients in radial direction) you are using holes with radial saw-cuts in the flanges to "break" the hoop stress. the holes themselves in fact creates local stress concentration, but as they are placed in low stress regions it's not a big issue. more important is you are lowering stress in the flange.
problem with the Comet was not caused by the presence of the holes but more due their shape and reinforcements around them. they were almost square with very small radii in the corners which lead to high stress concentration and subsequently to fatigue damage. we still have windows in the planes but their shape and design have changes since then. it was possible thanks to the tragedies like the one you've mentioned.
holes, like most design features, can be made to work in our favor or can make a lot of mess. it's all down to knowledge and experience of the designer.
regards,
stan
