“When a structure fails or seems in danger of failing the natural instinct of the engineer may be to specify the use of a ‘stronger’ material: in the case of steel, what is known as a ‘higher tensile’ steel. With large structures this is generally a mistake, for it is clear that most of the strength, even of mild steel, is not really being used. This is because, as we have seen, the failure of a structure may be controlled, not by the strength, but by the brittleness of the material. [...] the toughness of most metals is undoubtedly reduced very greatly as the tensile strength increases.”