What formulas are used in bridges?
This question is asked most often in connection with suspension bridges and arches. Semicircles, parabolas and catenaries are the curves usually mentioned. While it is true that arches have use arcs of circles for hundreds of years, this has been done to simplify the construction, particularly of expensive centring, rather than from any theoretical considerations. Formulas do exist in engineering, often giving the results for such calculations as deflection of a beam of given cross section with a given distribution of loading, distribution of stresses within a member, and so on. But the overall shape and size of a bridge and its parts are more likely to emerge from long series of calculations which are intended to optimize a large number of variables, one of which may be the cost. That is not to say that an individual engineer may not have preferences in terms of type of bridge, and shapes to be used. But the idea of a formula guiding the design is generally wide of the mark. Engineeri
