It was with the estimation of arch thrust that the first numerical calculations were concerned, as well as with the attempt to understand arch behaviour in general. As will be seen, recognisably modern work had been done before 1717, but it was in that year that Gautier's book on bridge abutments was published; he summarised the five difficulties that needed resolution:
The thickness of abutment piers.
The dimensions of internal piers as a proportion of the span of the arches.
The thickness of the arch ring.
The shape of the arches.
The dimensions of retaining walls to hold back soil.
Gautier's first problem requires for its resolution a knowledge of the value of the abutment thrust from the arch, and his problems 3 and 4 recognise that the solution depends both on the shape and the thickness of the arch. Problem 5 widens the enquiry to a field of civil engineering which is now treated by the sciences of geotechnical engineering and soil mechanics.
Robert Hooke, in 1675, addressed the structural problems of the arch. He published in that year a Latin anagram concerning the true form of all manner of arches for building, with the true butment necessary to each of them . The anagram gives Ut pendet continuum flexile, sic stabit contiguum rigidum inversum as hangs the flexible line, so but inverted will stand the rigid arch . Publication in anagram form was common in the seventeenth century. The scientific climate was competitive, and scientists...
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