August Föppl

August Föppl started his civil engineering studies in 1869 at Darmstadt TH and continued them at Stuttgart TH, where the excellent lectures of Otto Mohr developed his interest in mechanics and strength of materials. After Mohr’s departure from Stuttgart in 1874, Föppl switched universities again and completed his civil engineering studies at Karlsruhe TH in 1874. He admitted not understanding the lectures of Franz Grashof in Karlsruhe; it was not until many years later that he referred to Grashof when carrying out his own research [Föppl, A. & Föppl, O., 1925, pp. 84–85]. Following his studies he worked for a short time in the Baden Highways Department, just enough to satisfy military service obligations, and then in the autumn of 1876 took up a temporary teaching post at the Building Trades School in Holzminden. From 1877 to 1894 he taught at the Municipal Industrial School in Leipzig. This period was his most fruitful in terms of contributions to the theory of structures. For example, he wrote four sections for the appendix of the 1878 German 2nd edition of Navier’s Mechanik der Baukunst[Navier,1878]:Anwendungen der Elasticitätsgesetze auf die Berechnung der Baukonstruktionen (pp. 506–522), Theorie des Fachwerks (pp. 523–556), Die Theorie der Tonnengewölbe (pp. 557–581) and Dimensions- Berechnung der Eisen- und Stahl-Constructionen (pp. 582–589). Of these four contributions, the second, Theorie des Fachwerks, is particularly noteworthy for its clear definitions, and appeared in expanded form as a book in 1880. This was followed one year later by the Theorie der Gewölbe, likewise much expanded. He combined both monographs under the title Mathematische Theorie der Baukonstruktionen, which in 1886 was acknowledged by the University of Leipzig 1886 as a dissertation. Föppl was the first to present a self-contained theory of space frames (1892). These books constitute a significant contribution to the consummation of theory of structures. In that same year he was appointed regular associate professor for cultivation and mechanical engineering in agriculture at the University of Leipzig. His studies in electrical engineering under Gustav Wiedemann (1826–99) at the University’s Physics Institute were crowned in 1894 with his monograph Einführung in die Maxwellsche Theorie der Elektricität; it was here that he revealed for the first time the theoretical and practical strengths of vector analysis, which Föppl qualified as “the mathematical sign language of the physics of the future” [Hiersemann, 1990, p. 60]. In 1894 he succeeded Johann Bauschinger (1834–94) in the chair of applied mechanics and as head of the Mechanical-Technical Laboratory at Munich TH. He regarded the aim of materials testing more as “establishing the behaviour of complete construction parts, assembled constructions too, rather than the materials used themselves” [Prinz, 1924, p. 1]. This meant he was the first to establish a new understanding of materials testing, which later would become a successful reference model for engineering science experimentation. It was during his period in Munich that Föppl wrote what was the most influential textbook of applied mechanics in Germany up to that time: Vorlesungen über Technische Mechanik (1898–1910) – six volumes which appeared in numerous editions and were translated into several languages; more than 100 000 copies had been sold by 1925. His prolific output was complemented in 1920 by the two-volume work Drang und Zwang written in conjunction with his son Ludwig. In 1917 he succeeded in expanding the St. Venant torsion theory, work which his student Constantin Weber continued later. Föppl’s most important student was Ludwig Prandtl, who in 1899 gained his doctorate under Föppl with a dissertation on lateral buckling phenomena of beams with slender rectangular cross-sections. A history of the teaching of applied mechanics in the Germanspeaking countries would have to analyse the textbooks of Franz Joseph Ritter von Gerstner, Julius Weisbach, August Föppl and István Szabó. But one Thing is certain: only August Föppl's books on mechanics became best-sellers. He thus created the most influential school of applied mechanics and was the first engineer to be accepted as a full member of the Bavarian Academy of Sciences. Both Munich TH and Darmstadt TH awarded him honorary doctorates.

Main contributions to structural analysis:

Theorie des Fachwerks [1880]; Theorie der Gewölbe [1881]; Das Fachwerk im Raum [1892]; Vorlesungen über Technische Mechanik [1898–1910]; Über den elastischen Verdrehungswinkel eines Stabes [1917]; Drang und Zwang [1920]