MOHR, CHRISTIAN OTTO

(b. Wesselburen, Holstein, 8 October 1835; d. Dresden, Germany, 2 October 1918)

civil engineering.

A descendent of Holstein landowners, Mohr studied engineering at the Polytechnic Institute of Hannover, which he entered in 1851. As an engineer for the state railroads of Hannover and Oldenburg, he not only built some notable bridges but also began to publish original research papers. He published continuously into his eighties. In 1867 Mohr became professor of mechanics and civil engineering at the Technische Hochschule in Stuttgart and, from 1873, at Dresden, where he remained after his retirement in 1900. Commensurate with his steadily growing fame, he received the usual honors in generous measure. Many of his students, including Föppl, described Mohr as their most remarkable teacher. He was of imposing height, proud and taciturn; his ideals in lecturing as well as in writing were simplicity, clarity, and conciseness.

With the exception of one textbook, Mohr published only original research papers. In his first publication (1860), on the theory of continuous beams, he presented the three-moments equation (derived earlier by Clapeyron and Bertot) for the first time in general form by adding terms to account for vertical variations of the supports. In 1868, recognizing that the differential equation of the elastic line has the same form as that of the funicular curve, he developed the method of influence lines, which makes it possible to determine the deflections of a loaded beam, even of varying cross section, without requiring the integration of its differential equation. In 1874 he independently rediscovered a method of determining the stresses in statically indeterminate frameworks that had been published, somewhat obscurely, by Maxwell ten years earlier.“Mohr’s stress circle,” his most widely known contribution, was described in a paper of 1882. Following a suggestion (1866) of Karl Culmann he devised a simple graphic representation of the stresses at one point. Mohr’s theory of failure, based upon the concept of the stress circle, has been widely accepted in engineering practice.

BIBLIOGRAPHY

I. Original Works. Apart from the textbook Technische Mechanik (Stuttgart, 1877), Mohr wrote only research papers, which were collected as Abhandlungen aus dem Gebiete der technischen Mechanik (Berlin, 1906).

II. Secondary Literature. Biographical information on Mohr can be found in three articles by W. Gehler: “Christian Otto Mohr,” in Festschrift Otto Mohr zum 8O. Geburtstag (Berlin, 1916), v-vii;“Otto Mohr,” in Zentralblatt der Bauverwaltung, 38 (1918), 425; and “Otto Mohr,” in Zeitschrift des Vereins deutscher Ingenieure, 62 (1918), 114. See also Poggendorff, V, 868; VI, 1761. Mohr’s technical work is discussed extensively in Stephen P. Timoshenko, History of Strength of Materials (New York, 1953), passim.

Otto Mayr