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Christian Otto Mohr (8 October 1835 – 2 October 1918) was a German
civil engineer A civil engineer is a person who practices civil engineering – the application of planning, designing, constructing, maintaining, and operating infrastructure while protecting the public and environmental health, as well as improving existing ...
. He is renowned for his contributions to the field of
structural engineering Structural engineering is a sub-discipline of civil engineering in which structural engineers are trained to design the 'bones and muscles' that create the form and shape of man-made structures. Structural engineers also must understand and cal ...
, such as
Mohr's circle Mohr's circle is a two-dimensional graphical representation of the transformation law for the Cauchy stress tensor. Mohr's circle is often used in calculations relating to mechanical engineering for materials' strength, geotechnical engine ...
, and for his study of stress.


Biography

He was born on 8 October 1835 to a landowning family in
Wesselburen Wesselburen () is a small town in the district of Dithmarschen in the German Federal State of Schleswig-Holstein. It is situated near the North Sea coast, approximately west of Heide. Wesselburen is part of the '' Amt'' ("collective municipalit ...
in the
Holstein Holstein (; nds, label=Northern Low Saxon, Holsteen; da, Holsten; Latin and historical en, Holsatia, italic=yes) is the region between the rivers Elbe and Eider. It is the southern half of Schleswig-Holstein, the northernmost state of Germa ...
region. At the age of 16 attended the
Polytechnic School Polytechnic School, often referred to simply as Poly, is a college preparatory private day school located in Pasadena, California with approximately 850 students enrolled in grades Kindergarten through 12. The school is a former member of th ...
in
Hannover Hanover (; german: Hannover ; nds, Hannober) is the capital and largest city of the German state of Lower Saxony. Its 535,932 (2021) inhabitants make it the 13th-largest city in Germany as well as the fourth-largest city in Northern Germany a ...
. Starting in 1855, his early working life was spent in
railroad Rail transport (also known as train transport) is a means of transport that transfers passengers and goods on wheeled vehicles running on rails, which are incorporated in tracks. In contrast to road transport, where the vehicles run on a prep ...
engineering for the
Hanover Hanover (; german: Hannover ; nds, Hannober) is the capital and largest city of the German States of Germany, state of Lower Saxony. Its 535,932 (2021) inhabitants make it the List of cities in Germany by population, 13th-largest city in Germa ...
and Oldenburg state railways, designing some famous bridges and making some of the earliest uses of
steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resist ...
truss A truss is an assembly of ''members'' such as beams, connected by ''nodes'', that creates a rigid structure. In engineering, a truss is a structure that "consists of two-force members only, where the members are organized so that the assembl ...
es. Even during his early railway years, Mohr had developed an interest in the theories of mechanics and the
strength of materials The field of strength of materials, also called mechanics of materials, typically refers to various methods of calculating the stresses and strains in structural members, such as beams, columns, and shafts. The methods employed to predict the re ...
. In 1867, he became
professor Professor (commonly abbreviated as Prof.) is an Academy, academic rank at university, universities and other post-secondary education and research institutions in most countries. Literally, ''professor'' derives from Latin as a "person who pr ...
of mechanics at
Stuttgart Stuttgart (; Swabian: ; ) is the capital and largest city of the German state of Baden-Württemberg. It is located on the Neckar river in a fertile valley known as the ''Stuttgarter Kessel'' (Stuttgart Cauldron) and lies an hour from the S ...
Polytechnic, and in 1873 at
Dresden Dresden (, ; Upper Saxon: ''Dräsdn''; wen, label=Upper Sorbian, Drježdźany) is the capital city of the German state of Saxony and its second most populous city, after Leipzig. It is the 12th most populous city of Germany, the fourth l ...
Polytechnic. Mohr had a direct and unpretentious lecturing style that was popular with his students. In addition to a lone textbook, Mohr published many research papers on the theory of structures and strength of materials. In 1874, Mohr formalised the idea of a
statically indeterminate In statics and structural mechanics, a structure is statically indeterminate when the static equilibrium equations force and moment equilibrium conditions are insufficient for determining the internal forces and reactions on that structure. ...
structure. Mohr was an enthusiast for graphical tools and developed the method, for visually representing stress in three dimensions, previously proposed by
Carl Culmann Carl Culmann (10 July 1821 – 9 December 1881) was a German structural engineer. Born in Bad Bergzabern, Rhenish Palatinate, in modern-day Germany, Culmann's father, a pastor, tutored him at home before enrolling him at the military engineeri ...
. In 1882, he famously developed the graphical method for analysing stress known as
Mohr's circle Mohr's circle is a two-dimensional graphical representation of the transformation law for the Cauchy stress tensor. Mohr's circle is often used in calculations relating to mechanical engineering for materials' strength, geotechnical engine ...
and used it to propose an early theory of strength based on shear stress. He also developed the Williot-Mohr diagram for truss displacements and the Maxwell-Mohr method for analysing
statically indeterminate In statics and structural mechanics, a structure is statically indeterminate when the static equilibrium equations force and moment equilibrium conditions are insufficient for determining the internal forces and reactions on that structure. ...
structures, it can also be used to determine the displacement of truss nodes and forces acting on each member. The Maxwell-Mohr method is also referred to as the virtual force method for redundant trusses. He retired in 1900, yet continued his scientific work in Dresden until his death on 2 October 1918.


See also

* Slope deflection method


Bibliography

* Timoshenko, S. P. (1953), ''History of Strength of Materials''
George A. Lesieutre academic lineage
at www.personal.psu.edu {{DEFAULTSORT:Mohr, Christian Otto 1835 births 1918 deaths People from Wesselburen German civil engineers Engineers from Schleswig-Holstein