The Hoyer-System – A Forgotten Pre-stressed Concrete System up to Date Again

Abstract

Already in the late 1880’s, there were patents for systems (f.e. Jackson and Doehring) which can be seen as pre-stressed concrete. Further system developments followed well into the 1920’s, but all the systems failed because of the steel quality, and of its inherent limited strength. Some researchers (f.e. Wettstein-Boards) used steel wires with small diameters. In the 1920’s and 1930’s, Hoyer utilized very small diameters, called piano wires, as pre-stressing steel, which had a higher strength as the ones used at that time. At the same time, the French engineer Freyssinet established a pre-stressing system that made use of thicker bars. To transfer the high pre-stressed forces to the concrete, defined anchorage points were necessary. In contrast, these anchorage systems were not necessary in the Hoyer system because of the force and surface ratio of each single piano wire (known as the Hoyer effect).