September 19th, 2017
Before steel came into general use during the latter part of the 19th century, curved structures were frequently constructed from iron, which is cast in liquid form in a curved profile or built up from wrought iron components, either with shaped web plates or in the form of lattice trusses. Because wrought iron was very soft, blacksmiths could curve small components by hot forging.
During the 20th century, rolled steel joists were curved by metal benders for use as colliery arches to support underground workings. Hydraulic presses were used initially to curve the joists but eventually three-roll bending machines were introduced for bending metal. Because joists have very thick webs, they are not susceptible to buckling during the bending operation.
Metal benders were also used in the fabrication of ship hulls. As early as 1910, bending equipment incorporating rollers were used to curve bulb flats, bulb angles and tees for marine use. During the period from 1930 to 1950, small curved steel components were also used in relatively simple building structures. Nissen huts, aircraft hangers and Dutch barns often had a supporting structure of curved steel angles, tees or small rolled I sections.
From the late 1940s, universal beams (I sections with parallel flanges) came into general use. These parallel flange sections, which had relatively thin webs (in comparison with joists), were difficult to curve about the major axis because the force needed to bend a complete beam was actually greater than that which caused local buckling of the web. In the mid-1970s, steel bending companies produced bending machines with additional rolls to support the web were introduced. This development allowed steel benders to curve large universal beams about the major axis economically and accurately and had a significant influence on the design of curved steel structures and metal bending became a common feature in the construction industry. Over the course of time, induction bending, a hot bending process that was developed originally for bending process pipework, has also been adapted to suit the needs of structural steelwork.
During the last two decades of the 20th century, the demand for curved steel members in building structures increased considerably. The focus of capital investment on commercial rather than industrial buildings, and the resultant construction of new offices, airport terminals, stations, superstores and leisure facilities provided the market environment in which structural steel flourished and metal bending became a viable business in its own right, offering bending of metal in a variety of shapes and offering Architects a way of achieving their visions.
More specifically, with the introduction of equipment with the capability of bending steel/metal accurately and economically, the inherent advantages of steel framed construction were complemented by new design possibilities that had previously been confined to alternative forms of construction or limited by cost considerations. The main advantage of using curved members is the undoubted aesthetic appeal of curved steel sections and tubes, which has opened up new horizons for the creative design of steel structures.