Simple beam of 50-foot span with three independent trussing systems. Bollman’s use of this method of support led to the development of his bridge truss. This drawing is of a temporary span used after the timber bridge at Harpers Ferry was destroyed during the Civil War. (In Baltimore and Ohio Collection, Museum of History and Technology.)
There´s always this ¨tension¨ between architects and civil engineers, they say that architects do not think too much about structural issues in defense of aesthetics. This is not true, at least for some of us.
Then, we say engineers design without aesthetic principles.
Today, I´ve been enjoying Contributions from The Museum of History and Technology: Paper 36.The Engineering Contributions of Wendel Bollman by Robert M. Vogel and I´d like to share some nice technical designs of old trusses and bridges.
Bollman’s original patent drawing, 1851. (In National Archives, Washington, D.C.)
Bollman skew bridge at Elysville (now Daniels), Maryland, built in 1853-1854. (Photo courtesy of Maryland Historical Society.)
¨The development of structural engineering has always been as dependent upon the availability of materials as upon the expansion of theoretical concepts. Perhaps the greatest single step in the history of civil engineering was the introduction of iron as a primary structural material in the 19th century; it quickly released the bridge and the building from the confines of a technology based upon the limited strength of masonry and wood. Wendel Bollman, self-taught Baltimore civil engineer, was the first to evolve a system of bridging in iron to be consistently used on an American railroad, becoming one of the pioneers who ushered in the modern period of structural engineering.¨ Wendel Bollman’s name survives today solely in association with the Bollman truss, and even in this respect is known only to a few older civil and railroad engineers. The Bollman system of trussing, along with those of Whipple and Fink, may be said to have introduced the great age of the metal bridge, and thus, directly, the modern period of civil engineering. Bollman’s bridge truss, of which the first example was built in 1850, has the very significant distinction of being the first bridging system in the world employing iron in all of its principal structural members that was used consistently on a railroad. The importance of the transition from wood to iron as a structural and bridge building material is generally recognized, but it may be well to mention certain aspects of this change. The tradition of masonry bridge construction never attained the great strength in this country which it held in Europe, despite a number of notable exceptions. There were several reasons for this. From the very beginning of colonization, capital was scarce, a condition that prevailed until well into the 19th century and which prohibited the use of masonry because of the extremely high costs of labor and transport. An even more important economic consideration was the rapidity with which it was necessary to extend the construction of railways during their pioneer years. Unlike the early English and European railways, which invariably traversed areas of dense population and industrial activity, and were thus assured of a significant financial return almost from the moment that the first rail was down, the[Pg 80] Baltimore and Ohio and its contemporaries were launched upon an entirely different commercial prospect. Their principal business consisted not so much in along-the-line transactions as in haulage between principal terminals separated by great and largely desolate expanses. This meant that income was severely limited until the line was virtually complete from end to end, and it meant that commencement of return upon the initial investment was entirely dependent upon the speed of survey, graduation, tunneling, and bridging.¨
North Street (now Guilford Avenue) bridge, Baltimore. In this transitional composite structure cast iron was used only in the relatively short sections of the upper chord. For the long unsupported compression members of the web system, standard wrought-iron angles and channels were built up into a large section. The decorative cast-iron end posts were non-structural. (Photo in the L. N. Edwards Collection, Museum of History and Technology.)
Chicago, Burlington and Quincy Railroad bridge over Quincy Bay (branch of the Mississippi River) at Quincy, Illinois. The pivot draw-span was formed of two Bollman deck trusses supported at their outer ends by hog chains. The bridge was built in 1867-1868 by the Detroit Bridge and Iron Co., Bollman licensee. (Clarke, Account of the Iron Railway Bridge ... at Quincy, Illinois.)
Patapsco River crossing of the Baltimore and Ohio between Thistle and Ilchester, Maryland. (Photo 695, Baltimore and Ohio Collection, Museum of History and Technology.)
Read the full paper: