On January 21 of the year 1890, U.S. Patent No. 419,897 issued to Kansas engineer, William E. Stearns for a truss bridge that became known as the Stearns Truss.
A truss bridge has a deck that is supported by a superstructure that is formed by a truss, i.e., a structure formed by elongated members (such as wood beams and/or metal girders) that are connected together to (typically) form a series of triangles. Truss bridges were used extensively in the 19th century and early 20th century to form America's transportation infrastructure because they used materials efficiently to carry relatively large loads. Engineers, such as Stearns, strove to continuously improve this efficiency by inventing new designs that used less material, which would make them less expensive to build. A number of these designs were patented by their inventors, such as Stearns.
Depending on the required length of the bridge, the Stearns Truss characteristically had on each side of the bridge, either two adjacent trapezoidal outer panels or two trapezoidal outer panels separated by a rectangular center panel. In the version with only outer panels, the Stearns Truss had, on each side, a single vertical post that was shared by the two outer panels, while in the version with center panels, the Stearns Truss had, on each side, two vertical posts that were shared between the center panel and the two outer panels, respectively. Each outer panel had four struts: one vertical outer strut, two diagonal struts that extended from the top chord to the bottom chord in an inward direction and one diagonal strut that extended from the top chord to the bottom chord in an outward direction. The center panel also had four struts: two that formed a V-shape and two that formed an X-shape, with the V-shape intersecting the X-shape.
Interestingly, the Stearns patent was not directed to the features by which the Stearns Truss is distinguished from other truss bridges, i.e., the arrangement of the vertical posts and the diagonal struts described above. Instead, the Stearns patent was primarily directed to the dual girder construction of the top chord. In addition, the distinguishing features of the Stearns truss described above were not fully shown in the patent. More specifically, the outwardly-directed diagonal struts in the outer panels were not shown. These missing struts have been added (in red) to the marked-up patent drawing shown below.
A truss bridge has a deck that is supported by a superstructure that is formed by a truss, i.e., a structure formed by elongated members (such as wood beams and/or metal girders) that are connected together to (typically) form a series of triangles. Truss bridges were used extensively in the 19th century and early 20th century to form America's transportation infrastructure because they used materials efficiently to carry relatively large loads. Engineers, such as Stearns, strove to continuously improve this efficiency by inventing new designs that used less material, which would make them less expensive to build. A number of these designs were patented by their inventors, such as Stearns.
Depending on the required length of the bridge, the Stearns Truss characteristically had on each side of the bridge, either two adjacent trapezoidal outer panels or two trapezoidal outer panels separated by a rectangular center panel. In the version with only outer panels, the Stearns Truss had, on each side, a single vertical post that was shared by the two outer panels, while in the version with center panels, the Stearns Truss had, on each side, two vertical posts that were shared between the center panel and the two outer panels, respectively. Each outer panel had four struts: one vertical outer strut, two diagonal struts that extended from the top chord to the bottom chord in an inward direction and one diagonal strut that extended from the top chord to the bottom chord in an outward direction. The center panel also had four struts: two that formed a V-shape and two that formed an X-shape, with the V-shape intersecting the X-shape.
Interestingly, the Stearns patent was not directed to the features by which the Stearns Truss is distinguished from other truss bridges, i.e., the arrangement of the vertical posts and the diagonal struts described above. Instead, the Stearns patent was primarily directed to the dual girder construction of the top chord. In addition, the distinguishing features of the Stearns truss described above were not fully shown in the patent. More specifically, the outwardly-directed diagonal struts in the outer panels were not shown. These missing struts have been added (in red) to the marked-up patent drawing shown below.
The Stearns Truss used fewer vertical posts than its conventional predecessor, the Pratt Truss. For example, a Stearns Truss with center panels used only four vertical posts (two for each side), whereas a Pratt Truss, with the same span, would use ten vertical posts (five for each side). However, the vertical posts of the Stearns Truss had to be taller than those of the Pratt Truss. Due to reduction in the number of vertical posts that were required, the Stearns Truss was claimed to use over twelve percent less material than the Pratt Truss. However, this claim is suspect and apparently did not take into account the extra material required for the top chord, the extra struts and the taller vertical posts. Whether caused by this illusory savings in material or, more likely, its reduced stability (vis-a-vis the Pratt Truss), the Stearns Truss was not widely adopted.
While not many Stearns Truss bridges were built, one Stearns Truss bridge still exists. The bridge shown below, originally known as Pulaski County Bridge No. 31, was erected in 1905 over the Big Monon Ditch in Pulaski County, Indiana. In 2006-2007, the bridge was rescued from proposed demolition and moved to the Wabash and Erie Canal park in Carroll County, Indiana, and is now known simply as the "Blue Bridge".
While not many Stearns Truss bridges were built, one Stearns Truss bridge still exists. The bridge shown below, originally known as Pulaski County Bridge No. 31, was erected in 1905 over the Big Monon Ditch in Pulaski County, Indiana. In 2006-2007, the bridge was rescued from proposed demolition and moved to the Wabash and Erie Canal park in Carroll County, Indiana, and is now known simply as the "Blue Bridge".
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