Genealogy of Howe Truss Design

Genealogy of Howe Truss Design. . , 1. Corduroy Bridge , The corduroy bridge was the earliest of the American bridges and consisted of logs laid across supporting timbers. These were effective for narrow streams, but would have had a short life expectancy. , 2. King Post , The king post truss added strength to the bridge, but length was still limited by the length of the timbers. , 3. Boxed Trusses , Before covered bridges became common, trusses were sometimes boxed in to protect them from the weather. This helped extend the life of the bridge. , 4. Queen Post , The development of the queen post truss allowed the construction of a longer bridge that could span a wider river. However, the length of the bridge was still limited as the queen post could not be expanded and still retain its strength. , 5. Howe Truss , In America the Howe truss, combining wood and metal, was the most popular truss system among railroads during the latter half of the 19th century because the vertical iron rods could be adjusted to remove the sagging of old age and because a 100 foot model could be easily erected in 24 hours, with roof and sides added while in use. Although this design was an improvement on the all-wood bridge, a number of infamous railroad disasters were caused by structural failures in Howe trusses. , 6. A Covered Bridge , Any of the early designs easily lent themselves to having a roof and sides added for protection and strength. The result was a covered bridge.