All About Truss Bridges
You may have very well driven over one since it's a common type of bridge. Truss bridges are one of the older modern bridge styles. They're designed simply and make efficient use of materials, making them cost-effective to construct as well.
What Are Truss Bridges?
You may be wondering what a truss is to begin with. A truss is a structure that's made up of triangular units connected together at joints called nodes. These units are slender and straight. Trusses aren't only found in bridges but also in roofs. A truss bridge connects elements together by using compression or tension or both. Much of the engineering of a truss bridge applies Newton's laws of motion and considers the way each element of the bridge will be affected by what will be crossing over it.
A Little History on Truss Bridges
Most of the early American truss bridges (early 19th century) were made of a combination of wood and iron and many were covered to protect them. Some wooden bridge truss plans of that period didn't require a lot of skill to build and since wood was readily available, they were more economic to construct at the time than iron bridges. Of course, as time went on that would change. Iron bridges started to replace wooden bridges by the 1870s and then just a decade or so later in the 1880s and 1890s, steel became a more popular bridge material. Bridges built during the height of the truss bridge -- from the 1870s to around the 1930s -- still stand in some places. However, many have had to be replaced with new bridges.
As things go, as truss bridges became more and more popular, several companies cropped up trying to push their bridge designs over their competitors. Some bridge styles such as the bowstring truss design eventually became less popular as time proved it to be inferior to other designs. Because this style of bridge became so popular, states eventually (around the 1910s) adopted a standard truss bridge design. The steel warren pony truss bridge was one of these. Through the 1930s some states such as Pennsylvania continued to use the truss bridge as a standard bridge while other states, including Michigan, moved on to other bridge designs.
There are many types of truss bridges and each is a little different in style and what it is made to withstand. Some types of truss bridge were good as railway bridges (the Pratt truss for example) and others were primarily used by the military to handle heavy loads and machinery like tanks (the Bailey bridge for example). Other styles of truss bridge include the Howe truss, the K truss, the Bowstring Arch truss, and the King Post truss. Each style has unique features.
Truss bridges were an integral part of the American landscape for decades and can still be seen in some parts of the country today. Unfortunately, some have had to be replaced and some are still standing but no longer in use. Covered truss bridges are especially rare today. They are a unique feature of cities and towns and represent changes in engineering and industry that still affect us today.
