Kinds of Truss Bridges
There are numerous forms of truss bridges that depend upon the topography and the purpose to be obtained by the bridge. The common types of truss bridges are as explained below:
The Howe truss consists of diagonal and vertical elements. The diagonal elements slope towards the bridge center in an upward direction. The vertical elements are under tension. This is a rare type of truss bridge originally patented in 1840 by William Howe. Famous examples are the Jay Bridge in New York and the Sandy Creek Covered Bridge in Missouri
This kind of bridge uses a lens-shape truss. An upper arch curves up and then down, and a lower one curves down and then up. The two arches meet at the same end points. Examples of this bridge include the Royal Albert Bridge in UK and the Smithfield Street Bridge in Pennsylvania.
This bridge is normally utilized to cover obstacles by the military tanks and other equipment. It can be constructed without the need of heavy tools or machinery.
The bridge design is complex, and the construction requires extensive use of heavy equipment. The bridge elements under tension are reduced in number.
Bowstring Arch Truss
This bridge was patented in 1840 by S. Whipple. The main characteristic here is that the vertical loads on the thrust arches are transmitted along the arc path. At the end of the arch, the thrust is resolved into vertical and horizontal components.
In this bridge, the upper chords are all of equal length and the lower chords are longer than the corresponding upper chord. Because of this difference, each panel is not square. This truss design was patented by George H. Pegram in 1885. Only ten Pegram bridges remain in the United States, and seven of them are in Idaho.