# Kinds of Trusses in Engineering Mechanics
-
Planar Truss
-
The two-dimensional planar truss lies in a single plane and is typically used to form roofs, floors and bridges. The height between the upper and lower parallel members of a truss make it an efficient structure, since a solid beam or girder of the same height would increase the weight and cost of the structure. One popular type of planar truss is the pitched truss, which has a triangular overall shape and is often used in roof construction. The parallel chord truss, often called the flat truss, gives strength to floor construction.
Space Frame Truss
-
The three-dimensional space frame truss consists of non-collapsible tetrahedral forms composed of six members pinned together at four nodes. Linked together, these tetrahedral units commonly form the framework of objects such as power line supports and fire tower lookouts.
Pratt Truss
-
One of the most popular planar trusses in use is the Pratt truss which was patented by two railway engineers in 1844. This practical truss lends itself to carrying vertical, static dead loads and engineers have found it useful in bridge building. It has survived the changes in construction materials from wood to cast iron and finally to steel. In 1903, the Wright brothers built the Wright Flyer from spruce and ash covered with muslin; their craft used Pratt trusses, the characteristics of which encouraged a lower aerodynamic drag due to its light weight, strength and flexibility.
Bowstring Truss
-
During World War II, engineers developed the bowstring truss design to uphold the curved roofs of aircraft hangars and other military structures. Unfortunately the bowstring truss roof has earned a dangerous reputation due to its instability and the corresponding risk of collapse. During fires, several firefighters have been crushed by collapsing roofs. These trusses were popular in bridges during the 1870s, but gradually faded away due to structural problems; very few exist today, and are now the rarest type of truss bridges in existence.
-
