COMMON TYPES OF TRUSSES

A truss is one of the major types of engineering structures which provides a practical and economical solution for many engineering constructions, especially in the design of bridges and buildings that demand large spans.

A truss is a structure composed of slender members joined together at their end points.
The joint connections are usually formed by bolting or welding the ends of the members to a common plate called gusset.
Planar trusses lie in a single plane & is often used to support roof or bridges.
ROOF TRUSS
They are often used as part of an industrial building frame.
Roof load is transmitted to the truss at the joints by means of a series of purlins.

To keep the frame rigid & thereby capable of resisting horizontal wind forces, knee braces are sometimes used at the supporting column.

BRIDGE TRUSS
The main structural elements of a typical bridge truss are shown in figure. Here it is seen that a load on the deck is first transmitted to stringers, then to floor beams, and finally to the joints of the two supporting side trusses.
 
The top and bottom cords of these side trusses are connected by top and bottom lateral bracing, which serves to resist the lateral forces caused by wind and the sidesway caused by moving vehicles on the bridge.
Additional stability is provided by the portal and sway bracing. As in the case of many long-span trusses, a roller is provided at one end of a bridge truss to allow for thermal expansion.

In particular, the Pratt, Howe, and Warren trusses are normally used for spans up to 61 m in length. The most common form is the Warren truss with verticals.
For larger spans, a truss with a polygonal upper cord, such as the Parker truss, is used for some savings in material. 
The Warren truss with verticals can also be fabricated in this manner for spans up to 91 m.

The greatest economy of material is obtained if the diagonals have a slope between 45 ° and 60 ° with the horizontal. If this rule is maintained, then for spans greater than 91 m, the depth of the truss must increase and consequently the panels will get longer.
This results in a heavy deck system and, to keep the weight of the deck within tolerable limits, subdivided trusses have been developed. Typical examples include the Baltimore and subdivided Warren trusses.
The K-truss shown can also be used in place of a subdivided truss, since it accomplishes the same purpose.