TRUSS

Definition of a Truss Trusses are framed structures composed of short, straight pieces joined to form a series of triangles which are made of wood or steel. Bolted or welded connections are assumed to be pinned together. Only two-force members are considered. When forces tend to pull the member apart, it is in tension. When the forces tend to compress the member, it is in compression.

Large truss are constructed by attaching several triangles together. The basic building block of a truss is a triangle.

A truss consisting of coplanar members are called plane trusses. Eg:- Trusses on both sides of bridges, Roof trusses. If a truss is made up of non-coplanar members, it is referred to as space truss. Eg: - Tower of electric power transmission system

Plane truss Space truss

CLASSIFICATION OF TRUSSES Based on stability Based on the use Based on the geometry Based on the material

There is a simple relationship between the number of joints (j) and the number of members (m) is established as where, m is number of members, j represents the number of joints and 3 represents the external support reactions. m = 2j-3

If m = 2j – 3 If m < 2j – 3 If m > 2j – 3 Perfect truss Deficient truss Redundant truss

CLASSIFICATION OF TRUSSES Based on stability Based on the use Based on the geometry Based on the material

Roof truss/ pitched truss – These are characterized by their triangular shape They are most often used for roof They will support the roof covering and rests on the wall Bridge truss / flat truss – They got its name from its parallel top and bottom chords It is often used as deck in bridge

CLASSIFICATION OF TRUSSES Based on stability Based on the use Based on the geometry Based on the material

Based on the geometry, trusses can be classified as King post Queen post Pratt Howe Warren Fink Fan K Truss Baltimore Bowstring

TYPICAL ROOF TRUSS

King Post Queen Post Span 4 – 6 m 4 – 6 m

Compound Howe (span m) Scissors (span m) Compound Fink (span m) Fan (span m)

TYPICAL BRIDGE TRUSS

Baltimore Bowstring (span m) K Truss Warren

Pratt Howe

Deck truss railroad bridge over the Erie Canal in Lockport, New YorkErie CanalLockport, New York

Howrah Bridge, Kolkota

CLASSIFICATION OF TRUSSES Based on stability Based on the use Based on arrangement of the members Based on the material

Wooden truss  Made of well seasoned timber  Most commonly used are king post truss (span 6 – 9 m) and Queen post trusses (span 9 – 14 m)

Steel truss Fabricated by connecting steel sections suitably either by riveting or welding Light weight structures Can be easily connected Used for very large spans Can be easily erected