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 12 -20 m)

Scissors (span 4 - 6 m)

Compound Fink (span 12 -20 m)

Fan (span 9 -12 m)

TYPICAL BRIDGE TRUSS

Baltimore Bowstring (span 20 - 30 m)

K Truss

Warren

Pratt

Howe

Deck truss railroad bridge over the Erie Canal in Lockport, 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