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What is Truss??

Introduction

  • A truss is a structure comprising one or more triangular units constructed with straight members whose ends are connected at joints.
  • A framework, typically consisting of rafters, posts, and struts, supporting a roof, bridge or other structure.
  • A truss is an articulated structural with hinged or ball and socket. It is an assemblage of slender bars fastened together at their ends by smooth pins or ball and socket joints acting as hinges.
  • If all the bars lie in a plane, the structure is a planar truss.

Analysis of Trusses

While analyzing a truss structure, a person needs to assume some things to keep things simple:

  • The joint is where the entire load is applied, and all other forces on the member are to be neglected.
  • The weight of a member is very insignificant to the amount of load that has been applied to it. Hence, it will not be considered in future calculation. However, some methods may take in account half of the weight of the member as acting on each individual joint of the member.

Different Types of Trusses

  1. Perfect Truss
  2. Imperfect Truss

Perfect Truss

  • A pin jointed truss which has get just sufficient number of members to resist the load without under-going any deformation in shape is called a perfect truss.
  • Triangular frames is the simplest perfect truss and has three joints and three members.
  • There is a mathematical formula by which we decide the given truss is perfect or imperfect.
  • m=2j-r

Imperfect Truss

  • A truss which doesn’t satisfies the relation m=2j-r is called an imperfect truss.
  • Imperfect Deficient Truss: A truss which satisfies the relation m<2j-r is called a deficient truss. It is unstable and may collapse under external forces.
  • Imperfect Redundant Truss: A truss which satisfies the relation m>2j-r is called a redundant truss. It can’t be completely analysed by static equilibrium condition, therefore it is an indeterminate structure.

Assumption for a perfect truss

  • All the members of truss are straight and connected to each other at their ends by friction pins.
  • All external forces are acting only at pins.
  • All the members are assumed to be weightless.
  • All the members of truss and external forces acting at pins lies in same plane.
  • Static equilibrium condition is applicable for analysis of perfect truss.

Characteristics of trusses

  • A truss consists of straight members connected at joints, traditionally termed panel points. Trusses are composed of triangles because of the structural stability of that shape and design. A triangle is the simplest geometric figure that will not change shape when the length of the sides are fixed. In comparison, both the angles and the lengths of a four-sided figure must be fixed for it to retain its shape. The joint at which a truss is designed to be supported is commonly referred to as the munster point.

Truss bridge connections

  • The pieces of the framework of a truss bridge are held together by connections. Most connections on historic bridges are either riveted or pinned.
  • Pinned Connections can be identified by the bolt-like object called a pin going through the loops of the members. They tend to show up on bridges from the first half of the truss bridge era.
  • Riveted Connections are identified by a ‘gusset plate’ which diagonals and vertical members are riveted to, and no pin is present. These connections tend to show up in the second half of the truss bridge era.

Analysis of frame

  • A frame is a structure made of several bars/rods welded/riveted together.
  • The bars are angle irons/channels members.
  • On application of load on to the structure, the members remain loaded with tensile/compressive load.
  • Members under tension.
  • Members under compression.
  • The structure formed by the members is called ‘truss’.

Stresses in a frame

  • Under application of load the structure tends to deform. The material of the frame tends to keep the frame rigid.
  • An internal resistive force is set in the material.
  • Load can be pull/push (tensile/compressive).
  • For joints to be in equilibrium the members may carry zero load/tensile/compressive load.

Conclusion

  • After study about truss, I conclude that concept of trusses are very useful in our real life, because concept of truss are help us to make bridge, roof, and tower, etc. so trusses are very useful for us, it also have some disadvantage. In truss bridge, it takes up more space and can some-times become a distraction to drivers. It also have higher maintenance demand of all joint and fitting more calculation to determine that it will take the maximum load.

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