Civil Engineering ► Structural Analysis ► Truss Analysis Methods and Introduction
Introduction to Simple Truss Analysis 

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1. Truss Analysis Method of joints

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Zeroforce members

Truss analysis using the method of joints is greatly simplified if one is able to determine those members which support no loading (zeroforce members)

These zeroforce members are used to increase stability of the truss during construction and to provide support if the applied loading is changed

If only two members form a truss joint and no external load or support reaction is applied to the joint, the members must be zeroforce members

If three members form a truss for which two of the members are collinear, the third member is a zeroforce member provided no external force or support reaction is applied.
2. Method of sections for trusses

Based on the principle that if a body is in equilibrium, then any part of the body is also in equilibrium

Section or “cut” the truss through the members where the forces are to be determined

Before isolating the appropriate section, it may be necessary to determine the truss’s external reactions (then 3 equations equations of equilibrium can be used to solve for unknown member forces in the section)

Draw the freebody diagram of that part of the sectioned truss that has the least number of forces acting on it

Establish the sense of the unknown member forces

Apply 3 equations of equilibrium trying to avoid equations that need to be solved simultaneously

Moments should be summed about a point that lies at the intersection of the lines of action of two unknown forces

If two unknown forces are parallel – sum forces perpendicular to the direction of these unknowns
Procedure for analysis
Frames and Machines

Structures are often composed of pinconnected multi force members

Frames are generally stationary and are used to support loads

Machines contain moving parts and are designed to transmit and alter the effect of forces

Can apply the equations of equilibrium to each member of the frame or machine to determine the forces acting at the joints and supports (assuming the frame or machine is properly constrained and contains no more supports or members than are necessary to prevent collapse)

Construct applicable freebody diagrams

Draw an outline of the shape

Show all forces or couple moments that act on the part

Indicate dimensions needed for determining moments

Identify all two force members in the structure

All loadings are applied at the joint

Members are joined together by smooth pins

Members have two equal but opposite forces acting at their points of application

The line of action of the forces are along the axis of the members

Forces common to any two contacting members act with equal magnitudes but opposite sense on the respective members

Apply the equations of equilibrium
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