# M3 - CIV100 Mechanics Module 3 Structural Analysis by...

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1 CIV100 – Mechanics Module 3: Structural Analysis by: Jinyue Zhang 2010/10/14 1 Module Objective By the end of this Module you should be able to: Understand what a truss is Know how to find internal forces in a truss using the method of joints using the method of sections Analyze complex structures such as frames and machines

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2 2010/10/14 2 Today’s Objective Understand a simple truss and its assumption Method of joints Examples 2010/10/14 3 What is a Truss? A truss is a structure comprising one or more triangular units constructed with straight members whose ends are pin-connected at joints.
3 2010/10/14 4 What is a Truss? Trusses are a major type of structure consisting of straight members We assume truss members are pin-connected at their ends by frictionless pins Loads are applied only at the joints Thus, member end forces must be collinear and opposite for equilibrium All truss members are 2-force members Members in tension or compression Tension: tends to elongate the member Compression: tends to shorten the member 2010/10/14 5 Rigid/Stable Trusses The simplest form of a rigid or stable truss is a triangle. It is still a simple truss if we consequently connect two members to form an additional triangular element.

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4 2010/10/14 6 Truss Analysis – Method of Joints In order to analyze/design a truss, we need to know the force in each member. 2010/10/14 7 Method of Joints – Procedure for Analysis Understand the structure, obtain all external forces for the whole structure first, including all reaction forces if necessary. Start with a joint having at least one known force and at most two unknown forces. Draw FBD of that joint, label all known and unknown forces. Establish the sense of unknown forces to be in tension. (or you can establish the sense by inspection ) Resolve forces into their x and y components and then apply the two force equilibrium equations. Solve for the unknown forces and verify their correct sense. Continue to analyze each of the other joints, solve those solvable joints (with at most two unknown forces) first, and then check your solution by the last joint.
5 2010/10/14 8 Example 1 Determine the force in each member. Are they in tension or compression? 2010/10/14 9 Example 1 Determine the force in each member. Are they in tension or compression? Pay attention to significant figures!

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6 2010/10/14 10 Example 2 Determine the force in each member. Are they in tension or compression? 2010/10/14 11 Example 2 Determine the force in each member. Are they in tension or compression?
7 2010/10/14 12 Review Questions In the method of joints, typically _________ equations of equilibrium are applied at every joint.

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M3 - CIV100 Mechanics Module 3 Structural Analysis by...

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