7.Truss - Truss Theory and Design of Structures I Truss...

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Truss Theory and Design of Structures I What is a truss ? • It is a structural system built from bars taking axial tension or compression. What is a plane truss ? • It is a 2-dimensional truss with all members lying within one plane. Truss Assumptions: • The members are connected at their ends by frictionless hinges. • The members and applied loads all lie within the same plane. • The loads are applied at the joints only. Hence, the members of an ideal truss take up axial forces only (tension or compression)! Truss Method of Joints Method of Joints • This method is based upon the conditions of equilibrium of the forces acting on each joint. • The two equilibrium equations are: Σ F x = 0 Σ F y = 0 This method works when there are up to 2 unknown forces present at each joint considered. Method of Joints Example 1 Determine the member forces 3m 3m 3m A B C D E F 4m 60kN Truss under a point load
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Method of Joints Member forces R C 60kN R F A B C D E F Forces acting on the truss Method of Joints 1. Considering the entire structure as a free body, determine all external reactions at the supports. Taking moment about F, Resolving vertically, 0 6 60 9 = × + c R ) upward ( kN 40 = c R 3m 3m 3m A B C D E F 4m 60kN Truss under a point load R C R F 60 = + F c R R ) upward ( kN 20 = F R Method of Joints 2. Applying equilibrium equations at the desired joint, i.e. support C = 0 y F 0 5 4 40 = + AC F ) n compressio ( kN
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This note was uploaded on 12/01/2010 for the course CIVL 2007 taught by Professor Profchai during the Spring '10 term at HKU.

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7.Truss - Truss Theory and Design of Structures I Truss...

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