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UPRVUNL AE ME 2016 Official Paper

Option 2 : Not more than two unknown force members

CT 1: Engineering Mathematics

1084

10 Questions
10 Marks
12 Mins

Method of joint is used to find the unknown forces at the joints in a truss problem

**Method of Joint: **At each joint the forces in the members meeting and the loads acting constitute a system of concurrent forces. Hence, two independent equations of equilibrium can be formed at each joint (Horizontal and Vertical Equilibrium).

**A joint is selected where there are only two unknown forces. First reactions at the support is calculated by considering the equilibrium of the entire truss frame.**Then making the use of two equations at the equilibrium at that joint the two unknown forces are found.

**In method of section**, after determining the reactions a section line is drawn passing through not more than three members in which forces are not known such that that the frame is cut into parts. Each part should be in equilibrium under the action of loads, reactions and forces in the members that are cut by the section line. Equilibrium of any of these two parts is considered and the unknown forces in the members cut by the section line are determined. The system of forces acting on either part of truss constitutes a non-current force system. Since there are only three independent equations of equilibrium there should be only three unknown forces. Hence in this method it is essential that the section line should pass through not more than three members in which forces are not known and it should separate the frame into two parts.

Method of section is preferred over method of joints when

- There is a large truss and force in only few members are required.
- In the situation when method of joints fails to start or proceed with the analysis.