This tutorial describes force method to determine internal forces in truss members.
What is a Truss?
Truss is a structure having bar elements connected by pins. We assume that loads are applied only at nodes. We also assume that these pins are friction less. These assumptions ensures that there is no shear or moment developed in the bars and only force is axial force. So a truss element can either elongate or shorten depending on the type of force.
Remember that in real structures there is no such things as friction less pins so there can be some moment or shear developed in the real structure but its value is nominal so we can ignore it. Different Truss configurations are used mainly in Bridges and Building Roofs.
Video Courtesy: Dr. Structure
Method Of Joints
In this video method of joints is used to determine the internal forces of truss elements. Remember that this method is valid for statically determinate trusses as shown in the video. In this method we proceed joint by joint.
Equilibrium is applied on each joint and unknown forces are calculated. At the end Free body diagram is drawn to show respective bar element forces.