• Measurement of bar forces (ties and Rafter).
  • Calculation of bar forces by the method of joints.
  • Comparison: measurement result-calculation-graphical method.


  • Resolution of forces in a single plane, statically determinate system.
  • 3 pin joints, 2 of which serving as supports one fixed and one free longitudinal.
  • 3 bars each fitted with a force gauge (compression & Tensile) element and force markers.
  • 3 elements with force gauges.
  • 2 rafters with compression gauges and fixed length, 1tie with variable length.
  • Different angles adjustable between bars.

This apparatus is used to determine the deformation of various elements of a bar structure when they experience weight. The apparatus consists of base structure. The base structure provides support to the truss. The truss is made of three metallic elements connected in a triangular shape. When load is applied in the bar structure, its members undergo some strain. Load is applied from the top of the truss by using a hangar. Each of the metallic member, making up the truss, has a force gauge attached to it so that force in individual element can be determined when some load is applied. The apparatus shown represents a simple roof truss bar structure. In the single plane system the bars are only subjected to compressions and tensions. Loads are applied only to the nodes. The unit comprises three members that are joined together using node point such that the joints are free to move. A longitudinally adjustable base member permits the structure to be constructed with different angles. The bars engage in the nodes by quick locks. Two of the node points also form the supports (fixed and free with bearings) and are clamped to the sturdy aluminum section base frame. The external load is applied to the upper nodal point by means of weights. The bar forces occurring are measured directly on force gauge in the middle of the bar. The method of joints enables the bar forces to be determined by formulating a system of equations.