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Understand the principles of truss structures and analysis using the Method of Joints. Learn to identify forces, solve unknowns, and ensure equilibrium in 2D and 3D trusses. Dive into the significance of assumptions and complete solutions for internal forces. Enhance your engineering knowledge today.
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Truss Structure: A structure with slender members pin-connected at their ends, referred as joints, to carry loads at the joints. ES2501: Statics/Unit 16-1: Truss Analysis: the Method of Joints To be a truss: - Nodal loading only; - All joints pin-connected Hinged support Roller support Real physical Truss Modeling Joint/Node Planar Truss (2D) Statically determinate Truss Truss Truss Space Truss (3D) Statically indeterminate Truss
Significance of Assumptions in Truss Analysis: Each member in a truss is a two-force member. ES2501: Statics/Unit 16-2: Truss Analysis: the Method of Joints Force of the rest of the truss on member AB through a pin at A A A B B Force of the rest of the truss on member AB through a pin at B Two-force member in equilibrium A Two forces must have the same amplitude, opposite direction and along the same line B - Nodal loading only; - No moments at node
ES2501: Statics/Unit 16-3: Truss Analysis: the Method of Joints Sign Convention: In analysis, always starts with the assumed positive direction. Then, a positive result indicates tension and a negative value means compression.
Method of Joints (Nodal Analysis): Step 1: Find support reactions; Step 2: Draw a free-body diagram and list equilibrium equations for each joint; Step 3: Select independent equations to solve unknowns. ES2501: Statics/Unit 16-4: Truss Analysis: the Method of Joints Example 1: Reactions: Free-body diagram of the truss, see the lift figure Take moment about a point with the most unknown forces Equilibrium Equations at Joints: Equilibrium at C: “+” --- tension “-” --- compression Sign convention
Example 1: Equilibrium Equations at Joints (con’d): ES2501: Statics/Unit 16-5: Truss Analysis: the Method of Joints Equilibrium at C: Zero-force member Equilibrium at A: Equilibrium at D: Equilibrium at B: Zero-force member Automatically satisfied
Comments: ES2501: Statics/Unit 16-6: Truss Analysis: the Method of Joints • Method of joints uses equilibrium of joints to list • necessary equations for unknowns; • Method of joints provides complete solution for • internal forces for all members • Identifying zero-force members in a truss may • simplify analysis • Sign convention: Use tension as the conventional • direction for the internal force of any member • “+” --- tension; “-” --- compression • Presentation of results: • Mark the results on the truss • If solving problem manually start with finding the reactions and list • equilibrium equations for nodes with least number of unknowns.
Formulate a set of simultaneous linear equations for • a computer solution Comments (con’d): ES2501: Statics/Unit 16-7: Truss Analysis: the Method of Joints Re-collection of equilibrium equations For joint C For truss For joint A: For joint E For joint D: For joint B: Select independent 10 equations for 10 unknown: Computer solution Note: there for more than 10 equations but only 10 of them are linearly independent