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Understanding Truss Structures: Types, Classifications, and Design Theory

This lecture covers the essential aspects of truss structures, focusing on common types and their classification. Key concepts include coplanar trusses, design assumptions, and characteristics such as joints and load application. The discussion emphasizes various truss types: simple, compound, and complex, along with their determinacy and stability conditions. Special attention is given to the calculation of stability, including scenarios of static determinacy and indeterminacy. This outline serves as a foundation for understanding structural engineering principles related to trusses at the Swedish College of Engineering & Technology.

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Understanding Truss Structures: Types, Classifications, and Design Theory

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  1. Truss: Types and Classification Theory of Structure - I Swedish College of engg & tech,wah cantt

  2. Lecture Outlines • Common Types of Trusses (Read from book) • Classification of Coplanar Trusses

  3. Assumptions for Design • All members are connected at both ends by smooth frictionless pins. • All loads are applied at joints (member weight is negligible). • Notes: • Centroids of all joint members coincide at the joint. • All members are straight. • All load conditions satisfy Hooke’s law.

  4. C P C D P C P D A B A B A B new members a d (new joint) b c Classification of Coplanar Trusses • Simple Trusses

  5. simple truss simple truss simple truss simple truss Type 1 Type 2 secondary simple truss secondary simple truss secondary simple truss secondary simple truss main simple truss Type 3 • Compound Trusses

  6. Determinacy b + r = 2j statically determinate b + r > 2j statically indeterminate • Complex Trusses In particular, the degree of indeterminacy is specified by the difference in the numbers (b + r) - 2j.

  7. b + r < 2j unstable b + r 2j unstable if truss support reactions are concurrent or parallel or if some of the components of the truss form a collapsible mechanism Unstable-concurrent reactions Unstable-parallel reactions > • Stability External Unstable

  8. F C O A B D E AD, BE, and CF are concurrent at point O Internal Unstable 8 + 3 = 11 < 2(6)

  9. Example 3-1 Classify each of the trusses in the figure below as stable, unstable, statically determinate, or statically indeterminate. The trusses are subjected to arbitrary external loadings that are assumed to be known and can act anywhere on the trusses.

  10. SOLUTION Externally stable, since the reactions are not concurrent or parallel. Since b = 19, r = 3, j = 11, then b + r = 2j or 22 = 22. Therefore, the truss is statically determinate. By inspection the truss is internally stable. Externally stable. Since b = 15, r = 4, j = 9, then b + r > 2j or 19 > 18. The truss is statically indeterminate to the first degree. By inspection the truss is internally stable.

  11. Externally stable. Since b = 9, r = 3, j = 6, then b + r = 2j or 12 = 12. The truss is statically determinate. By inspection the truss is internally stable. Externally stable. Since b = 12, r = 3, j = 8, then b + r < 2j or 15 < 16. The truss is internally unstable.

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