1. Structural Analysis-I
Dr. Ali Tayeh
Second Semester

2. Lecture 5
Trusses

3. Trusses in Building

4. Trusses Types for Building

7. Truss Bridge

8. Truss Bridge Types

10. Classification of coplanar Truss
1. Simple Truss

11. 2. Compound Truss

12. 3. Complex Truss
لا تنطبق علية شروط الجمالون البسيط ولا المركب

13. Determinacy For plane truss If b+r = 2j statically determinate
If b+r > 2j statically indeterminate
Where
b = number of bars
r = number of external support reaction
j = number of joints
Determinacy

14. Stability For plane truss If b+r < 2j unstable
The truss can be statically determinate or indeterminate (b+r >=2j) but unstable in the following cases:
External Stability: truss is externally unstable if all of its reactions are concurrent or parallel
Stability

15. Internal stability: Internally stable Internally unstable
b + r = 2 j Statically determinate b + r > 2 j Statically Indeterminate b + r < 2 j Unstable
Internally unstable

16. Classify each of the truss as stable , unstable, statically determinate or indeterminate.
b + r = 2 j Statically determinate b + r > 2 j Statically Indeterminate b + r < 2 j Unstable
b = 19
, r = 3
, j = 11
b = 15
, r = 4
, j = 9
b + r = = 22
b + r = = 19
2 j = 2 (11) = 22
2 j = 2 (9) = 18
Statically determinate & Stable.
Statically Indeterminate & Stable.

17. b + r = 2 j Statically determinate b + r > 2 j Statically Indeterminate b + r < 2 j Unstable
b = 9
, r = 3
, j = 6
b = 12
, r = 3
, j = 8
b + r = = 12
b + r = = 15
2 j = 2 (6) = 12
2 j = 2 (8) = 16
Statically determinate & Stable.
Unstable

18. The Method of Joints STEPS FOR ANALYSIS
1. If the support reactions are not given, draw a FBD of the entire truss and determine all the support reactions using the equations of equilibrium.
2. Draw the free-body diagram of a joint with one or two unknowns. Assume that all unknown member forces act in tension (pulling the pin) unless you can determine by inspection that the forces are compression loads.
3. Apply the scalar equations of equilibrium,  FX = 0 and FY = 0, to determine the unknown(s). If the answer is positive, then the assumed direction (tension) is correct, otherwise it is in the opposite direction (compression).
4. Repeat steps 2 and 3 at each joint in succession until all the required forces are determined.

19. The Method of Joints

20. Example 1
Solve the following truss

23. Group Work
Determine the force in each member

24. Zero Force Member
1- If a joint has only two non-collinear members and there is no external load or support reaction at that joint, then those two members are zero-force members
non-collinear غير واقعين على نفس الخط

25. Zero Force Member
2- If three members form a truss joint for which two of the members are collinear and there is no external load or reaction at that joint, then the third non-collinear member is a zero force member.

26. Example 2
Find Zero force member of the following truss

27. END
ANY QUESTION?