ENSC1002StaticsLectureNotes.pdf

# For example this truss has 3 external reactions so it

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For example This truss has 3 external reactions, so it is externally statically determinate. It has members and joints. i.e we can solve for reactions in the usual way

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Week 11 Lecture 1 6 i.e. all forces acting are. If we wanted to find the forces in Members EF, BE and BC using the method of joints, we would need to start at Joints A or D and work in towards the centre of the truss. However, using the method of sections, we make an imaginary cut down the middle of the truss Note that each half of the truss will not "know" that it has been cut and the other half "removed" if we apply forces on the cut surface equal to the internal forces in cut members.
Week 11 Lecture 1 7 We do not know the magnitude of the forces on the cut surfaces. Nor do we know if they act toward or away from the cut. To begin with we assume the forces act away from the cut as if the members are acting in tension. We can now treat each part of the structure as an independent object and apply our equations of equilibrium to solve. Consider the left half of the structure. There is only one unknown force in the vertical direction. i.e. the vertical component of Fbe. One equation one unknown… can solve

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Week 11 Lecture 1 8 What about Fef and Fbc. Using LHS
Week 11 Lecture 1 9

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Week 11 Lecture 1 10 Now check result by working on Left hand side
Week 11 Lecture 1 11

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Week 11 Lecture 1 12 Practice questions Complete the following questions in preparation for next week's (week 6) quiz. is the following truss statically determinate? is the following truss stable/stat det or stat indet? Determine the forces in members GH and CG for the truss loaded and supported as shown below. (Hint, if you make a cut through GH, CG and CD and consider only the left side, you do not need to know the reactions at supports E and F)
Week 11 Lecture 2 1 Final Truss Example

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Week 11 Lecture 2 2
Week 11 Lecture 2 3

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Week 11 Lecture 2 4
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