ME 221 Statics
Lecture #33
Section 6.9
ME221
Lecture 33
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Homework #11
Chapter 6 problems:
– 2, 3, 6 & 7 – Method of Joints
– 32, 36, 47 & 53 – Method of Sections
– 68 & 75
• Due Friday, November 21
ME221
Lecture 33
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Homework #12
Chapter 8 problems:
– 1, 2, 4, 8 & 15
Due Monday, December 1
ME221
Lecture 33
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Quiz #7
Friday, November 21
Analysis of Structures
Method of Joints or
Method of Sections
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Frames and Machines
• Frames and machines have at least one
multi-force member
– Frames are designed to support loads
– Machines are designed to transmit and modify loads
• Just like trusses, frames and machines need to
be disassembled to determine member forces
– Need to draw a FBD for each member
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D
Disassembly Exposes
Internal Forces
E
C
B
W
• First, reactions of entire structure
A
• Second, disassemble and solve for
internal forces
D
Cx
Cy
E
T
C
Cx
T
Cy
FBE
A
Ax
Ax
Ay
ME221
FBE
Ay
Lecture 33
W
FBE
W
B
FBE
FBE is a
two force
member
6
Notes on Previous Problem
• Without recognizing BE is a two force
member the problem, is not tractable.
• MUST draw a FBD for entire structure and
each disassembled part
• Each FBD may have three unknown forces
which are found from SFx = 0; SFy = 0;
SMz = 0
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General Procedure
• Draw FBD for entire structure and solve for
reaction forces: SFx = 0; SFy = 0; SMz = 0
• Disassemble into component parts
– Recognize two force members
– Draw FBD and solve for reaction forces - using
SFx = 0; SFy = 0; SMz = 0
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Example Problem
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