Frames and Machines...• Draw a Free Body Diagram (FBD) of the entire structure isolated from its...
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Frames and Machines Steven Vukazich San Jose State University
Transcript of Frames and Machines...• Draw a Free Body Diagram (FBD) of the entire structure isolated from its...
Frames and Machines StevenVukazich
SanJoseStateUniversity
Frames and Machines
Frame
Machine
Frames versus Machines
A
B
C
D
E
F
G
P
PQ
Q
Frame Machine
C
DB
A
Frames and Machines• Usually contain
multiple “pieces”;• Contain at least one
multi-force member;• May contain two-force
members;• Method of analysis is
similar.
Machine• Input force (P) and
Output force (Q)• Usually held in
equilibrium
Frame• Usually unstable
without supports• Usually subjected to
multiple loads
P1
P2
• DrawaFreeBodyDiagram(FBD)oftheentirestructureisolatedfromitssupportsandapplyequationsofequilibrium(usuallythisstepisnotrequiredformachines);
• DrawaFreeBodyDiagram(FBD)ofeachpieceofthestructure;– Identifypiecesthataretwo-forcemembers,– Whenseparatingpieces,forcesatconnectionsareequalandoppositeoneach
piece,– Showallknownsupportreactionsfromthepreviousstep.
• ApplyEquationsofEquilibriumtoeachpieceandsolveforallunknownforces;– Usuallythereisonepiecethatiseasiesttostarttheanalysis,– Analyzethenextpieceandshowallknownforcesfoundfromtheprevious
analyses,– Repeatthisstepuntilallunknownforcesarefound,– Ifthelastpieceisnotinequilibrium,mostlikelytherewasanerrormadeinthe
precedinganalyses.
General Procedure for the Analysis of Frames and Machines
FBDs of Members Cut at Internal Pin Connections
Notes• Equal and opposite internal forces
at pin;• External load is applied to
member with connecting pin (can choose either member).
PConnectingpin
Frame member 2
Frame member 1
External load to joint
Internal forces (later)
PJoint A
AxAyAx
Ay
PAx AyAx
Ay
Frame member 1plus connecting pin
Frame member 2plus connecting pin
Frame member 2Frame
member 1
