Statics Case

Characteristics:

a) all external loads are at joints

b) all members are straight, 2F members

c) all joints are treated as "pin" connections (no moment)

d) all forces in members are axial (T or C)

Analysis:

a) method of joints:

Simple Truss ONLY

#mems=#joints-3

use particle statics-concurrent force system at every joint--therefore, 2 force equilibrium eqns/joint

i) FBD of each joint with unknown forces shown as arrows in Tension

ii) must start at joint w/ 2 unk

b) method of sections

FRAMES

-->Characteristics:

a) external forces can be anywhere on the members

b) members can be bent

c) members can be "continuous" therefore can be 2F or MF

d) "rigid" frame usually has 3 reactions at supports

e) "non-rigid" frame usually has 4 reactions at supports

-->Analysis:

a) RIGID FRAME:

* solve rxns first if nec

* take mems apart & check for stat determ (#equns=#unk)

* solve intern forces by using FBD of MF mems and 3 equil equns/MF mem

* number of intern forces at joints depends on the typed of mems connected there: MF to MF or MF to 2F

* applied forces at joints must be placed on MF member only; if joint is MF to MF, then the applied load may be placed on either one of the MF members, but NOT both

b) NON-RIGID FRAME:

* solve for as many rxns as can be found w/ whole frame together

* FBD of MF members and 3 equil equns/MF member; check for stat determ

* solve for required forces

MACHINES

-->Characteristics:

a) all are "non-rigid"

b) made up of MF and 2F members

c) applied forces are considered the "input" force

rxn forces are considered the "output"