# Chap 4 Equilibrium of Rigid Bodies Fall 2020

```Chap 4
Equilibrium of Rigid Bodies
๏ฟฝ ๐น๐น๐ฆ๐ฆ = 0
๏ฟฝ ๐น๐น๐ฅ๐ฅ = 0
๏ฟฝ ๐๐0 = 0
Prof. Osama Ahmed Mohamed, Ph.D., P.E., M.ASCE
Review
• Components of force
๐๐๐๐๐๐๐๐(๐๐)
๐๐
๐๐๐๐๐๐๐๐(๐๐)
• Moment
F
d
R
๐๐๐๐๐๐๐๐(๐๐)
๐๐๐๐๐๐๐๐(๐๐)
๐๐
๐๐ = ๐น๐น๐น๐น
R
Definition:
2-force member is the one that is pinned at
both ends and there is no load on it between
the pinned ends.
I can write the three equations of
equilibrium which allow me to
calculate 3 unknowns
The number of unknown reactions is more
than three, therefore, the three equations of
equilibrium will not solve this problem.
One way to solve this
problem is to write the
tension forces in
vector form
Write the two forces in vector
form so you can identify
which component produces
โ
๐๐
Recall: ๐น๐นโ = ๐น๐น
๐๐
Ropes, cables, wires,
and rods are under
tension.
Notice that a 2Force member
doesn’t need to
be straight.
๐๐ = 450
๐๐
๐๐
Consider a Free
Body Diagram
consisting of BC
only
๐๐ = 450
100 inches
๐๐ = 450
100
๐๐
```