1. An Introduction to engineering analysis
Why Structures Fail
An Introduction to engineering analysis

2. Building a Tower Each team will design a tower made of balsa sticks
Each team will do a structural analysis of their tower to predict where it will fail
Each tower will under go ‘destructive testing’

3. The Language of Engineers
Mass
Position
Velocity
Acceleration
Force
Pressure
Stress
Deformation
System Failure

4. Mass A measure of how much matter an object is made of
Does not change with environment
Metric Unit: ?
English Unit:
Pounds (lb or lbm)
Grams (g)
Weight:
(in pounds force)
200 lbf
90 kg
200 lbm
90 kg
200 lbm
Weight:
33 lbf

5. Position Position fully defines an object’s location in space
Metric Unit:
Meters (m)
English Unit:
Feet (ft)
(X, Y, Z) = (.2 m, .5 m, .6 m)
(X, Y, Z) = (1 m, .3 m, .4 m) Y Z
(X, Y, Z) = (.5 m, .1 m, .2 m) X

6. Velocity Velocity describes the rate of change of an object’s position
30 m/s
Metric Unit:
Meters per second (m/s)
English Unit:
Feet per second (ft/s)
Includes both a magnitude and direction
30 m/s
10 m/s
Can also be expressed as a ‘vector’
(x,y) = (3 m/s, 4 m/s)
4 m/s
3 m/s

7. Acceleration
Acceleration describes the rate of change of an object’s velocity
Metric Unit:
m/s/s (m/s2)
English Unit:
ft/s2
V = 10 m/s
a = 0 m/s2
V = 10 m/s
0 sec
1 sec
2 sec
3 sec
4 sec
5 sec 0m
10m
20m
30m
40m
50m
0 sec
3 sec
1 sec
2 sec
V = 10 m/s
V = ?
16 m/s
a = 2 m/s2

8. Force
Any influence that causes an object to change speed, direction, or shape
Force = mass * acceleration
F = m*a
m = 90 kg
a = 9.81 m/s2
m*a = 883 N
Metric Unit:
Newton (N)
English Unit:
Pounds Force (lbf)
F = 500 N
a = 5 m/s2
100 kg

9. Pressure P = F / A When a force is exerted over a defined area
Pressure = Force / Area
P = F / A
Force = 500 lbf
Metric Unit:
Pascals (Pa)
English Unit:
Pounds per square inch (PSI)
24 inches
24 inches
Area = 24 in x 24 in = 576 in2
P = 500 lbs / 576 in2 = .87 PSI

10. Stress
A measure of the internal forces acting on a deformable structure
Metric Unit:
Pascals (Pa)
English Unit:
Pounds per square inch (PSI)
F = 5000 kg * 9.81 m/s2 = N
F = 883 N
20 m
20 m
20 m * 20 m = 400 m2
Stress = P = N / 400 m2 = 122 Pascals
Stress = P = 883 N / 400 m2 = 2.2 Pascals

11. Stress
Types of stresses
Tension
Compression
Shear

12. Deformation
Occurs when the stress in an object exceeds the yield strength of the material
500 kPa
Material:
Purple Block
Yield Strength:
1000 kPa
Stressed
1200 kPa
kPa = kilo-pascal
Or 1000 pascals
Deformation!

13. System Failure
Occurs when the stress in an object exceeds its ultimate strength (Compressive or Tensile)
500 PSI
Material:
Purple Block
Yield Strength:
1000 PSI
Ultimate Strength:
2000 PSI
Stressed
1200 PSI
Deformation
2500 PSI
System Failure!

14. Tower Failure
Boom!
Next Week: Where will your tower fail?