Bridges
–
Quiz Review
Quiz is Friday,
September 12
No need for calculators
Design Process
Describe the problem
Describe the results you want
Research, gather information
Define the constraints
Propose solutions by sketches
Build prototype
Design Process (cont)
Understand how our bridge building project
used the design process.
How is the
engineering design process
different than the one we used?
Iterative design
means many repetitive
efforts (as if we rebuilt the bridge several
times in order to improve its performance)
Types of Forces
Tension
Compression
Torque (or twisting)
Sheer (two forces in opposite directions)
Bending (opposite of beam loading)
Beam loading
And why do we care????
Be able to tell why engineers, designers,
manufacturers and constructors care about strengths
of materials….
Materials can become stronger if they are under
tension or compression (think about DIA and its roof)
When
nanotubes
are combined with polymers they
form super

strong
composites
, making projects like
the space elevator closer to reality.
How triangles react to loads
How do you account for small variations in the colors?
Types of Loads on Bridges
The weight of the structure itself
1.
Vehicles
2.
Soil adds a load because of
hydrostatic pressure
3.
Thermal load (heats up and cools down)
4.
Earthquake load
5.
Wind, snow, ice
Types of bridges do you need to know
Beam Bridge
–
How would your strengthen a simple beam bridge?
–
Why does that work?
Truss Bridge
–
How are these an improvement to beam bridges?
Suspension Bridge
When are these used? How do they work?
–
What part of a suspension bridge supports most of the weight
Arch Bridge
Why do they work? Is it due to compression or tension?
http://science.howstuffworks.com/bridge2.htm
Use this website to find answers
Terminology
When any structure breaks because of too much load, it
fails.
When a structure is under too much compression, it
buckles
When a structure is under too much tension, it
snaps
The length of a bridge is called the
span.
Know these types of connections we used:
Butt joint
Lap joint
Mitre joint
Drawing types you need to know:
Orthographic
Isometric
Perspective
Oblique
As

builts
Isometrics
These are used in engineering drawings because
they are easy to take measurements off of
They are easy to recognize because they have
120
degree angles in them
They do not account for distance like your eye or a
camera view would
Drawing Types
The figures on the left are
orthographic, or 2D
The figure on the right is an
isometric
What type of drawing?
This is
isometric
; the corner of the truck bed is at 120 degrees to
horizontal
What type of drawing?
This is a floor plan of a
bathroom.
It is really a “birds eye” view
It is 2D…
It is orthographic in nature
What type of drawing?
This is a diagram of how to
install drainage and venting in a
bathroom
Notice the angle of the pipes
that are on the ground.
They are at 120 degrees to
horizontal, therefore its
isometric
What type of drawing?
These are figures from a safety
manual for workers in a shipping
business
What type of drawing?
What types of drawing?
Notice how the perspective drawing shows lines converging, even
though they are parallel in real life.
Oblique drawings are useful, but are not true size, like isometric
drawings
Converging lines
True in the front, but
can’t measure the
length off this drawing.
Notice the 45 degree
note!
These are isometric
Figure on the right has circular parts, but look at the square
piece; it has a corner that is at 120 degrees to horizontal
What drawing type?
This is
oblique
(45 degrees to
horizontal)
These are
orthographic
; they are 2D
These are called
elevations
What drawing type?
This is a simple roof plan.
The roof slopes, but this is still
considered a 2D, and an
orthographic
projection or drawing.
Examples of Perspective Drawings,
Paintings
Measuring material strength
This is a UTM, or a Universal Testing Machine. There are common, and
would be found in many labs that test concrete, steel, etc.
Making sample concrete cylinders for
testing in the lab.
Nanotubes = hexagonal structure
A carbon nanotube has an extremely high
strength to weight ratio.
Carbon
nanotubes
are smaller than the eye
can see, yet stronger than steel
Measuring the strength of a
material….the MATH!
Bridge weight
Weight of load
at failure
Convert ounces
to pounds
Strength to
weight ratio
8 ounces
(.5 pounds)
80 pounds
4 ounces
200 pounds
16 ounces
158 pounds
Calculate these strength to weight ratios without using a calculator.
Which is the strongest bridge?
Measuring the strength of a
material….the MATH!
Bridge
weight
Weight of
load at
failure
Convert
ounces to
pounds
Strength to
weight ratio
8 ounces
(.5 pounds)
80 pounds
8 oz = .5
pounds
80/.5=40 so
S/W =
160
4 ounces
200 pounds
4 oz = .25
pounds
200/.25 =
800
16 ounces
158 pounds
16 oz = 1
pound
158/1=
158
The 4 ounce bridge is the strongest, express as
1:160
Struggling with the math?
If you struggle with division like 80 divided by .5…..
then convert the decimal to a fraction.
80
÷
.5
is the same as 80
÷
½
Invert that second fraction and multiply
Now you have 80 x 2, right? Because ½ inverted is 2/1, or 2
80/1 x 2/1
Multiply the tops
Multiply the bottoms
Now you have 160/1 or just plain old 160!
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