# Critical Thinking in

Urban and Civil

Nov 26, 2013 (4 years and 5 months ago)

97 views

Enhancing Thinking Skills in Science
Context Lesson 6

Critical Thinking in
Engineering Process

Introduction to the different types of bridges

beam bridge

suspension bridge

arch bridge

Why are there different types of bridges?

The major difference between the three types of
bridges is the distance that they can cover in a
single span. Span is the difference between two
supports. Each of the different types of bridges
holds weight in different ways.

Beam Bridge

A beam bridge is basically a rigid horizontal
structure that rest on two supports, one located at
each end of the bridge as shown in Figure (a). A
simple beam bridge is flat across and supported by
two ends.

What happens to the bridge when a load
is put on the bridge?

When the load pushes down on the beam the
top edge is pushed together or compressed,
while the bottom of the beam is stretched or is
under tension.

What factor(s) should you consider when
you build a beam bridge?

The beam must be strong enough so that it can
support its own weight together with the added
weight of the traffic crossing it.

Arch Bridge

An arch bridge is composed of a
curved structure with abutments on
each end.

What happens to the bridge when a
load is put on the bridge?

The weight of the load is carried outward along
the curve of the arch to the abutments at each
end of the arch. The abutments also keep the
end of the bridge from spreading outward.

What factor(s) should you consider when
you build an arch bridge?

The arch bridge is always under compression
because the weight of the deck is pushed outward
along the curve of the arch towards the abutments.
The rise in the form of the curved arch causes the
vertical load to have a horizontal thrust.

Suspension Bridge

The suspension bridge literally suspends the
roadbed from huge cables, which extends from one
end of the bridge to the other. The cables are
attached to two tall towers and are secured at each
end by anchorages
.

What happens to the bridge when a load
is put on the bridge?

The cable carries the weight on a suspended bridge
to the anchorages that are imbedded in solid rock
or massive concrete blocks. The cables are spread
over a large area in order to evenly distribute the
load inside the anchorages to prevent the cables
from breaking free.

What factor(s) should you consider
when you build a suspension bridge?

The anchorages help to stabilise the bridge.
Therefore, the tower must be embedded to the
earth firmly. In such a way, the cables transfer the
forces to the towers which carry the forces directly
into the earth where they are firmly imbedded.

Scenario

The class is divided into groups of 4 or 5. You are
required to design and build a bridge made of
drinking straws. The bridge will cross a gap of
50cm. The width of the bridge must not be less
than 20cm. The total mass of the bridge must not
exceed 50 g. The strength of the bridges would
be tested by hanging loads from the middle of the
bridges.

Activity 1

Draft a design

Activity 1

Now, you have 10 minutes to discuss
with your group members to design the
bridge. Draft the steps you come across.
Also, sketch a picture of the bridge you
intend to build.

Activity 2

Introduction to the steps suggested
by Isidro
-
Cloudas and Cassis,
Glenn in engineering process

Activity 2

The steps involved in Engineering Process are
written on 6 cardboards. You are required to design
a bridge. Arrange the cardboards in correct order.
Try to answer the following questions.

Activity 2

Question:

What is the sequence of Engineering
Process to design the bridge?

Activity 2

Identify the Problem

Determine the Constraints

Brainstorm the preliminary design and
choose the best design

Analysis of Design

Design Refinement

Implementation Plan

Activity 2

Question:

What is/are the task(s) performed in
each step of Engineering Process?

Activity 2

Identify the Problem

Before you start, the problem or task that is
going to be undertaken must be known.

Activity 2

Determine the Constraints

Constraints are the limitations that must be
considered before you begin designing your
bridge.

Activity 2

Brainstorm the preliminary design and choose the
best design

Once both the problem(s) or task have been
determined and the constraints have been identified,
the group needs to think of as many ways as possible
to solve the problem. Even though all of the ideas may
not be good ones, they may inspire another idea that
may lead to a solution to the problem(s).

Once all reasonable ideas are listed and the sketches
are drawn, the group should choose the best two or
three ideas for further development. The rough
sketches should be converted to scaled or measured
drawings.

Activity 2

Analysis of Design

The designs are studied based on their merit
in relationship to strength, cost, market
appeal, and manufacturability. A decision
should be made at this point on which design
to use or rather to begin a new design.

Activity 2

Design Refinement

Each design team should attempt to rectify
the problems by making improvements in the
design.

Activity 2

Implementation Plan

Once the final design has been approved, it
must be translated from an idea on paper to
the real thing.

Activity 3

Redesign the bridge

Activity 3

According to steps of Engineering
Process, draw a completed design of
the bridge you intend to build. THREE
spatial views of the bridge should be
included. You may consider the
materials provided and the following
rubrics to draw the diagram:

Activity 3

Materials provided

80 drinking straws, 1 sticky tape, 10
paper clips, 1 pair of scissors, 1 roll of
strings, some A4 papers.

Activity 3

Points can be earned by the following rules.

The drawing is neat and legible.

The three spatial views are labelled.

The bridge span is at least 30 cm long.

The roadbed is at least 5 cm wide.

The distance between the bridge supports
is at least 10 cm apart.

Activity 3

Question:

Compare the steps you drafted with
the Engineering Process. Discuss
among yourselves which steps you
need to reconsider.

Activity 3

Question:

What are the constraints when you
build a bridge?

Activity 3

Weight, length and width of the bridge,
materials and other requirements of
the bridge itself.

Activity 4

Bridge Building Contest

Activity 4

Build a bridge according to your
completed design. You may change
your design if there is a serious
problem in your design. You may refer
to the rubrics to build the bridge. The
strength of the bridges would be tested
by hanging loads from the middle of
the bridges until it begins to buckle.

Activity 4

At the end of this activity, you are
going to evaluate the designs of
different groups and choose

a. the most cost
-
effective design
(materials used vs strength)

b. the strongest bridge design

Activity 4

Points can be earned by the following rules.

The team adhered to the design.

The model is neatly done.

The model is built with materials supplied.

The bridge span is at least 30 cm long.

The roadbed is at least 5 cm wide.

The distance between the bridge supports is
at least 10 cm apart.

Activity 5

Professional’s judgment

Activity 5

An expert or professional is invited to
give you comments so that you know
which aspects of the bridge design
need improvements.