5
Structures
104
Video:
THE COLLAPSE OF THE TACOMA NARROWS BRIDGE
In the link to the video situated in the bottom left corner we can
see the famous case of the collapse of the structure of the Tacoma
Narrows Bridge (Washington, US, 1998), together with its causes
and the solution which was adoptetd. Students will become aware
of the importance of structures from the beginning of the unit.
In order to erect a structure successfully it is necessary to take into
account permanent loads (i.e. those which are always present on
the bridge) and variable loads from traffic and other actions such
as the effect of the wind, which was the determining factor in the
collapse of the bridge.
In order to solve the problem, a structure was adopted that was
permeable to the wind and built in such a way that could not
sway like the previous one.
CONCEPTUAL MAP
The teacher can act as a guide to the unit and show the relevant
parts of the conceptual map to students and point out what is
being covered in the class.
PRESENTATION
In the same way, it could be useful to use the presentation as an
initial overview, at the beginning of each summary or at the end to
go over the contents.
After watching the video, discuss the questions and elicit
answers:
• What kind of bridge is this?
It is a (catenary) suspension bridge.
• What different structures can you see on the bridge?
Vertical cables, and pillars or pylons.
• Why do you think they used these structures?
In order to solve problems and avoid collapse, a structure was
adopted that was permeable to the wind and built in such a way
that could not sway.
Final task
Construction of a bridge
The project or task for this unit is the design and construction of a
bridge in the Tajo de Ronda. In order to understand what this task
requires, we need to have a short introduction to the project and
to three particular aspects:
❚
What do you have to do?
It provides us with the steps we
have to follow in order to complete the project successfully.
❚
Specifications.
It explains the features the bridge we will
design and build later must have.
❚
Before you begin.
These are activities that involve dealing
with issues and calculations we need to bear in mind before we
start designing and building.
●
Recognise different structures and
why they are necessary.
●
Understand how forces act on
a body and how they affect them.
●
Distinguish types of structural
elements and learn when to use
them.
●
Explain the different conditions
of a structure and analyse their
function.
●
Identify types of stress that act
on each element in a structure.
●
Design and build a structure for
a specific purpose.
5
YOU WILL LEARN TO…
STRUCTURES
What kind of bridge is this?
What different structures can you see on the bridge?
Why do you think they used these structures?
101
5. Structures
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Think about theproject.Answer the following questions:
1.
Howwide should thebridge be?
2.
Whatwill the distance be between the supports on your scalemodel?
3.
What should theminimum length of themodel bridge be so that it is strong enough at each end?
4.
What should theminimumweight be?
5.
Whatwill the total area of thebridge’sdeck be?
6.
Calculate the load that the bridge has to support for road traffic. If the load is 20 km/m
2
, how much
weight should the bridgehold?
7.
For thepurposesof testingourmodelbridge, letus takea specific load in themiddleof thearchwhich
is equal to the total of the previous question divided by 400,000. How much weight will we have to
put on themodelbridge?
Before you begin… Answer
The spacebetween the supportsmustbe50m and cannothave anyother support inbetween as
it is located over a cliff orgorge 100m tall.
Thewidthof thebridgemustaccommodate two lanesof vehicular traffic3meach,adouble cycle
lanewith 1.5m each in each direction and a pavement forpedestriansof 3m on one side.
Theminimum clearance over the deck should be 4.5m inorder to allow forfire trucks.
Youmust build a
1:1000 scalemodelof thebridge
.
Thematerials you can use are: paper, cardboard, thread and glue.
Specifications
What
do you have to do?
1
Analyse the most important types of structures.
2
Design a bridge according to the specifications.
3
Make a group presentation and choose the best design.
4
Build the bridge.
5
Test the bridge once it is built.
6
Make a video explaining the bridge and showing the
test.
In thisunit,youaregoing todesignandbuildabridge in theRonda
Gorge to accompany the one that has existed since 1785. For this
task, there will be a class competition where everyone will present
a model of their design for the bridge.
The
PuenteNuevo
over theElTajoGorge inRonda,Malaga
Theminimum clearance is the space
allowed for things topass through
tunnels,underbridges and through
other structures
FINAL TASK
Building a bridge
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TEACHING SUGGESTIONS
