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Structures
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4.
Man-made structures
The question which students are asked here is about the different
types of bridges they can think of. With the help of everyone in
the group, you could brainstorm the oldest to the most modern
one to make them aware of the differences between one and
the other and their possible relationship to the different types of
structures.
In this section two important aspects of structures come together.
On the one hand, a classification is established. On the other hand,
this formal classification is related to the historical evolution of
structures. Also, although we are referring to building structures,
these structural types are applicable to technological objects as
well.
By starting from early history, the basic types of building structure
can be listed.
You could also mention that all the structural elements which
have appeared are still used today. Also, although their use is
less common, it is normal to come across load-bearing walls and
arches in buildings these days.
Before beginning to explain the types of structures, ask students
to do a drawing in their notebooks of the bridges which they can
see on the double-page spread. Also, ask them to analyse how
one of them collapsed. In this activity they can also make a sketch
or diagram of the bridge from their task designs.
4.1.
Solid structures and lintels
It is important that students notice the simplicity of very early
man-made buildings as well as the importance of stability in
the design of these primitive structures. You can also discuss the
limitations caused by the material used (parts extracted from rocks).
Also, ask what types of structure could be built from sand on the
beach and which could not.
In the photo of the stone bridge, students can try to find out what
would happen to if load of a weight corresponding to a person
situated in the centre of the bridge is taken across the structure.
This can be used as a preparatory exercise for any work on
framework structures. This activity can also be used with any loads
and structures that feature in the unit.
4.2.
Vaulted structures
As regards these types of structure, if time permits, you can teach
students using slides with pictures of different vaults and arches
which have been built in different eras.
One of the advantages that arches have is that the greater the
load placed on them, the more securely their parts fit together.
They can be broken by lateral forces which are produced at the
level of the lower lateral arch stones if they are not counteracted
by a greater load which centres these forces.
4.3.
Triangular structures
Triangular structures made of wood go back a long way in history.
They were already in use during the Middle Ages (mainly for roof
trusses). Their advantages compared to other types of structure
are their lightness and the fact that they require a small amount
of material.
Their weak points are the joints, whichmust resist traction stresses.
For the calculation of forces these joints must never be considered
rigid but as if they formed free joints – hence the importance of
the triangular shape.
When the first foundries appeared, the use of triangular metal
structures became more common. It was the era when pavillions
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5. Structures
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Understand
13.
Look at the photos.
a)
What kind of stress do the stones in the pyramid support? And the
columns of the bridge?
b)
What is the purpose of the spaces between the lintels? Do they
support stress?
4.
MAN-MADE STRUCTURES
Over time, human beings have become better at building structures. We know
more about them and we have lighter and stronger materials.
4.1.
Massive structures and lintels
The first man-made structures were carved from rock or were built by
stacking
13
rocks or other materials. This left little space between them, like in the Mayan or
Egyptian pyramids.
Short stoneorwooden
lintels
14
werealsoused tomakewindowsandopen spaces,
for example, in Greek temples.
4.3.
Triangular structures
These structures are made from bars, normally metal or wooden. The use of
triangular shapes means they are not easily deformed. This makes them ideal
for building bridges (triangular beams), covered with large
trusses
15
and vertical
structures, like towers and
scaffolds
16
.
13
stack
:
a group or pile of material
placed one on topof another
14
lintel
:ahorizontal supportacross the
top of two verticalposts or columns
Apply
14.
Find different types of arches
in vaulted structures on the
Internet and in books about
art and architecture and draw
them. Illustrate the different
types of stress they experience.
What kinds are they?
Understand
17.
Look at the bridges and explain how they transfer loads through the
various structuralelementswhichyou can see in thephotos.Forbridges
of the same length, which bridge would have thicker cables? Why?
Analyse
15.
Identify what material was used to build the
Eiffel Tower. Find out which material we use
nowadays for thesekindof structuresand list
the advantages.
Ribbedvaultsandpointed arches
Suspensionbridge
Railwaybridgesuse theheightof the truss so that the
trains can cross them
TheEiffelTower.
Thiswas the
tallest structure in theworld
formany years
Bridgewith round arches
Cable-stayedbridge
Amassive structure
Lintels
4.4.
Suspended structures
This type of structure uses cables, called
suspenders
which the structure hangs
from. When they can be adjusted, they are called
tension members
.
The cables only bear traction stress, but the advantage is that they can adapt
their shape to different loads at different times and they are incredibly light.
Cables are used to fasten bridges,
marquees
17
, antennas and towers.
There are many kinds of suspended structures which can cover large spaces like
stadiums and pavilions, without the need for columns or pillars.
15
truss
:
a framework of posts and
beams
16
scaffolds
:astructureforconstruction
workers on the outside of a building
Analyse
16.
Look at the different
types of trusses. Which
ones would be better
for a bridge? And for a
roof? Give reasons for
your answers.
queenpost truss
Pratt truss
Howe truss
Warren truss
queenpost truss
Pratt truss
Howe truss
Warren truss
trussheight
catenary
suspender
suspender
4.2.
Vaulted structures
With arches and vaults, builders could cover larger spaces and have bigger gaps in
the structures.
Vaulted structures
are formed by arches and vaults using stones that are cut
in such a way that the only stress they support is compression – no problem for
hard stone.
The Romans used round arches to build bridges and aqueducts and they used
barrel vaults and domes to cover basilicas and pantheons. Later, pointed arches
and ribbed vaults were used in mosques and cathedrals. We still use them today.
17
marquee
:
a very large tent
