Theory for the structures unit, 3 ESO bilingual program

1. Unit 4
DEPARTMENT OF TECHNOLOGIES 3rd ESO

2. INDEX

4. What is a load?
Natural and artificial structures are created to support
loads. Loads are forces that can deform a body or make
it move.
Types of loads:
-Fixed Loads: They always have the same value.
-Variable loads: Those that can change as time passes or
due to natural disasters.
What are the loads that
the human body can be
subjected to?

5. Fixed loads:
- Weight of walls
- Weight of the roof
- Weight of the floor slabs Variable loads:
-Weight of people
-Weight of the furniture
-Weight of the snow
-Wind pressure
-Water pressure/weight
Fixed load:
-Earth pressure
Variable load:
-Earthquake loads
Fixed loads on
basements
-Weight of gardens
Typical loads acting on a building’s structure

6. Is gravity a force?

7. Functions of the structures
Supporting loads
Resisting external
forces
Providing shape
Protecting the
inside
Do you think one structure can do more than one
function at a time? Think of an example.

8. Functions of the structures (II)
Supporting the weight of
elements that lay on
them.
Example: the pillars (columns) hold the
weight of the beams. The beams
support the weight of floor slabs.
Resisting external
forces like the wind
pressure, the vibration
caused by traffic, the
impact of waves…
Example: the walls of a dam that holds
water.

9. Providing shape to an
object, machine or
construction.
Examples: the metal frame of a tent
gives shape to a textile. The
fuselage of an airplane wing.
Protecting the internal
elements of an object,
building or machine.
Example: the
outer case of a
vacuum cleaner
protects the
internal pieces
and circuits.
Functions of the structures (III)

10. Definition of structure
A structure is a set of elements in a body that
are intended to resist the effects of the forces
that act on it.
A structure prevents a body from breaking or
becoming too deformed.

12. Types of structures
Natural Manufactured

13. Types of structures
Structures of machines and
objects:
- Laminar or case structures
- Frame structure
--E
Construction structure:
- Massive - Lattice
- Triangulated - Suspended
- Pneumatic - Shell

14. Structures of machines and objects
Laminar or shell
structures: formed by
thin resistant sheets.
Examples: video game controller
case, car’s bodywork, hull of a
boat…
Frame structures:
formed by bars, tubes or
strips united to form an
skeleton.
Examples: a bicycle frame, a ladder, an
umbrella, a chair…

15. Structures of constructions (I)
Massive structures:
Heavy resistant
structures built by
stacking rock or
other materials.
Examples: walls of dams,
pyramids in Egypt, ancient
temples…
Lintelled structures: To
create windows and
open spaces, wooden or
stone lintels are used.
Vaulted structures: The
arch is a self-supporting
element that can resist
compression without
mortar or cement.
A vault is a series of
arches placed side by
side with the spaces
between them filled in.

16. Structures of constructions (II)
Triangulated structures:
Made from metal of wood
bars articulated into
triangles. They are very
light and can cover large
spans.
Examples:
electrical
tower,
sports
center roofs,
bridges…
Suspended structures:
Formed by cables (called
tie rods) connected to
supports from which the
structure hangs.
Examples: suspension bridges,
stadiums…

17. Lattice structures: Built
by steel or reinforced
concrete bars joined
to form a rigid grid.
Example: the structure or a normal
housing building.
Structures of constructions (III)
Footings
Prevents the pillars
from sinking into the
ground
or Pillar

18. Structures of constructions (IV)
Pneumatic structures:
They are supported by
compressed air that
stretches a plastic
surface to create
enclosed spaces.
Examples: funfair attractions, field
hospitals…
Shell structures: Built by
a three-dimensional
curved plate whose
thickness is small
compared to the rest of
the dimensions.
Example: roofs of large buildings.

20. What are the efforts?
The efforts are the internal answer of a
structure to the presence of loads.
Try to understand: What happens when
I’m lifting a weight (load) and someone
adds more weight?
My arm needs to make a bigger effort,
as a response to the variation in the
load.

21. Types of efforts
TRACTION or
TENSION
COMPRESSION
SHEAR
BENDING
TORSION

22. Types of efforts(I)
TRACTION or TENSION
Effort to which an object is
subjected when the forces
that act on it tend to lengthen
it.
COMPRESSION
Effort to which an object is
subjected when the forces
that act on it tend to shrink it.
Tie rods in suspended
structures are
subjected to traction.
Pillars and arches
support vertical loads,
so they tend to shrink.
They are subjected to
compression.

23. Types of efforts (II)
BENDING
Effort to which an object is
subjected when the forces
that act on it tend to bend
it.
TORSION
Effort to which an object is
subjected when the forces
that act on it tend to twist it.
Both the central beam in
a bridge and the pole
support loads that tend
to bend them, so they
are subjected to
bending.
The axles of two
friction wheels are
subjected to
torsion when the
wheels are turning.
In this strange
tower, each cable
pulls the pillars in
one direction. The
pillars will thus be
subjected to
torsion.

24. Types of efforts (III)
SHEAR or CUTTING
Effort to which an object is
subjected when the forces that act
on it tend to cut it. It happens
when two opposed forces act very
close to one another.
In cutting tools, each blade
exerts a force in opposite
directions. The paper is
subjected to shear.
A screw on the wall supports
the load hanging from it an the
vertical reaction of the wall in a
small pieces of material. It’s
subjected to shear.

25. Think to analyse…
These are the main elements in a
suspension bridge. What efforts affect to
each part?
Board / Beam
Tie rods
Tower
Pillar

27. Basic elements (I)
Foundations
Massive elements
placed undergroun
that support
compression efforts.
Tie beam
Thin bars that
support tension or
compression.
Walls
Massive elements
that support
compression efforts.
Beams
Horizontal elements that
support bending in the
center and shear in the
extremities.
Pillars
Slim elements that
support
compression efforts.

28. Basic elements (II)
Walls
Massive elements
that support
compression efforts.
Arches
Curved elements
that tranfer the loads
the hold to the
supports on their
extremities.
They are subjected
to compression.

30. What is the resistance of a structure?
Resistance is the capability of a structure to
support loads without breaking or
deforming excessively.
To design a structure, you must take into
account the efforts that will act on it. Do
you remember the 5 types of efforts?
There are two factors that determine the
resistance of a structure:
a) The materials it’s made of.
b) Its shape.

31. Materials
When we know the efforts that will act on a
structure, we choose the best materials to
support them.
WOOD
STEEL
BENDING
TRACTION
resist
MINERALS COMPRESSION
resist
they combine
and form
COMPRESSION
BENDING
TRACTION
REINFORCED
CONCRETE
resists
WOOD
PLASTICS
ALUMINUM
resist
SMALLER
EFFORT
than steel, minerals,
concrete and wood

32. Reinforced concrete (I)
Invented at the end of the XIXth century,
reinforced concrete changed architecture
and construction deeply.

33. The shape
The same material can resist efforts better
or worse depending on the shape we
provide to it.

34. The shape (II)
With the objective of resisting different
types and intensities of efforts, steel is
industrially shaped into different types of
profiles.
Every profile
has a different
resistance to
the different
types of efforts,
due to its
shape.

35. Rigidity and stability
Apart from being resistant, a structure
need to be rigid and stable.
Stability  Capability to stand up right
under the presence of loads, without
sliding or falling down.
Rigidity  Capability to avoid excessive
deformation under the presence of loads.

36. How to achieve rigidity? (I)
Rigidity depends on the right position of every
elements and in the joints between elements.
JOINTS
Rigid joints (welding,
adhesives…) don’t
allow pieces to
move or split appart.
Welding is used in
metallic lattice
structures to
connect pillars and
beams.
.

37. How to achieve rigidity? (II)
TRIANGULATION
In metallic structures
where joints are made
with nuts and bolts,
the resulting joints are
articulated, so they
allow for movement.
To prevent the
structure from
deforming, diagonal
bars are used to form
triangles.

38. What does stability depend on?
The stability of an object depends on the position
of its center of gravity, which is normally in the
center of the geometrica figure.
An object is stable if its center of gravity is on top
of its base.
Stable object
Unstable object

39. How to achieve stability? (I)
INCREASING THE SIZE OF
THE BASE
This way, the center of
gravity will be on top of
the base.
INCREASING THE
WEIGHT OF THE
BASE
This way, the center of
gravity moves downwards
and it’s more difficult for
the structure to overturn.
In cranes, a big load is
added to the base with
this objective.

40. How to increase the stability? (II)
USING ANCHORING
SYSTEMS
Embedding the structure
in the ground or using
tie rods can increase its
stability.

41. The end