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Unit 5. Forces and structures (Forces (What a force can do? (Stop a moving…
Unit 5. Forces and structures
Types of structures
4.1. Mass structures
(f.e. Egyptian pyramids)
4.2. Framed structures
(f.e. a ladder)
4.3. Laminated structures
(f.e. sheets of metal that cover a car)
4.4. Hanging or suspended structures
(f.e. bridges)
4.5. Triangulated structures
(f.e. cranes)
4.6. Vaulted structures
Arches
(f.e. Roman Arch)
Vaults and domes
Vault
(f.e. Seville Cathedral)
Dome
(f.e. Florence Cathedral Dome)
4.7. Structure failure
Material fatigue
Rusting and corrosion
Incorrect structural design
Profiles and structures
6.1. Profiles
Open profiles
I, H or double T profile
T profile
L profile
U profile
Closed profiles
Rectangular cross section
Square cross section
Round cross section
Triangular cross section
Commercial shapes usually made out of steel, aluminium or other materials capable of resisting different types of stresses
6.2. Trusses
Joined profiles and bars together using brackets forming triangular shapes
Main advantage: very light in comparison to the weight they can support
To create volume, trusses are joined using bars and beams
6.3. Types of trusses
for covers and roofs
Fink
Fan
King Post
Howe
Scissor
Pratt
for bridges
Pratt
Warren
Browstring
Structural components
Foundations
Transfer structural loads into the ground
Arches
Curved frames distributed between the elements subjected to compression
Braces
Steel cables to provide rigidity and resistance subjected to tensile stresses
Beams
Horizontal elements that support the load between two support points, mainly subjected to bending stresses
Pillars and columns
Vertical elements in a structure, mainly subjected to compression stresses
Forces
1.3. Center of gravity
Representative point in a body, where all its mass is thouhgt to be concentrated. It's a geometric point
1.4. How we measure forces
Many different kind of tools. For example
weighing scales
dynamometers
based on how far a spring can strech in propotion to the force applied to it
Units
Forces (Newton (N))
Mass (Kilogram (Kg))
1.2. Load and forces
An object has certain weight,which is counterbalanced by the element supporting it, with an equal forcen in opposite direction
Kinds of loads
Dinamic or live loads (f.e. weight of snow on roofs)
Environmetal loads (f.e. earthquakes)
Static or dead loads (f.e. weight of a structure)
1.5. Types of forces and loads
Depending on magnitude and length over time
Fixed
(f.e. weight of a building on the ground)
Variable
(f.e. load supported by a bridge when vehicles drive over it)
Depending on how they are applied
Specific or concertated
(f.e. hammer hitting the head of a nail)
Distributed
(f.e. snow that has accumulated on a roof)
1.1.Balanced forces
Several types. For example
Inertial forces (f.e. force a shotgun applies to a bullet)
Gravitational forces
(force of attraction the Earth exerts on everything on its surface)
All the forces acting on a body must equal zero in order for it to be balanced.Otherwise,the body will move
What a force can do?
Stop a moving body
Change the shape of a body
Move a starionary object
characterised by
value or intensity
direction
represented by arrows
Lenght tells us its magnitude
Point in a certain direction and have a specific meaning
Stresses
Bending
(f.e. we stand on a board that is supported at its ends)
Torsion
(f.e. wiring a wet cloth)
Compression
(f.e. how legs of a chair are affected when we sit on it)
Shearing
(f.e. cut something with scissors)
Tensile
(f.e. pull a rope from both ends)
Structures
3.2. Copying nature
The key lies in the correct distribution of forces and weights exerted
Natural structures
Result of the geological evolution
(f.e. caves in the Cappadocia region of Turkey)
Provided by animal kingdom
(f.e. dams built by beavers)
Mimicking natural structures
(examples)
Air conditioning system based on how termites naturally oxygenate their termite mounds
Supply water directly from external surfaces of buildings like the structure of some plants,such as lotus, collects humidity on their surface
3.1. What do you think a structure is?
Its purpouse is to support forces, weights and, in general, any type of load
Internal stresses appear in the components of a structure when loads are applied to it
They must be desinged so that their shape and size remain unchanged
Element or group of elements joined and coulpled together
3.3. Structures throughout history
Stone and wood for building
(f.e. Egyptian pyramids)
Constantly evolving structure building techniques
(f.e. manual hoists for building large European cathedrals in the Middle Ages)
(19th century) Iron and steel
(f.e. modern skycrapers)
(Today) Reinforced aluminium,plastics and composites
Structures are designed according to three essential conditions
They must be able to support themselves without becoming deformed
They must be resistant to both external loads and loads produced by their own weight
They must be stable