structures

Structures(technoloystudent)
Structure
Support a load and its own weight
Support to hold an object upright and steady
Reach across a gap
Span a distance
Contain something
Protect something
Transporting
Sheltering
Lifting
Fastening
Types of structures
Natural structures: Not made by people
Man-made or manufactured structures: Built by people

man-made structures

Massive or mass structures
Piling up materials
Held in place by its own weight
Solid or layered
Pyramids,dam
Post-lintels system
No rigid connection between the lintel and posts
The only stress they support is compression
Horizontal load acts as a single cantilevered beam
Masonry structures
Stone,brick bonding together with mortar
In muli-storey buildings all Load-bearing walls must be one on the top of the other
Frame structures
Have a skeleton of strong materials:wood,steel,reinforced concrete
These materials must be strong in both tension and compression
Vaulted structures
Arches,vaults,domes
Bridges,aqueducts,cathedrals
Triangular structures
Truss of Roofs and Bridges, Pylons of High Voltage
They are made of bars to form triangular shapes
Suspended structures
Bridges,marquees,antennas or aerial,towers,stadiums,pavilions
They use cables(suspenders)
Shell structures or Laminated structures
laminates of metal,plastic or composite material
curved shape and folds
They use very little material(thin outside layer)
Turtle shell,food cans,egg cartons,bottles Igloos
Pneumatic structures
Spatial and geodesic

Trusses and Frames

Truss

External forces will be resisted by member's axial capacity only (tension and compression)
Supports can be assigned as hinged or roller (not fixed)
Members can only undergo translational deformations ( not rotation)
Structure typically made of straight members conected at joints (nodes)
They behaves as a single object
They are typically composed of triangles
A Triangle is the simplest geometric figure that will not change shape
A tetrahedron shape is the simplest space truss

Frame

The members are connected rigidly at joints
Self-weight of the frame is considerable compare to the load
Individual members can carry transverse load
The load can pint load, uniformly distributed or uniformly varying load and moments can be applied at nodes or anywhere along the length

Structural conditions for a structure to work well

Resistance
The capacity to bear tensions without breaking
It depends on:
Rigidity or stiffness
The capacity to resist deformation or become deformed but fulfil its function
It comes from:
Stability
The capacity to remain upright and not tip over(fall over)
It depends on:
Center of Gravity ( C.o.G. or C.G or G.)
Equilibrium (Stability)
It is a measure of the body's ability to maintain its original position
*center(AmE) = centre(BrE)

Effects of Forces on a body

Acceleration(Newton's Law: F = m · a)
Change state of rest or movement -speed up or slow down, start or stop-
Change direction of the force
Deformation -change the shape- (Hooke's Law:F=k ·x)

Stress/Strain curve

Stress
the force that changes material and its shape and volume
Strain
deformation:the change in the material such as its shape and size
Elastic strain
If the stress is removed the original size or shape will be restored
Brittle deformation:breaks while undergoing elastic strain
Plastic strain
If the stress is removed,the original size or shape will not be restored
dultile deformation

Types of loads acting on structures(external forces)

Static(stationary):weight of the structure
Dynamic(moving):people,vehicles,wind,snow,waves

Types of Stress(internal forces)

Forces(technoloystudent)
Tension or tensile stress
stress that pulls on material making it thinner in the middle until it breaks
Compression or compressive stress
stress that squeezes(shortening)material making it thicker until it breaks or bends
Bending or flexural stress
stress that stretched and squashed at the same time. Combination stress:Tension,compression and shearing
Shear stress or shearing
stress that pushes material in opposive directions(sliding)making it to break(cut)or change its shape
Torsion stress
stress that twist or turn a material
Buckling
It is a stress that combines both bending and compression

Other stresses

Fatigue stress
If a material is subjected to repeated stress
Resonance
vibration that coincided with that of the structure

Structural elements or members in a structure

Vertical elements

Pillars
Support the weight of the structure on top
Transfer the weight to a lower level
Transfer the weight to the foundations
rectangular or circular
It is structural
They are subjected to compression and buckling
columns
circular(round)pillar
decorative or structural function
pilaster
upright support member projecting slightly from the face of a wall(attached to,part of the wall)
pier
A vertical support
for adjacent ends of two bridge spans-caissons-
for large building-cylindrical-
they will support a greater load than a pile

Linear horizontal elements

beams
keep a space between two supports
Sit on pillars
transfer the weight of the slabs or the roof
They are supported at one end only(cantilever)or supported at both ends
Support at one end only(cantilever):load at the top,top is in tension and the bottom is in compression
Support at both ends:load at the top,top is in compression and the bottom is in tension
Form of the beam:simply solid or hollow or special cross-sections
They are subjected to bending-shearing and torsion-
Joists
Small beams within slabs
Carry the load to the beams
Girders
Main horizontal support which supports smaller beams
I-beam cross section or box shape or Z shape...
Lintels
Create open spaces between pillars for windows or doors in walls

Curved elements

arch
Cover the space between two walls or pillars
Resist compression stress
It is self-supporting
It requires no mortar or cement
vault
It is built by using a series of arches(barrel vault,groin vault)
It is built by intersecting arches(rib vault,net vault,fan vault)
dome
semi spherical roof-arches at an angle

Elements to hold up the loads or arches and vaults

buttress
subjected to lateral loads
Reinforce the wall
Transfer the loads from the vaults to the ground
flying buttress
It is an exterior arch
subjected to lateral loads
Transfer the loads from the vaults to the buttresses

Vertical elements that transfer loads to the ground

Load-bearing walls
They bear compression stress
Retaining walls
They bear bending stress

Concrete slabs

They resist bending stress
They transfer the loads of the rest of the structure
Joists
Carry the weight to the beams
Blocks
Fills the space between the joists
Hollow elements that help to make the slabs lighter
Reinforced concrete surface

Foundations*

Distribute the load of the structure and self-weight so that it does not sink
Most soils are self supporting(exception of sandy and silty-mud or clay or small rocks deposited by a river or lake-soils
Load the bearing surface at uniform rate
Prevent the lateral movement
Increase the stability

Linear elements to resist tension stress

Suspenders, tension rods, tie, brace
normaly steel cables
resist tension stress
They are used in suspended structures and in bracing

*Cables

Cable
One or more groups of wires, strands or ropes
Strand
wires laid helically about a centre
Rope
Strands laid helically around a central core
Tie
Tension member or tie member is a structural member subjected to tensile force
Built-up members or sections
Two or more members are used
Rod
structural Shape: square or round
Bar
Structural Shape: rectangular plates

*slabs

horizontal structure under the floor
joists are small beams
ceramic blocks,bricks placed between the joists
steel mesh or rebar and concrete
Triangulation
Combination of struts and ties to make triangles
Triangles make strong and rigid a structure
A four-sided structure is non-rigid
If you join two corners with a bar or member,you will get a rigid structure
you can use a triangular gusset plate

Romanesque Architecture

dark,massive buildings with small windows
solid walls
main supporting structural element of the ceiling
barrel vault or Roman vault(continuous semicircular sections)
groin vault
buttress
resist the sideways thrust of a vault

Gothic Architecture

light,less massive with more windows than walls
ribbed vaults
net vault
fan vault
pointed arches
cluster columns
flying buttress
support the lighter walls,higher ceiling and slimmer columns
towers and spires
piers with pinnacles or statues
stained glass windows
rose windows

Vaults

Vault
arched roof

types of vaults

barrel vault
semi-circular arches
they are heavy
Their height must be proportionate to their width
groin vault or double barrel vault or cross vault
intersection at right angles of two barrel vaults
rib vault
rib is a thin arch
pointed arches
two or three ribs divide into four or six sections
allow greater height
allow the filling to be thinner and lighter
net vault
fan vault

Building materials

wood
stone(only in compression)
steel
it needs a protective coat that prevents oxidation and corrosion-paint,galvanizing or alloyed with chromium and nickel-
aluminium
reinforced concrete
concrete is a material made by mixing together cement,sand,small stones and water
Reinforced concrete:concrete plus steel bars

Bridges

Elements of the bridge:
bridge deck or deck truss(bending)
abutments (compression) and anchorage (tension)
support,pier, tower, pylon (compression)
cables(tension)

Types of Bridges

Beam(up to 200 feet-60 metres-)
Arch(up to 1 000 feet-300 metres-)
Cantilever
Cable-Stayed. A Shape
Suspension. M Shape(up to 7 000 feet-2 100 metres-)
Cantilever bridge
Types:
The cantilever arms support loads by tension of the upper members and compression of the lower ones
Cable-stayed bridge
elements:
for spans longer than cantilever bridges and shorter than suspension bridges
*Abutment(like a buttress)
Substructure at the ends of a bridge span or dam or supporting one side of an arch or vault
acting as Vertical and lateral support, as well as retaining walls
*Deck
Suspension bridge
elements:
Simple suspension (or rope or swing or suspended or hanging or catenary) bridge
It has no towers
It is supported from anchors at ends
The deck follows the arc of the load-bearing cables