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Structures and Designs

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Presentation on theme: "Structures and Designs"— Presentation transcript:

1 Structures and Designs
By Mr. R. Gallagher

2 Vocabulary Thrust lines Equilibrium Elasticity
Imaginary lines of force caused by loads They are transmitted through all parts of the structure to the ground Equilibrium When a force is balanced by another force Elasticity The ability of a material to return to its original shape and size when a load is removed Some materials are so brittle that instead of changing shape they break without warning

3 History of Towers People have been constructing buildings since ancient times 4 story houses were made 4000 years ago and the Romans made 10 story buildings Towers are mostly vertical structures that support a load.

4 Constructing Towers Until modern times, structures were designed and built using the method of trial and error Each builder would build a structure higher than the last until the structure failed Modern engineers use mathematics, physics and computers to design structures High strength reinforced concrete has replaced stone, wood and brick Engineers use; computers to perform structural analysis, scale models and wind tunnels to better understand a structure’s strength

5 Types of forces on structures
Dead and live loads load – forces applied to a structure Dead loads Permanent loads that do NOT change or move The weight of the structure itself is a dead load Live loads Those that move and change Ex. Wind, melting ice, truck moving over a bridge

6 Types of forces on structures
Static and dynamic loads Static load Loads that do not change or change slowly loads that build up gradually over time, or with little dynamic effects Ex. Ice melting on a bridge Dynamic load Loads that change quickly Ex. A gust of wind

7 Stress and Strain Stress Strain
Is the amount of force placed on an object Is measured in Newton's Strain Is the distance an object deforms under stress

8 Types of Stress Compression The tendency to push or squash a material
A material under compression is always shorter

9 Types of Stress Tension The tendency of a material to be pulled apart
A material under tension is always longer

10 Types of Stress Shear Occurs when a material has two parallel but opposing compression forces One part slides past the other Ex scissors

11 Types of Stress Torsion The tendency of a material to be twisted
Ex a wrench tightening a nut

12 Types of Stress Bending Placing a load in the center of a span
The top part compresses while the bottom tenses

13 Recall Types of Stress

14 Recall Types of Stress

15 Strong Shapes Triangles compression compression tension
Are a strong shape Used in most structures When under a load one side of the triangle is always in tension which gives the shape strength Have greatest support when the force is applied to a corner not in the middle compression compression tension

16 Strong Shapes Squares/rectangles
May work well for columns but are not as strong as cylinders When placed under a load its shape will distort Making two triangles from the square will increase its strength

17 Strong Shapes Cylinders
Is a strong shape when force is applied from the ends It is strong because there aren’t any corners and the force is distributed evenly around the cylinder Strong against compression

18 Strong Shapes Arches Arches support loads anywhere along their curves unlike a triangle A disadvantage is that arcs push out at the base Therefore abutments at the sides must be used to prevent the arc from flattening abutment

19 Strong Shapes Domes Use the same principles as arcs
Are really many arcs placed together Used in stadiums so that columns do not get in the way of the playing field

20 Trusses A. Howe Truss

21 B. Pratt Truss

22 C. Warren Truss

23 Beams I Beam Shape of an “I” Very strong and economical
Used in houses, buildings and bridges Can be steel or wood

24 Beams Box Girder Are “U” shaped and reinforced
Used mainly in bridges of lighter pay load

25 Beams T beam                                                                                                                                Double “T” Beam

26 Bridges Beam Bridges Bending stress
Supported by the ends on the embankment When the span is too great columns are added for support The shapes of columns and girders make a difference in the strength of the bridge

27 Bridges Truss Bridges In 1890’s the train became popular
Bridge builders needed to strengthen their beam bridges It had to withstand massive weight and vibrations They solved this by using trusses

28 Bridges Old Arc Bridges
For 1000’s of years arc bridges were made from wedge shaped stones called voussoirs They were placed over a wooden framework The very middle and last stone placed in the arc was called the keystone The framework would be removed and was held in place by the pressure on the keystone As always arches need abutments

29

30 Bridges Modern Arc Bridges
Today arches are constructed out of concrete and steel Concrete arches are still made in the same way as stone arches Steel arches are made by connecting curved steel beams

31 Bridges Suspension Bridges
The best to build over large bodies of water A tower is built at either end, usually in the water A cable is strung from one side of the water to the other over the two towers On either side of the water on the embankment the cables are attached to huge concrete blocks called anchorages A roadway is hung from the cables The roadway is made strong by adding trusses along the side

32 load

33 Cofferdams A giant box that holds back the water
Provides a safe work area for excavation

34 Caissons A huge open ended box is set on the riverbed
The box is called a caisson When air is pumped in, water is forced out This provides a water tight space where people can dig up mud an stones When they reach the bedrock the caisson is filled with concrete and the tower is built on top of it

35 Bridges Cable Stayed Its towers connect directly to the deck
They do not need the large anchorages that suspension bridges do

36 Bridges Cantilever Bridge 2 beams project from opposite piers
Each beam is support at one end like a diving board The two beams meet in the middle of the span

37 Substructures Pile foundation All that is below the main floor
The building sits on it Pile foundation Large columns are dug or pounded into the ground

38 Substructures Raft foundation Extends past the edge of the building

39 Substructures Box foundation Like your basement at home

40 Superstructures All that is above ground Steel Skeleton construction
The frame of the building is constructed from steel columns and beams Often have cross braces

41 Superstructures Curtain Wall
Does not carry any of the load of the building It is attached to the steel frame work


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