STRUCTURES
WHAT IS A STRUCTURE?
A STRUCTURE IS SOMETHING THAT WILL SUPPORT AN OBJECT OR A LOAD. A STRUCTURE MUST BE STRONG ENOUGH TO SUPPORT ITS OWN WEIGHT AND WHATEVER LOAD IS PUT ON IT !
1. STRUCTURAL CONDITIONS
STABILITY: IT IS ASSOCIATED TO THE POSITION OF THE CENTRE OF GRAVITY. LOW CENTERS OF GRAVITY AND WIDE BASES PROVIDE BETTER STABILITY.
HOW CAN WE IMPROVE STABILITY?
Lowering the gravity center
Adding braces or support wires
Increasing the platform size.
RESISTANCE: IT IS THE CAPACITY TO BEAR STRESSES WITHOUT BREAKING. IT IS DETERMINED BY THE STRUCTURE’S SHAPE AND THE MATERIAL USED TO IT.
HOW CAN WE IMPROVE RESISTENCE?
Using different materials
Changing the shape of the structure.
RIGIDITY: THE DEFORMATIONS OF AN OBJECT MUST NOT PREVENT IT FROM FULFILLING ITS FUNCTION.
HOW CAN WE IMPROVE RIGIDITY?
Triangulation Apply a pushing force as shown, and observe what happens to the frame.
Can you think of anything that can be done to prevent the structure from deforming like this?
ACTIVITIES
1) Copy these sentences in your notebook and choose the correct option:
a) The shelf is curved because it couldn’t bear/act on the weight of those heavy books b) The resistance of a structure is determined/exerted by the material is made from. c) The pressure of the water in the tank has deformed/resisted the sides.
d) A stable structure is one that is safe and will not fail under the conditions/resistances for which it is designed.
2) How was stability improved in these structures?
4) Watch this picture. Can you find a way to make the pole more stable? Draw three possible solutions
5) Repeat the previous activity with this picture: now we need to support the horizontal bar on the vertical pole:
6) Add bars to these structures in order to get triangles, so that they will be rigid.
STRUCTURAL ELEMENTS
1º FOUNDATION: MADE OF REINFORCED CONCRETE THAT SUPPORTS ALL THE WEIGHT.
3º PRIMARY BEAM AND SECONDARY BEAM ARE ARRANGED TO SUPPORT THE FLOOR (BLUE AREA )
4º ARCH. LIKE A SINGLE BEAM BRIDGE, THE ARCH TRANSFERS THE LOAD TO THE FOUNDATIONS
ACTIVITIES
7) The structures shown below are famous and well known. Write the name of each structure under
8) Write the names of the structural elements shown in each picture.
BRIDGES
SUSPENSION BRIDGE
A suspension bridge is a type of suspension structure. There are several beams which are hold by dozens of steel wires.
They could have 2 or more columns, which support all the weight. The space between two columns is called Span.
This type of structure is very good for covering large distances (large span ) but are very expensive. It can span 700 to 2300 feet -- way farther than any other type of bridge! Most suspension bridges have a
truss system beneath the roadway to resist bending and twisting.
Suspension Bridge: Forces
In all suspension bridges, the roadway hangs from massive steelcables, which are draped over two
towers and secured into solid concrete blocks, called foundations, on both ends of the bridge. The cars push down on the roadway, but because the roadway is suspended, the cables transfer the load into
compression in the two towers. The two towers support most of the bridge's weight.
THE BEAM BRIDGE
down on the piers. The farther apart its piers, the weaker the beam becomes. This is why beam bridges rarely span more than 85 meters.
Beam Bridge: Forces
When something pushes down on the beam, the beam bends. Its top edge is pushed together, and its bottom edge is pulled apart.
THE TRUSS BRIDGE
A truss is a structure composed of members connected together to form a rigid framework.
Members are the load-carrying components of a structure. In most trusses, members are arranged in interconnected triangles, as shown below. Because of this configuration, truss members carry load primarily in tension and compression.
Truss Bridge: Forces
Every bar in this cantilever bridge experiences either a pushing or pulling force. The bars rarely bend. This is why cantilever bridges can span farther than beam bridges.
THE ARCH BRIDGE
It has great natural strength. Thousands of years ago, Romans built arches out of stone. Today, most arch bridges are made of steel or concrete, and they can span up to 275 meter.
Arch Bridge: Forces The arch is squeezed together, and this squeezing
supports, called abutments, push back on the arch and prevent the ends of the arch from spreading apart.
ACTIVITIES
9) Write the type of bridge that you can see in each picture:
Akashi Kaikyo Bridge, Kobe and Awaji-shima, Japan
Brooklyn Bridge, Manhattan and Brooklyn, New York, 1904
Garabit Bridge, Massif Central, France Golden Gate Bridge, San Francisco and Sausalito, California
Iron Bridge, Coalbrookdale, England
Tower Bridge, London, England
10) Welcome to Craggy Rock!
You got here just in time. This growing community needs four new bridges, and they're very picky about what they want!
Test your engineering skills and try to match the right bridge to the right location.
Location 1: Multi-lane bridge for commuters and tourists Location 2: Footbridge across a stream
Location 3: Highway bridge across a busy shipping port Location 4: Railroad bridge in a national park
