Bridges Presented by: Jawad Abdul Sater & Ahmed Al shoibi
Forces • Before we take a look at bridges, we must first understand what are forces. • What is a force?A force is a push or a pull • How can we describe forces?Lets take a look at Newton’s law
Newton’s Laws • Newton’s First lawan object at rest will stay at rest unless acted upon • Newton’s Second lawF=mass*acceleration • Newton’s Third lawfor every action, there is an equal and opposite reaction
What do the laws tell us? • For every action there is an equal and opposite reaction • A force is being exerted on the box. Therefore the ground must also exert a force on the box equal to the weight of the boxcalled normal force
Bridges • Now that we have a rough understanding on forces, we can try relating them to the bridge. • A bridge has a deck, and supports • Supports are what holds the bridge upForces exerted on a support are called reactions • Loads are the forces acting on the bridge
What is a bridge? • A bridge is defined as a structure built to stretch over a valley, road, body of water or other physical obstacle so that a passage can be made
Who and when? • The first bridges ever created were naturally made. Then stones and wood were used and so forth. One for the oldest bridges (arch bridge) in the world is the Pons Fabricius Bridge in Tome. it was about 5.5 m wide.
A bridge’s uses • The bridge is designed for pedestrians, railroad cars; to carry overhead power lines, motor vehicles, trains, and even a pipeline or act as a waterway for transport and much more.
Three Forces • On a bridge there are always three forces acting upon it; the Dead load (force exerted by a bridge from its own weight) • dynamic load (force applied on a bridge from unusual environmental factors like earthquakes or strong gusts of wind) • live load(fore put forth on a bridge due to traffic moving across the bridge). These three forces are taken into consideration when designing any type of bridge
Kinds of bridges • Beam bridge • Arch bridge • Suspension bridge • Truss bridge • Cantilever Bridges
Beam bridge • Also known as the simples bridge • Generally located at fixed gaps and provide additional reinforcement • The deck is usually made of reinforced concrete or metal.
Cantilever Bridges • Have two cantilever arms extending from opposite sides of the obstacle to be crossed • Built using cantilevers which are horizontal beams; supported on only one end • Large cantilever’s use trusses built from structural steel Arch bridges • Arch-shaped and have abutments on each side • The load of an arch bridge is carried outward along the curve of the arch to the supports at each end.
Arch bridge • Arch bridges • Arch-shaped and have abutments on each side • The load of an arch bridge is carried outward along the curve of the arch to the supports at each end.
Suspension Bridge • Suspension bridges • The deck is hung on suspension cables on vertical suspenders • Longer main spans are achievable than with any other type of bridge
Truss bridge • Made of connected elements (typically straight). Truss bridges are one of the oldest types of modern bridges • Timber, iron, steel, concrete are what they are usually made of.
How strong • Bridges have many stressors. Most bridges are made of wood, brick, stone, iron, steel, aluminum, and steel-reinforced concrete. • Some stressors a bridge has to withstand are: bending, compression, impact, oscillation, pressure, tension, vibration, erosion, expansion, fraction, rain, sea water, temperature changes, tidal flow, turbulence, wind gusts, and on top of that wind pressure. So as you see a bridge is not protected or covered in any way shape or form, so it has to be able to withstand all sorts of changes.
Construction and Preparation • Before a bridge is built there are many things that have to be taken into consideration. Surveying from professionals like archaeologists and geologists are taken. Weather patterns, water run-off, snow levels and even the weight of vehicles are taken into consideration. Even the type of geography influence what type of bridge is built.
Construction and Preparation • Suspension bridges take a long time to construct. They require supports with long cables to hold up the road from the anchor towers at either end of the bridge. The main forces in a suspension bridge of any type are tension in the cables and compression in the pillars.
Construction and Preparation • For example a person may chose to build a suspension bridge instead of an arch bridge if money was an issue, distance or even weight. Builders also have to consider the physics concepts when building like: distance (how far the bridge should be), energy (wind) and also force.
Practical Application & Societal Impact • Bridges allow people to receive goods and also to travel from one place to another. They aid many people and help industries a great deal. Bridges save a lot of time and money. These direct paths from one place to another are very important. • Bridges help the economy and businesses to thrive. Communities are able to develop in areas that they may not been able to without a bridge. • Bridges have been able to connect many countries such as china through importation and exportation and have developed very large networks in distribution many things such as: coal, food, oil etc…
Division of physics • Bridges and its construction fit into several divisions of physics. Kinematics, motion and forces, energy, waves and sound are used when dealing with bridges, when constructing a bridge the distance and speed are very important when deciding where a bridge should be placed. • The bridge should not have the same (resonance) natural frequency of the wind (cause it to swing) as stated in the beginning of the slide. • Gravity also has an effect on bridges; gravity transfers forces to the structures that support the bridge.