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Bridges are structures that provide transportation over obstacles, such as valleys or bodies of water, by going over them. They were first used in ancient times when first civilizations began rising in Mesopotamia. It was from there  that the knowledge of bridge building spread beyond those borders, enabling the construction of bridges all across the world.

In the beginning, bridges were very simple structures that were built from common natural resources; wood, stone, and dirt. Because of this, they could only to cover very short distances, and they were very weak because the materials they used were easily dissolved by rain. Revolution in bridge construction came from Ancient Rome, where engineers found that dust made from grinding volcanic rocks  was an excellent material for making mortar. This enabled them to build much sturdier and larger bridges than any civilization before them. Seeing the need for roads to connect their vast empire, Roman architects spread across the Europe, Africa and Asia, using their knowledge to build bridges and roads.

One of the defining successes of Roman architecture was the invention of arches. By using this type of structure, load forces acting on the bridge were transferred along the curve of the arch to the ground, where they were nullified by the  supports on the sides of the arch. By using this new technique, Romans could easily produce cheap, light, and strong bridges from materials that could be found easily.

After the fall of Roman Empire, innovative bridge building techniques stagnated in Europe and Asia until the 18th century, when new age of science and engineering spread across the world. This came about from a new construction material, cast iron. Iron enabled creation of new bridge designs such as truss systems. Sadly, wrought iron did not have tensile strength to support heavy structures, which was fixed with the advent of steel and the ideas of famous French architect and engineer Gustav Eiffel.

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Many different forces act on bridges. No bridge is completely permanent. These forces will, one way or another, break any bridge. It is an engineer's job to try and delay this destruction for as long as possible by building the strongest bridge possible. Knowledge of the forces acting on bridges is crucial in this endeavor.

Compression- is a force pushing inward. An example of compression is two people leaning on one another with their hands out, so that their hands are compressed together. Another example would be a soda can squashed underneath a car as the car rolls over it.

Tension- is a force pulling outward. To explain it in terms of the previous example of compression, an example would be two people linking hands and leaning backwards, so that their arms are taut. Another example is a rope in a game of tug-o-war.

Torsion- involves two forces. When forces at opposite ends of a bridge rotate the bridge in different directions, torsion is acting on the bridge. An example is a dish towel being wrung out. In a bridge, however, a much more rigid structure is needed, so torsional effects are far more severe than those from a wrung dish towel. The torsion in the center of a bridge is zero, while torsion is greatest on the edge of the object it is acting on.

Shear- is a force that pushes ends of an object in different directions. For example, when a person sits on a bench, shear is present. The legs of the bench push the seat up, while the middle is pushed down by the person sitting on it.

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STEEL -Ilyas

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Iron: Used for beam and truss bridges. It is stable due to it being very strong against compression.
Steel: Made quickly and is resistant to tension and compression.
Concrete: Is a liquid before drying to a hard solid. It can be formed to any shape.
Plastic: Environment friendly. Are easy to clean and are maintenance free.
Wood: Light and strong and last for a long time. Is easy to repair and placed for bridges.

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Bridge from the Ottoman empire in Turkey

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Bridge from the Ottoman empire in Turkey

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One of the five maxims of the Shari'ah is: "Hardship Mandates Ease".
This means that when there is hardship, we should strive to bring about ease for the people. If people have trouble getting across water, we should create a bridge to make it easier for them to cross. This is indirectly instructing us to create bridges with the intention of making it easier for people.

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SOURCES: Benson, Mark. "The 7 Types of Bridges" engineeringclicks. engineeringclicks, Sept. 2019. Web. 3 Mar. 2020. Haskins, M. "What Is a Girder Bridge?" Civil Engineering. Civil Engineering, Jan. 2015. Web. 3 Mar. 2020.

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- The design looks simple, but it's super effective.
- The deck is the load-bearing element, and is held in place by cable-supporting vertical suspenders.

- Suspension cables extend beyond the sides of the bridge, and are anchored into the ground.

- Depending on the bridge size, a certain amount of towers will hold up the suspension cables, and these cables deal with the tension created by any load applied to the bridge.

[ ex. The Golden Gate Bridge ]

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- The name of this bridge refers to a supporting horizontal beams that can be made of stainless steel, concrete, or both.

- This is a common type of bridge where the deck is built above supporting beams that lay on piers and abutments, and support the span of the bridge.

- The beams used are often I-beam girders or box girder beams (made of steel or concrete, and shaped like an open box).

- These bridges are usually used for things such as pedestrian overpasses.

[ ex. The West Gate Bridge ]

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- One of the simplest types
- Deck consists of wood plank or stone slabs, supported on either sides by two beams that run between piers.

- The travel area is a simple decking stood vertically across the underlying beams, and there is no transfer of stress on this "simply supported" structure.

[ ex. The Newark Bay Bridge ]

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Cable-stayed: - Dependent upon load-bearing towers/pylons (connected to the deck by cables, either from the top of the tower or at different points of the column)

- This type of bridge is usually used for greater distances than cantilever bridges, but less than suspension bridges.

- A problem with this bridge is that the central connection of the cables puts pressure on the deck, which will then need to be reinforced.

[ ex. The Brooklyn Bridge ]

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- Works by using cantilevers (simple beams and trusses), made from pre-stressed concrete or structural steel.

- Two cantilever arms are connected by a "suspended span", which is a centerpiece which has no direct support underneath.

- The load is supported through diagonal bracing w/ horizontal beams (unlike the usual vertical bracing).

[ ex. The Quebec Bridge ]

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- Includes abutments, used to support the arch structure under the bridge.

- Most common is the viaduct (a long bridge made of many arches).'

- Lateral pressure the arch creates is transferred into supporting abutments.

[ ex. The Sydney Harbour Bridge ]

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- A load-bearing structure that efficiently yet simply incorporates trusses.

- Includes triangular elements that are able to absorb tension and compression, which is able to accommodate dynamic loads in the long run

- The tension/compression mixture makes sure that the structure of the bridge is maintained and that the deck is not compromised.

[ ex. The Sewickley Bridge ] .