A suspension bridge is a bridge that suspends the roadway with cables that extend from one end to the other. These cable rest atop two towers one opposite sides of the bridge. The weight from the roadway is transferred from the cables to the anchorages, which are usually embedded in concrete and located at the far ends of the roadways. The force of the weight on the cable is evenly distributed. The force of compression is usually applied to the deck, but the cables transfer the compression to the towers. Thus, the force is dissipated down to the earth, where the towers are steadily placed. The force of tension is usually experienced by the cables. The force stretches from each anchorage and stretch across the weight of the bridge. However, due to the anchorages being embedded in earth and/or concrete, the forces there are also dissolved. Most suspension bridges have a truss system underneath the deck. This helps to reinforce the deck and reduce the drift of the roadway to swaying motions. This application relates to the study of forces, especially the forces of compression and tension.
Suspension Bridges were first created in the early 7th century, although common, modern styles date from the 19th century. The earliest found bridges are located in Central America. Although the purposes are unknown, it is most probably an early transportation structure for the early American civilizations. At the start of the 19h century, modern technological advances allow the bridges to be constructed safely and allow for easier transportation of goods. Currently, engineers have used the traditional designs for a suspension bridge because of its useful and practical design. However, many variations of suspensions bridges have been formed. These variations are shown below and help expand on the aesthetic factors. The theory behind the physics of suspension bridges is very interesting since it shows how a massive structure, which is mostly supporting it's own weight, can stand and survive for decades without crumbling. Knowing how bridges are built and how to construct them is very informational since bridges allow for the transport of goods and trade, as well as communication applications between areas.



500px-Haer_PBG_erection_force_Diagram_part.png

bridge-suspension.gif
severn_bridge.jpg


  • Stressed Ribbon Bridge:
This type of bridge is related to the simple suspension bridge, but it is also stronger. This is because it not only relies on the tension in the support cables holding it, this one uses the compression of the material usually concrete, to hold it steady and so it sways less. To make the dip in the bridge is formed under high tensile force. (http://cedb.asce.org/cgi/WWWdisplay.cgi?7605075). Tensile force is almost the same as tension, but it is the force of tension pulling at two ends of an object. (http://www.matter.org.uk/schools/SchoolsGlossary/tensile-force.html). The tensile force along with the stress allows a sturdy structure. The stress is based on the amount of area and total force. stress1.gifThe compression and the stress together forms a more rigid and sound structure. But another way to add stiffness to the structure is the arches, used to support it from underneath. But this type is also very sensitive to wind and large temperature changes and weight. (http://www.vbt.bme.hu/phdsymp/2ndphd/proceedings/kulhavy.pdf). The temperature changes allow for the concrete to expand and contract, which is why they are not widely used structures and they when they are built are built in places where there is little to no climate change.
440px-Puente_Barra_Maldonado_%28Punta_del_Este%29.jpg
  • Simple Suspension Bridge:
A Simple Suspension bridge is more commonly known as a rope bridge or a hanging bridge and is the simplest form of a bridge. It is held in place by being held down on two sides over a river or a valley. These bridges being less stiff than other types are more easily swayed because of wind or the weight of a person moving on it. (http://en.wikipedia.org/wiki/Simple_suspension_bridges). The handrails allow for more support. But the amount of motion in the bridge inspired other types of bridges to be built, for example the stressed ribbon bridge, which is almost the same thing except with a high amount of stiffness in the pathway, which is made of concrete, whereas the simple bridges need to be built lighter and so uses materials like rope and wood. The simple bridge is made with a downward arch in the bottom because of the lack of tension in the walkway. If the stiffness was higher it would be harder to support weight. (http://www.spiritus-temporis.com/suspension-bridge/).

capilano-suspension-bridge.jpg

Underspanned Bridge

This type of bridge is very rare due to its strange, possibly unstable design. The deck is raised on posts above the main cables. The deck is more unstable than those who have the deck hung on cables. A famous underspanned bridge is "Le Pont des Bergues" by Guillaume Henri .


800px-Micklewood-bridge-x2.svg.png


images.jpeg

Self-Anchored Bridges [edit]

A self-anchored suspension bridge is a bridge that does not have anchorages ataching the cables to the ground. Instead, the cables are attached to the ends of the deck. This causes a force of compression to be experienced equal to the tension force in the cables. This design allows the bridge to not exert any horizontal forces onto the ground. The bridge only needs to support it's own weight. It is also appropriate for areas where anchorages would not be possible, due to unstable soil.

180px-HAER_Hutsonville_04_065813pv.jpg<The anchor for a self-anchored bridge




However, there have been times when bridges have failed to withstand nature. Some of these disasters include The Silver Bridge and The Tacoma Narrows Bridge. The Silver Bridge was constructed in 1928 over the Ohio River. It was a eyebar chain suspension bridge. Unfortunately, in 1967, the bulk of rush hour traffic caused it to collapse, causing 46 casualties. The failure was attributed to a single eyebar chain that was 0.1m long. t was also hypothesized that the bridge was carrying heavier loads than it was designed for. The Tacoma Narrows Bridge was built in 1940 in washington. The collapse occured just a few months after its completion. Altough it was designed as flexible to withstand major winds, the collapse was attributed to strong winds. However, the fatal winds were a third the speed the bridge was designed to handle. There were no casualties fortunately.
180px-Silver_Bridge,_1928.jpg180px-Silver_Bridge_collapsed,_Ohio_side.jpg
[Silver Bridge after completion] [Silver bridge after collapse]

Image-Tacoma_Narrows_Bridge1.gif180px-Tacoma_Narrows_Bridge_Falling.png
[Tacoma Bridge at completion] [Tacoma Bridge collapse]


http://en.wikipedia.org/wiki/Suspension_bridge
http://www.pbs.org/wgbh/nova/bridge/meetsusp.html
http://en.wikipedia.org/wiki/Silver_Bridge

SOMEWHERE ON THIS PAGE YOU MUST PRESENT YOUR “ESSAY” IN WHICH YOU ADDRESS THE QUESTIONS LISTED ON THE PROJECT OUTLINE AND THOSE BELOW. BE SURE TO HAVE THIS PART SEPARATE FROM THE CUT AND PASTE AND EMBEDDED ITEMS THAT YOU HAVE INCLUDED. YOU MUST REFERENCE (URL) ANY OUTSIDE SOURCES OF INFORMATION. THIS 500 TO 1000 WORD ESSAY MUST BE IN YOUR OWN WORDS – NOT CUT AND PASTED FROM A WEB SITE.
SPECIFICALLY:
WHAT EQUATIONS OR THEORY DID WE LEARN THAT RELATES TO YOUR TOPIC?
WHAT IS THE HISTORY OF THIS TOPIC?
WHAT IS THE CURRENT LEVEL OF RESEARCH OR APPLICATION OF THIS TOPIC?
WHERE IS IT HEADED IN THE FUTURE?

WHAT HAPPENS WHEN A SUSPENSION BRIDGE FAILS? WHAT CAUSES IT TO FAIL? LOOK FOR HISTORY OF THESE BRIDGES AND THEIR CATASTROPHIC FAILURE MODES.

William Chan - What are the advantages of suspension bridges as compared to other bridges?

Suspension bridges are advantagous because of their structure. They are more stable due to the incorporation of cables and anchors which connect the bridge to the ground. The weight of the load is evenly distributed by the towers and anchors and transfer the weight to the ground.

Robert Lopez - What is the most stable of the types of bridges and are there certain locations on earth where a bridge would be more stable?

The most stable type of bridge is the suspended deck bridge. This type is the most commonly built type of suspension

Brandon Siegenfeld- Why did the Tacoma Narrows Bridge fail?

The Tacoma Narrows Bridge failed to keep its structure because of its

Sam Edwards - Does flexibility make suspension bridges more structurally sound or less structurally sound?

Flexibilty is required because the bridges must be able to flow with the wind. The bridge should not be an obstacle to the path of the wind but it has to retain its shape and form. However, flexibilty has a limit since the bridge cannot be unstable. [i.e. the Tacoma Narrows Bridge]

James Song- When an x-ray is taken of the bridges, does it affect the molecules and could it lead to weakening of the bridges?

I have no idea how one would take an x-ray of a bridge.

Greg Sturm - How are these bridges built if there is nothing to stand on in the middle? You could use boats I guess, but did people in the 7th century have access to that kind of stuff?

Primitive bridges weren't as elaborate as bridges are today. These structures were usually tree logs that were put

Douglas Chin - Does a suspension bridge always need two towers? Or could there just be one central tower with the cables running either side of it?