Justify your choice of bridge design. Provide research that justifies your choice
Through the many years bridge designs have changed dramatically, from few pieces of log being tied together to enormous suspension bridges span over hundreds of kilometres. As the technology and knowledge advanced the designs of the bridges became bigger and stronger.
The bridge design which was chosen uses the Pegram Truss, which is a hybrid of Warren and Parker’s truss design. This particular design allows existing bridges to be recycled, meaning that the components of the original bridge can be reused and changed into the design.
The Pegram truss is also able to be reassembled, which allows adjusting the span of the existing bridge. Since this design is able to use existing components of existing bridges it will help consumers to save more money rather then building a whole new bridge. It will also produce less pollution compared to building a bridge from scratch. This characteristic is some of the needs and demands of current society have on being environmentally friendly.
Since this design is a hybrid of Warren and Parker’s truss design, not many of these type of truss bridges have been made. This is also one of the reasons why the design was chosen. The design that was made had slight changes to the angles which are suppose to be at a 60-70 degree angle. In the original design the entire bridge is made up of iron, however rather than using all balsa wood pieces, I changed the diagonal trusses to string, this will allow the bridge to withstand the tension that is given to the supports when load is present.
http://prezi.com/t8-aj6js4s2g/bridges-trusses/ http://www.brighthubengineering.com/structural-engineering/63635-truss-bridge-designs/ h...
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...s then it should. Also some of the balsa wood did not reach the other corresponding side causing the bridge have is torsion stress (shown in diagram 3) causing the twisting bending which was shown during the last few second before it gave way.
How could you have made improvements to your bridge?
Improvements that could be made are to make sure that the balsa wood is accurately cut into the same length pieces; this will decrease the amount of shear that the bridge will face while holding up the load. Other improvements can be things like having a constant pattern in how the strings are tied around the bridge (shown in the diagram below); this will allow the tension to be more equally distributed across the bridge. The quality of the starting balsa wood should be considered and check at the beginning to increase the strength of the supports holding the load up.
Without a concrete reason for the bridge's failure, every suggested reason was researched until proven incorrect” (Silver). There were many reasons that were suggested, but could not be proven correct due to the collapse. Wikipedia states that “A small crack was formed through fretting wear at the bearing, and grew through internal corrosion, a problem known as stress corrosion cracking.” The failure of the bridge was caused by a defect in one of the eye-bars on the north side causing the other side to collapse as well. “Stress corrosion cracking is the formation of brittle cracks in a normally sound material through the simultaneous action of a tensile stress and a corrosive environment.
Bridge efficiency is important as it helps reduce cost of building while maximizing the strength of the bridge. Many things can influence the bridge’s strength and weight, but the two main things that can cause a bridge to be a failure or success is the design of the bridge and construction of its joints. In order to build a potent balsa truss bridge, it is crucial to know how the layout of members and style of gluing can help increase or decrease strength.
In 1962, Hurricane Frieda blew across the property wreaking havoc, but the bridge stood unharmed. Recently in the winter of 2006, a 93,000pound, 9.4 meters, 300 year old Douglas fir tree fell on the western part of the bridge. The cables did not snap under the loading, but the bridge was closed for three months for renovations. During this time, the tree was removed from the bridge and testing was done. Also the supporting concrete on either side of the bridge was upgraded to 114tons (Capilano Suspension Bridge Park par.
This bridge was necessary to the people of Harpswell due to the weather changes making it impossible for the fishermen and their families to cross from island to island. They used their fishing boats when the weather cooperated, but when storms arose and when the water
The 1.78 mile western span of the bridge between San Francisco and Yerba Buena Island presented the first obstacle. The bay was up to 100 feet deep in some places and required a new foundation-laying technique. Engineers developed a type of foundation called a pneumatic caisson to support the western section. A series of concrete cylinders were grouped together and then capped-off, having the air pressure of each cylinder identical to balance the beginning of the structure. From there, the workers added sets of new cylinders until the caisson reached the bottom of the bay. Then, in order to reach the bedrock, they inserted long drills down the cylinders, digging until they reached bedrock. After the caisson was balanced at the bottom of the bay, workers filled it with 1 million cubic yards of concrete, more concrete than was used for the construction of the Empire State Building! This caisson connected the two suspension bridges that make up the western part of the bridge.
The Golden Gate bridge, standing as an icon of roadway innovations, took multiple engineers years to design and complete. They could not just simply build an ordinary bridge. They had to take into consideration the physics behind it, as well as, what kind of effect the environment would have upon the bridge. The bridge sits along one of the most active fault lines in the world, so engineers had to make sure their bridge could withstand a little movement. Today the Golden Gate bridge still stands tried and true, as does many other innovations that 20th century engineers came up with.
At the time of its construction in 1929, the Ambassador Bridge was the largest spanned suspension bridge at 564 meters until the George Washington Bridge was built. It was an engineering masterpiece at the time. The total bridge length is 2,286 meters and rises to 118 meters above the river. Suspension cables support the main span of the Ambassador Bridge and the main pillars under the bridge are supported by steel in a cantilever truss structure. In total, the McClintic-Marshall masterpiece is comprised of 21,000 tons of steel. The immense socio-economical impact that the Ambassador Bridge has on transportation and trade is imperative for daily interaction between the Un...
Bering Land Bridge- during it’s time of existence the bridge was a major factor in migration from Asia to North America; made travel easier because it was on land instead of having to travel by boat
The process of designing, building and inspecting the bridge had plenty of assumptions. Training on the strength of gusset plates would have mitigated those assumptions with expertise.
The architecture and engineering firm hired with the task of designing and constructing the tower, SOM, assigned Bruce Graham and Fazlur Khan to the project. They implemented a bundled tube design that was the first of its kind on such a large project that paved the way for the design and construction of future skyscrapers. This design allowed for 4.5 million square feet of office space, more customization of the floor layouts, up to 3 foot of sway within the building, and the stiffness needed to stay standing at the height in which it was built. The tubular design also allowed Sears to save about $10,000,000 on steel alone compared to previously used steel frame designs. Additionally, SOM managed to save 95% of the time usually spent welding by using prefabricated parts referred to as Christmas trees. This not only majorly sped up the process, but allowed Sear to save on labor costs. In addition to 3 trussed layers in the building, there were trusses and spandrel beams designed into every floor to help the load distribute more evenly.
The Tacoma Narrows Bridge is perhaps the most notorious failure in the world of engineering. It collapsed on November 7, 1940 just months after its opening on July 1, 1940. It was designed by Leon Moisseiff and at its time it was the third largest suspension bridge in the world with a center span of over half a mile long. The bridge was very narrow and sleek giving it a look of grace, but this design made it very flexible in the wind. Nicknamed the "Galloping Gertie," because of its undulating behavior, the Tacoma Narrows Bridge drew the attention of motorists seeking a cheap thrill. Drivers felt that they were driving on a roller coaster, as they would disappear from sight in the trough of the wave. On the last day of the bridge's existence it gave fair warning that its destruction was eminent. Not only did it oscillate up and down, but twisted side to side in a cork screw motion. After hours of this violent motion with wind speeds reaching forty and fifty miles per hour, the bridge collapsed. With such a catastrophic failure, many people ask why such an apparently well thought out plan could have failed so badly?(This rhetorical question clearly sets up a position of inquiry-which iniates all research.) The reason for the collapse of the Tacoma Narrows Bridge is still controversial, but three theories reveal the basis of an engineering explanation. (Jason then directly asserts what he found to be a possible answer to his question.)
However, before doing this we had to look more into depth on the materials we will use to construct our bridge. We also have to consider the possible environmental and geological factors that should be taken into consideration for our model. Pertaining to environmental and geological factors, there are many stipulations that structural engineers take into consideration before the construction of a truss bridge begins. The main objective of the geotechnical engineers are to protect the lives of others and avoid property damage from happening which can be caused by various geological conditions. Geological engineering uses principles of soil and rock mechanics to find surface conditions and materials.The Geotechnical engineers complete works such as: geological hazard assessments, material properties, landslide and slope stability, erosion, flooding, dewatering, and seismic investigations. These engineers closely examine all of these important factors before constructing a bridge in a certain location. According to Teach Engineering.com, constructing a safe and efficient bridge requires an ample amount of time and energy. Environmental and geological factors play a major role in construction, as
Every suspension bridge is different, but they all work in the same way. The roadway doesn't rest on supports. Instead it hangs in the air, suspended from thick cables. Only two towers are needed to hold up the cables, and they can be placed far apart to keep the river open for boat traffic. Finally in 1867 The New York Bridge Company made John A. Roebling engineer. In just three months he produced all drawings, cross sections, location plans, preliminary surveys, estimated cost, took sounding, and wrote his proposal. In June of 1869 John finished the design for the bridge. He and Washington climbed out onto the end of a pier to determine the exact l...
Our bridge consists of three levels supported by 1" high cylinders to support each level. On each level we will have rows of both three and four cylinders extending across the middle. Each cylinder will be stacked on another, evenly offset and centered to gain support. Our bridge will be 28" X 2 -7/8". The length of our bridge is probably the biggest and most significant contributor to our outcome. The desk table gap is 14" long, while our bridge length is 28" long. This shows that we would only be testing a small portion of our long bridge. It is significant because we have the advantage of having twice the amount of supporters, while we will be only testing a small portion of our bridge. With all of our cylinders we know that this bridge will evenly distribute weight.
For this bridge its fall was inflicted by an unknown patron. One who’s identity or existence we never see verified. The record of the fall is short in the story described as only being for a moment. Then the bridge was finally introduced to “the sharp rocks which had always gazed up at me so peacefully from the rushing water”. Rocks gazing peacefully? This is almost as absurd as a bridge turning around. An action that the bridge itself cannot seem to believe it is doing. This attempt by the bridge was his final effort before his fall. I cannot even picture how a bridge would turn around and attempt to look on his back. The question that comes to my mind is how can a bridge see what’s on his back? If this book is trying to make us believe that this bridge is a human, or has human like qualities. Then how flexible a person is this bridge? Because I know very few people who can see whats on their back. Especially without turning so much that anything on their back would fall off. So is this bridge so inflexible that it breaks itself by turning around or is it trying to buck off its attacker unintentionally? This answer is never answered due to the story ending shortly thereafter this scene. With the short fall of the bridge onto the sharp rocks it had stared at for the entirety of its life. The events before and during the fall of the bridge was the main issue I had with my thesis that the bridge was