Pre-Fabrication. Once the final bridge design has been completed, the design plans must be converted into fabrication plans and data. Steel plates often do not come is the size need, so they must be cut to the size needed. Steel is ordered to cover the total amount needed to complete the bridge and part.
Cutting and Marking. Once the steel arrives it must be marked and cut. Using data from a CAD system marking and cutting is performed by a gas and plasma NC torch. Marking is a process, which leaves important indicators on the steel to show the location of stiffening ribs and flanges. These markings become necessary during the assembly process.
Butt Welding. The process of welding one end of a steel plant to another plate to create a continuous plate that changes in thickness and or material. This process is generally performed using a welding process known as submerged arc welding.
Drilling. Once all the plates have been cut and butt-welded, any boltholes must be drilled. Again, the CAD generated fabrication data is used to insure highest quality. A high-speed NC gantry drill is used to drill the boltholes.
Panel Assembly. Once the plates are ready they must be assembled into the girder they are to become. There are two steps involved when fabricating a box girder or part of a steel deck. Large box girders and steel decks have many stiffening plates, which must be welded into the webs and flanges. Since it would be difficult to weld these stiffeners in place after the box girder has been assembled, they are welded into the flange and web plates creating panels for the final assembly.
Assembly, Welding and Correction. Once the panels are complete, the girder is ready to be assembled into its final form. Again tack welding is used to hold the flanges and webs in place prior to welding.
Trial Assembly. The final check before painting and shipping the members is the trial assembly. The whole bridge or sections of it are temporarily assembled. This is done to assure that the parts fit and everything is aligned perfectly before the product is shipped.
Machining. Machining also known as milling is a process in which steel is carved or ground away. On special projects, such as towers for cable stayed of suspension bridges, the adjoining block surfaces are required to come in perfect contact without gaps or spaces on as much as 50% of their contact area.
Blasting. Once the products pass the trial assembly test, they are ready to be painted. First all rust and dirt is cleaned off in blasting chambers. Blasting is done by literally blasting the steel with high-pressure air containing countless tiny bits of metal or sand known as shot. These little bits remove the rust, clean the surface and at the same time slightly roughen the surface of the steel, which helps the paint to adhere.
Painting. Once all the rust has been removed, the parts are painted to specification. Continuous monitoring of the painting process insures a perfect coat.
Lesson Plan I
Objective: research the history of bridges
Procedure:
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1) Students will be required to find out how the idea of a bridge was conceived and when and where was the first bridge constructed.
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2) Students will gather information on the characteristics of the six types of bridges covered in this unit, (beam, truss, arch, cantilever, cable stayed and suspension).
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3) Students will identify types of materials used to construct bridges.
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4) Students will use their information to choose a bridge they would like to focus on for this marking period.
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5) Each student will turn in a written report.
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6) Students will be encouraged to use the Internet to obtain information.
Evaluation: Work will be evaluated based on the information provided, neatness and correct grammar.
Follow-up Activity:
Students could use the Internet to find a picture and additional information on the bridge they chose, such as the longest bridge of its type and where it is located.
Lesson plan 2
Objective: 1) Visit a bridge
Procedure:
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1) Students will be required to visit a bridge, preferably in their neighborhood. This can be a group trip or an individual visit.
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2) Teacher will assist students in locating a bridge if necessary.
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3) Students will make a sketch of the bridge.
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4) Students will try to identify the type of bridge, and tell if it's a pedestrian
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or a vehicle bridge or both.
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5) Students will give a brief oral overview of their experience.
Evaluation:
Each student should have a sketch of a bridge. They should be able to describe the type of bridge it is and what it is used for.
