Truss Bridge Design Essay

1. What is a truss and how are trusses used in bridge design? Include the importance of triangular shapes in truss design. A truss is a formation produced by triangular components. The triangular units forming the truss are slim and straight in form. The truss bridges consist of a grouping of triangles. Trusses are used in bridge design to form a series of strong supports using triangles, and have the forces of tension and compression acting on them. The importance of triangular shapes in truss design is that when a force is applied on them, they will be under both compression and tension.

The forces will be spread sideways, which spreads the weight from where it is applied, to the ends of the bridge. A truss is a structural formation of triangles created by individually bonded parts. These parts are mostly straight, and can strongly support a bridge. The trusses are usually used in bridge design, because of the geometric principles in play. With the minimum amount of materials, this design will be the strongest and the lightest. Because of the properties of a triangle, the sides will not bend, therefore the angles with not change and the bridge will stay strong.

Determine the purpose of a superstructure and substructure The superstructure is the part of the bridge structure that is above and includes the baseline. The superstructure receives the load and its purpose is to support the weight of the load that is placed on top of it. The superstructure contains the overlying framework and uses tension to holds up the bridge. In real life, the superstructure also has the purpose of protecting a bridge from forces, such as earthquakes. The substructure is the part of the bridge structure that is below the baseline.

The substructure contains the foundation of the bridge and its main purpose is to support the superstructure from beneath it. It also has the purpose of transferring the load to the foundations. The superstructure and substructure work together to prevent the bridge from breaking. State the general relationship between the strength and mass of a bridge then the general relationship between the strength and mass of a bridge is that the larger the mass, the stronger the bridge will be.

Strength and mass are proportional, since an increased mass allows for more materials to maintain the structure. Increased supports mean that there will be more supports for the applied load. Another important relationship between strength and mass (material used), is that shorter members are less capable to compression, while longer members are better for obtaining tension. Research of Bridge Designs Warren Truss Bridge: It is considered one of the simplest and strongest bridges. It uses equilateral triangles.

The equilateral triangles minimize the forces to only tension and compression. When the load is centered in the middle of the bridge, all the forces are larger. Its advantages are that it is fairly simple, and spreads loads fairly evenly between the members. The disadvantages are that it has poorer performance under certain loads. It is best used for long span structures. Pratt and Howe Tresses: These two bridges are very similar. The only difference is how the slanted members are angled.

On the Pratt truss, the shorter, vertical members are in compression, hereas on the Howe truss, the angled members are in compression. The Pratt Truss has larger forces on the top and bottom chords than the Howe. There is a similar effect of centered and spread loads on the Howe Truss. These designs are not advantageous when the load is centered. Fink Truss bridge: This is one of the more commonly used typed of construction trusses. It is a symmetrical truss that has arms which angle upwards from the bottom chord, forming V-shaped webs, which supports the interior of the structure.

This structure can be duplicated, by making a double fink truss, or a triple fink truss. They were frequently used in bridges for railroads. However, they are now commonly used as roofing trusses nowadays. It has a 35° pitch. Conclusions about bridge design and how conclusions apply to bridge design for this project. Regarding bridge design, we have learned about the different types of truss bridges and how they are used. As well, we learned about the pros and cons of different types of truss bridges namely the Warren truss, Pratt and Howe trusses, and the Fink truss.

Additionally, it was concluded from the research that triangles will experience both tension and compression when a force is applied on them, since the triangle spreads the compression force sideways to the ends of the bridge, therefore allowing support for a maximized load. Equilateral triangles are commonly used as they minimize forces to tension and compression. From the bridge research, it was concluded that the first types of bridges such as the Warren truss and the Pratt and Howe trusses are not optimized to keep a load; this crates the decision to construct a Fink bridge.

The reason for this hoice is that the Fink design is with a large triangle, with numerous smaller triangles inside the large triangle for reinforcements, which signifies that the Fink design would be strong, especially if the load is applied to the middle, due to the strengths of triangles. Additionally, to further strengthen the bridge for a centered load, the bridge should have a high depth at the middle. Also, in order to ensure that the bridge spans at least 90 cm, and to add strength, it was decided that a Triple Fink bridge be constructed. Due to the triangles in the design, this is even further reinforced by the overall triangular shape.