Many civil engineers specialize in the design and construction of bridges. In this area, the engineer works closely with architects, urban planners, and other personnel to bring new bridges to final construction. In addition to considering its basic function, engineers must understand the social and environmental impacts of designing a bridge, determine the best location, ascertain the best building materials, analyze architectural and foundational aspects, and much more.
As the expert on the technical matters, it falls on the engineer to determine the mechanical aspects of building a bridge long before construction begins. While the architect is essentially responsible for creating the bridge design and aesthetic, the engineer must study these schematics in great detail to determine whether the bridge can actually be constructed. The engineer may even determine the type of structure even before the architect designs the bridge.
Understanding Types of Stress and How They Factor into Bridge Engineering
Fundamental to their design and construction is a basic understanding of the stresses to which bridges are subject. There are a number of types of stress, with the most common being compression and tension. Compression is the downward force applied to the bridge surface from the weight of the people and objects on it. Tension refers to the stress applied to the underside of the bridge from this same force. The engineer must analyze the amount of compression and tension the bridge is likely to undergo. This determines the possible types of bridges that can be designed, and the best and most cost-efficient materials that can be utilized.
Understanding the Types of Bridges and Their Appropriate Applications
- Beam Bridge This is the most basic bridge in which a strong horizontal length of material—commonly made of wood, concrete, or steel—is held up on each end by supporting structures. Beam bridges are usually most practical for shorter spans up to 200-250 feet. However, because the beam structure is only supported on its opposite ends, this type of bridge undergoes the most stress.
- Truss Bridge This variation of the beam bridge uses a series of connected metal bars in a triangular shape. This metal construction, called a truss, is attached to either the top (through truss) or the bottom (deck truss) of the bridge. This allows the beam to be extended to greater distances, because the material is more successful at handling different types of stress.
- Arch Bridge Arch bridges are very common, very sturdy, and can cover greater distances than beam and truss bridges. Much of its strength is due to the fact there is little or no tension in the arch design. While stronger than truss and beam bridges, the arch bridge can be more difficult to build.
- Suspension Bridge This type of bridge can span much greater distances, because of the innovative support provided by its cables. The bridge is connected to two large towers (usually made of steel), which are capable of accounting for all the compression force. The cables themselves account for the force created by tension. The building techniques used in traditional suspension bridges have now evolved to more advanced cable-stayed bridges, which ultimately require less material.
The engineering and building concepts behind these types of bridges—beam, truss, arch and suspension—can be applied in combination as well as separately in a number of designs.
One major point of concern in bridge engineering is the available materials that are to be used. Steel and concrete are the most common, but wood is still used, as are various types of metals, stone, and glass. The scale of the project, its location, and the type of bridge to be built largely determine what construction materials are best.
Other important factors when considering building materials are the esthetic quality of the bridge and the surrounding infrastructure. If the distinctive architecture of the general area must remain a focal point, a similarly looking bridge may be proposed. If the bridge location is a manufacturing or industrial site, a simple concrete design may suffice. In these instances, engineers must work closely with city planners to determine what is the most logical approach.
Considering Future Maintenance
One of the keys to successful bridge building that can be easily overlooked involves planning for future repairs. The impact of disasters, such as earthquakes or hurricanes, can affect how engineers approach their selection of building materials and the type of bridge to be built. Basic weather conditions are also a factor. Ice can cause great stress over time, and salt used to melt snow and ice can destroy a bridge surface. Effective bridge engineering incorporates long-term maintenance plans. Even better, bridges can be built in a manner that streamlines and eases future repairs.
Bridge Building Simulators
Games and simulations can be quite useful in educating and training bridge engineers. These interfaces allow engineers to gain hands-on experience in designing bridges under various conditions. Many simulators allow engineers to construct virtual bridges, and test the structure’s performance under different levels of stress and tension.
Bridge engineering is a specialized field of civil engineering that provides the opportunity to impact modern civilization in positive ways. Throughout history, bridges have served as a way to connect communities, enhance communication, encourage trade and commerce, and generally lift daily living. Many of the bridges that stand today serve as cultural and societal landmarks, and marvels of modern civilization.
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