Bridges can expand or contract due to various factors, including temperature and traffic load. Expansion rollers are built into the truss support system of bridges to allow for safe expansion and contraction. Corrosion can damage expansion rollers, leading to bridge collapse, as seen in the 2007 Interstate 35 West Bridge collapse in Minneapolis.
Bridges can expand or contract due to many factors, such as traffic load, materials used in construction and temperature. For example, when the temperature is warm, a bridge expands in length, and when the weather gets colder, it contracts. An expansion roller allows a small bridge of rigid construction to expand and contract in length safely.
An expansion roller is a mechanism built into a bridge’s truss support system. The truss is the triangular structure of the bridge, with all parts connected by intersections called nodes. The expansion roll consists of joints constructed of bars that move as the deck expands. Expansion rollers are included on bridges 80 feet (24.4 meters) and longer to ensure bridge safety at all times. While the expansion and contraction of each section of the bridge may be very small, as bridges stretch, this can become quite a big problem.
As temperatures rise, the materials used to build the bridge can expand or increase in length. The more the temperature increases, the more the materials will rise. The expansion rollers allow the sections to move so the extra length does not cause the deck to warp and even break. As temperatures get colder, the bridge’s building materials will contract or shrink in size. In this case, the expansion rollers allow the parts of the bridge to move so that they mesh and no gaps are created in the bridge.
Factors other than weather conditions can also cause a bridge to expand and contract. Expansion and contraction can be caused by the curing process of the concrete, earth moving, and heavy loads moving across the bridge over an extended period of time. An expansion roller is a type of bearing that makes these otherwise harmful factors that are not harmful to the deck.
Bridges need to be inspected and checked regularly, like the rest of the transport and highway infrastructure. An expansion roller can corrode and become ineffective due to road salt, dust and ageing. Corrosion is the most common damage affecting the durability and life of a bridge. For example, in 2007, the Interstate 35 West Bridge, in Minneapolis, Minnesota, collapsed due to frozen, corroded, 40-year-old expansion rollers malfunctioning. The lack of expansion capability was due to a damaged expansion roller and led to pent-up stresses in the bridge and the buckling and collapse of an integral horizontal girder.
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