A bridge inspection is a thorough evaluation of a bridge by engineering specialists for safety purposes. Periodic bridge inspections are required by law in many nations, while local regions may have their own similar requirements. These requirements often apply only to bridges that convey vehicular traffic such as cars or trains. The inspection will focus on the bridge’s structural integrity, drainage, and other issues that can affect safety. If a structure fails a bridge inspection, it can be closed for maintenance, renovation, or even demolition and rebuilding if necessary.
Modern traffic bridges are created with steel and concrete reinforcements mounted on bases in bedrock or densely packed earth. They cross bodies of water or sharp surface inclines, sometimes stretching distances that can be measured in miles or kilometers. Many carry thousands of vehicles on a daily basis and must be able to endure extreme temperatures or weather conditions. This involves complicated interrelated engineering principles such as metal expansion and fatigue, weight distribution, and traffic patterns. In the United States alone, more than 100,000 high-traffic bridges are subject to regular bridge inspection.
In the U.S., federal regulations require all bridges to be inspected every two years. States have their own regulations, some of which require more frequent inspections by local authorities. The inspection process also contributes to the accumulation of data that can be used to determine safety standards on a national or even international level.
A bridge inspection is carried out by a specially trained team of engineers. These engineers examine numerous details that can contribute to the bridge’s safety. In addition to those factors listed above, they will also check rust and metal stress, joints and connections, and lighting. Railings, road width, and even paint quality, which can protect against rust and deterioration, will also be inspected. Similar principles apply to train bridges and even some pedestrian bridges that are subject to inspection. Despite all these precautions, accidents do still happen.
On 1 August 2007, a bridge conveying traffic on a major north-south highway collapsed in Minneapolis, Minnesota; 13 people were killed, and scores of others were injured. Subsequent investigation revealed that a prior bridge inspection had given the bridge among the lowest of acceptable ratings. Officials aware of this rating had been unsure how to proceed, as engineers had determined that renovating the bridge would weaken it further. The cause of the accident was a previously unknown design flaw, undetected by repeated inspections, combined with the excess weight of construction equipment that was performing bridge maintenance. The incident led to a nationwide review of bridge safety and inspection policy.