Fifty-Year Development: Construction of Steel Arch Bridges

During the past 50 yr there have been major changes in the engineering, fabrication, and construction of steel arch bridges. The laser surveying instruments, high-strength steels, numerically controlled drilling, welding, and high-strength bolts have all had tremendous impact on field construction. The methods of erecting have also vastly improved the efficiency, time, and saftey of bridge construction. Erection methods vary from supporting the arch by falsework or wire rope tiebacks to jacking large heavy spans several hundred feet above river level. Fifty years ago, falsework was made of square timber formed into bents supported by wooden piles. Today, it is made from light reusable steel sections. Large floating derricks are used to lift heavy pieces, often eliminating the need for travelers mounted on the bridge.