During the past few years, traf-fic loadings have increased steadily and the structural specification for bridges has changed. Many bridges built in the 1970s and 1980s now need strengthening or replacing. Assuming their foundations are adequate, simply supported and continuous structures can be strengthened by external prestress-ing. However, some structures may not be suitable for strengthening, because of inadequate foundations orrnunsuitable superstructures, such as concrete frames. In the following example, the existing flyover had to be demolished and a sophisticated system was developed to do this without using scaffolding or diverting roads.
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