Strengthening Bridges with Unbonded Prestressing

Abstract

This paper outlines the advantages and some of the practical considerations of unbonded prestressing, which has become a major trend in strengthening new and existing bridges. Its advantages include: (1) considerable simplification of the layout of tendons; (2) substantial loss reduction of prestressing forces due to friction; (3) easy control and correction of prestressing forces; (4) easy addition and replacing of tendons; (5) easy application of anti-corrosion systems; and (6) reduction of crack widths, especially in segmental bridges. The usual procedure to strengthen a bridge with additional prestressing tendons is to: (1) install additional anchorages, deviation supports, and tendon bundles; and (2) prestress the tendons to raise the prestressing forces. Some examples are given of practical considerations arising from unbonded prestressing. The cross girders may have insufficient load-carrying capacity, or may be closed. For T-team bridges, the prestressing anchorages can be taken up through the anchorage block. Linear prestressing is most often applied along a bridge's central axis. Curved bridges require a polygonal arrangement for the tendons.