Bridge Strengthening with Additional Prestressing

Abstract

This paper discusses the application of additional prestressing tendons for rehabilitating and strengthening bridges, which has been widely used during recent years. Additional encased tendons in a widened cross section use proven prestressing systems. Various types of external tendons have been investigated; they have different cross section, sheathing, deviation points, anchoring methods, corrosion protection, and application to existing structures. Thorough analysis, design and construction are required to anchor additional prestressing tendons, where forces of up to 5MN and more are transmitted to the existing concrete structure. In general, the use of prestressing tendons, either encased in concrete or installed externally, is an effective technique to: (1) strengthen bridges; (2) prevent further cracking; (3) re-establish the compression forces of an uncracked condition; and (4) control stresses and deflections. Two case studies are given of the technique's application: (1) strengthening, with encased tendons, of a four-span continuous prestressed concrete motorway bridge, built in 1963; and (2) strengthening, with external tendons, of a three-span continuous prestressed concrete box girder bridge.