Strengthening Prestressed Concrete Box Girder Bridge by Upgrading Structural System

Abstract

The Yellow River Dongming Highway Bridge (YRDMHB) is a prestressed concrete rigid frame-continuous girder bridge located in Shandong Province, China, constructed in 1993. After 10 years of operation, a deflection of 150 mm was observed at the midspan of the bridge, and this deflection had a considerable negative influence on the serviceability of the structure. This research presents a strengthening process for the YRDMHB using stay cables to mitigate the midspan deflection. Specifically, the girder structure is modified to a pseudo-cable–stayed bridge by adding an extension system, which consists of two pairs of stay cables, towers, and joist-bracket structures. Furthermore, steel joist-bracket structures are added below the four sections of the main girder to anchor the cables. The load of the girder is shared by the cables and transferred to the new main towers, changing the internal force and line shape of the girder. Through this strengthening method, the original girder structure is upgraded to a cable-girder cooperative work system. The strengthening work includes theoretical analysis, laboratory tests, plan implementation, and field load tests. First, the strengthening scheme using stay cables is illustrated and laboratory static load tests are conducted to verify the applicability of the proposed plan. Second, the strengthening scheme is implemented and the key mechanical and geometrical parameters are monitored. Third, to examine the effectiveness of the strengthening project, field load tests are conducted. The results show that the static and dynamic performance of different span box girders is better than that before strengthening. Through the strengthening process described in this paper, the stiffness of the structure is improved by strengthening.