Prestressed concrete continuous girders, developed in the 1940s and 1950s, have frequently been used in bridge construction because of the ease of construction (using materials fabricated off-site) and lower cost (compared with steel and reinforced concrete). While continuous girders have performed well, cracks can appear in the concrete over time, exposing the embedded metal to corrosion, and threatening the safety of the bridge. In addition, increases in the volume of traffic and heavy-duty vehicles have put more stress on these bridges, particularly those built early on. It is important to monitor the health of these bridges and perform strengthening repairs when necessary.

While there are many common strengthening methods, researchers Kexin Zhang, Tianyu Qi, Dachao Li, Xinfeng Liu, Xingwei Xue, and Fayue Wu wanted to study external prestressed reinforcement, which they hoped would improve the bending strength and stiffness of prestressed concrete. 

They used a 25-year-old bridge in Qiqihar City, China, for testing. Their findings published in the Journal of Performance of Constructed Facilities, “Health Monitoring–Based Assessment of Continuous Girder Bridge Reinforcement,” include results of the construction process monitoring, static load testing, and health monitoring after reinforcement. Their paper is available in the ASCE Library at The abstract is below.


This paper introduces a method of strengthening prestressed concrete continuous box-girder bridges with prestressed steel strands. Construction process monitoring, field load tests before and after reinforcement, and health monitoring after reinforcement were performed to verify the effectiveness of the external prestressed steel strand reinforcement method. During the construction monitoring process, the measured values of each tensioning step are basically consistent with the theoretical values, but the measured values are slightly less than the theoretical values. The results of the field load tests show that the bending strength and stiffness of the strengthened girder have been improved. During health monitoring, the strain value and deflection value data for some parts across the specified section were collected. According to the data, the strain and deflection values fluctuated within the specified limit, and the bridge was always in a safe state.

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