Second Remediation of Long-Term Deflection and Cracking of PT Box-Girder Bridge Using External Post-Tensioning

Abstract

This study involves examining a second technique for improving external prestressing tendons to remediate the deflection and cracking of an 18-year-old strengthened four-span continuous post-tensioned prestressed concrete (PT) box-girder bridge. First, a forensic examination of the bridge after the first remediation is conducted. The degradation of the bridge, including vertical deflection, prestress loss, cracking, and pavement damage, is investigated. The reasons for the degradation are discussed and some recommendations are given. Then a second remediation is proposed to improve the performance of the bridge; this includes the replacement of pavement, external post-tensioning, attachment of steel plates, and sealing cracks. Finally, the service-level behavior of the beam, before and after the second remediation, was evaluated using the static and dynamic loading tests in situ. The effectiveness of the remediation on deterring deflection and cracking of the bridge is discussed. Results show that the carrying capacity, stiffness, and integrality of the bridge were improved significantly after the latest remediation. Concrete strains and vertical deflections on the tested section of the bridge decreased by about 15% and 18%, respectively, compared with that before the remediation under a similar load. The dynamic response of the remediated bridge was also improved, as indicated by the increased frequency of the vertical modes of ambient tests.