Inspection, materials testing and field testing of a prestressed concrete box bridge after fire exposure

Abstract

This paper presents inspection, materials testing, field testing and parametric finite element analysis of a prestressed concrete box girder bridge after fire exposure. A detailed inspection of the fire-exposed bridge was performed through visual checking, photo examinations, and hammer detection. Samples of the concrete cores and reinforcing bars were tested; the residual strengths of the building materials (concrete, reinforcing bars and prestressed strands) were estimated. Furthermore, the temperatures at various depths were estimated. The data from field studies were used to validate finite element models. The structural behaviors of the original bridge prior to fire exposure were obtained via instrumentation from a reference bridge not exposed to fire. The static proof load test deflection results indicate that the stiffness decreased by approximately 23% after fire exposure and no longer satisfied the design requirement. The measured fundamental frequency of the fire-exposed span was approximately 97% of that of the original span and the theoretical fundamental frequency, indicating that the fire had little influence on the frequency of the concrete structure. Based on this work, the repair requirements of the bridge were determined and undertaken, and the repairs were proven to be effective via a field loading test after strengthening.