Stress Monitoring And Safety Assessment For Long Span Prestressed Concrete Structures

Bonding protection methods and stress state monitoring of strands in prestressed concrete structures have been the main problems to be solved in the engineering sector, and ordinary strands and monitoring means can not meet the above requirements. In this paper, a new type of sensor named smart retard-bonded prestressed strand has been developed combined with the technology of smart strands and retard-bonded process, which can be directly laid on long span prestressed concrete structure to monitor its stress state replacing ordinary strands, and provide a reference for structural safety assessment as well. The main contents are as follows:Firstly, a prestress loss direct monitoring method based on tendon strain was proposed instead of complex breakdown superposition method after analysing prestress loss factors and uncertainty. Meanwhile, tendons and concrete control section’s stress, internal force and deformation were used as comparative indicators between engineering practice and theoretical design. The paper also proposed a safety assessment and early warning method by prestressed concrete structures actual working condition and safety coefficient.Secondly, ribbed smart retard-bonded prestressed strand based on Brillouin Optical Fiber or Fiber Bragg Grating (S-RPSR-OF/FBG) has been developed. Much research work has been done to obtain its properties of mechanics, bonding, friction and monitoring. The results showed that S-RPSR-OF/FBG not only inherited strong axial tensile performance and temperature and strain sensing properties of smart strand, but also added convenient and reliable retard-bonded features, which can be used to monitor prestressed state.Finally, curved and mansard S-RPSR-OF/FBGs have been applied to theater buildings to monitor stress state of long span prestressed concrete beams and plates. Impact parameters (κ、μ,θ and lf) and distributed rules and time-varying characteristics of prestress loss have been obtained. Moreover, safety assessment have been achieved after comparing measured index with design index. Meanwhile, the paper proposed some reference methods and measures for design and construction of retard-bonded prestressed concrete structures.