Long-term crack monitoring of prestressed concrete structures by means of distributed fiber-optic strain sensing

In the ceiling area of a connecting subway tunnel in Munich, Germany, fiber-optic sensor cables were installed for continuous long-term crack monitoring. According to the measurement concept, continuous monitoring of the total deformations as well as several reference date measurements are planned with regard to the actual crack monitoring of the prestressed concrete construction. The aim of the measurements is the fiberoptic crack monitoring of a pre-damaged prestressed concrete structure from the 1970s, which was refurbished in the course of the fiber-optic installation. The structure is exposed to high traffic loads from road traffic as well as temperature impact. The prestressed concrete structure is a single span slab construction with straight and parabolic tendons. The original ceiling had an increased potential for damage on the underside of the slab (crack pattern) as well as severe damages associated with the existing prestressing steel structure. During the renovation of the prestressed concrete slab, shotcrete with supplementary reinforcement was applied to achieve an announcement behavior in case of tendon failure. The following paper reports on the first results of crack monitoring based on continuous fiber optic measurements along the embedded fiber-optic sensing cables. The measurements are based on the technology of distributed Brillouin sensing.