Research On The Reinforcing Effect Monitoring Of Concrete Bridges Strengthened With Pretressed CFRP Plates

Rapid bridge strengthening method with prestressed CFRP plates is one type of new bridge strengthening technologys developed in recent years. However, it is lack of effective monitoring and evaluation methods for the prestressed loss of the prestressed CFRP plates currently. For this situation, this paper firstly uses the long gauge FBG sensing technology to monitor the prestressed loss. Moreover, the mechanical properties of prestressed CFRP plates and concrete and the characteristics of prestressed loss of CFRP plates are also studied through a series of experiments and finite element analysis. Accordingly, the corresponding monitoring and evaluation methods are proposed for the prestressed loss of the prestressed CFRP plate. Finally, the strengthening effectiveness of Xinshu River Bridge with prestressed CFRP plates is monitored and and evaluated through long-term monitoring prestressed losses of Prestressed CFRP plates and finite element modeling.The main contents and conclusions are as follows:(1) Through the theoretical study on the prestressed loss of the prestressed CFRP plates and concrete stress in tension and compression zones during the strengthening process and operation periods, the main reasons for the prestressed loss is analyzed and the corresponding formula of prestressed loss are established. Meanwhile, the maximum tensile and compressive stresses formulas are established as well during the strengthening process and operation periods.(2) A series of experiments are carried to study the strengthening effects and prestress loss of the prestressed CFRP plates. The distributed long gauge FBG sensors are used to monitor the strain changes of CFRP plate, concrete and rebar and the prestressed loss of CFRP plate in a real time. The results show that the prestressed loss gradually stabilizes and is less than 5% in 50 days. It is revealed that the prestressed CFRP plates work together with concrete beams and meet expected design requirements. Furthermore, ANSYS model is established to analyze the strengthened beams. The results show that the strain changes of each part agree well with the measured ones during the tension process, which indicates that the strengthening effect can meet the design requirements. According to studying on beams strengthened with relacart anchoring system and rigid self-locking anchoring system respectively, the results show that the beams with the relacart anchoring system meet better expected effect. At the same time, through carrying out the four-point bending static and fatigue test, the results show that the prestressed CFRP plates have good strengthening effect, and initial cracking load and bearing capacity of concrete increased by 60% and 30% respectively. It’s also indicated that two anchoring systems have good anti-fatigue performance.(3) Using long gauge FBG sensors to monitor Xinshu River bridge with prestressed CFRP plate, real-time strain changes of concrete and CFRP plates are monitoried as well as long-term strain loss of prestressed CFRP plates. The results show that the max compressive stress of concrete in box girder across increment is about 0.42 MPa within the range of the finite element calculation of 0.25-0.60 MPa; the strain of the CFRP plates reaches about 7500με after the tension process. It is revealed that short-term prestressed loss is about 3% of the tensile stress and meets the design requirement; According to monitoring the long-term strain changes of prestressed CFRP plate, the long-term prestressed loss rate of prestressed CFRP plate is about 5%. And over time, the prestressed loss rate gradually decreases and has no longer changes after 3 months. In conclusion, it’s showed that strengthening technology with prestressed CFRP plates has good strengthening effect in actual bridge strengthening engineering.