| Concrete bridge structures often affect the durability of the entire structure due to cracking,and the cracks are generated randomly in a certain area.Once the concrete bridge cracks,the resistance performance of the structure will gradually decrease,which may eventually cause the bridge to collapse and cause serious economic problems.loss.Therefore,real-time monitoring of the appearance and expansion of cracks in concrete bridge structures and the location of cracks are very necessary in the bridge structure health monitoring system.In the past,the monitoring of concrete cracks could only rely on arranging traditional sensors where the cracks may occur or manual inspections,while distributed optical fiber sensors based on optical frequency domain reflection technology can be pasted on the surface of the structure or embedded in the concrete structure to achieve all aspects of the sensor.Cover the cracks in the monitoring structure.However,whether it is surface-adhesive or embedded,strain is affected by the intermediate layer when the strain is transferred from the structure to the optical fiber.At present,there are relatively few researches on the strain transfer law of distributed optical fiber sensors.Based on the theory of distributed optical fiber strain transmission,this paper establishes a strain transmission model,analyzes the influencing factors of the strain transmission rate of distributed optical fiber sensors,and conducts two aspects of distributed optical fiber sensors based on optical frequency domain reflection technology(OFDR).Experimental research: The distributed optical fiber sensor is pasted on a beam of equal strength,and factors such as the length,width and thickness of the lower part of the glue are analyzed and researched;two different arrangements of optical fibers are pasted on the surface of the reinforced concrete beam to verify the distribution Type optical fiber sensor crack monitoring capability,paste optical fiber along the length of the beam to monitor the bending crack of the beam,paste the optical fiber along the 45-degree direction of the central axis to monitor the shear crack at the support.Based on the comprehensive analysis of the experimental results and theoretical results,the main conclusions drawn in this paper are summarized as follows:(1)Through the analysis of the strain transfer model and the derivation of the strain transfer formula,it is found that the distributed bare fiber monitoring strain has a tip effect.The four parameters of fiber bonding width,light bonding length,colloid lower thickness and colloidal shear modulus are analyzed.The results show that the improvement of strain transmission rate mainly depends on the fiber bonding length and colloidal shear modulus.(2)Equal-strength beam tests were carried out on the two parameters of optical fiber sticking length and colloidal shear modulus.The results showed that the high-shear modulus colloid should be selected when the optical fiber is used to monitor the structure matrix and the sticking length should be at least more than 20 cm To improve the strain transfer rate and achieve a good monitoring effect.(3)The concrete crack monitoring test was carried out to monitor the bending cracks and shear oblique cracks of concrete beams.The analysis of the corresponding variables,crack location,crack generation time,and cracking degree proved that OFDR technology can be accurate The location of the cracks can be used to realize the health monitoring and damage identification of the structure. |
