Reseach On Concrete Crack Identification Method Based On Brillouin Gain Spectrum

Reinforced concrete structures have been widely used in various fields of engineering construction,but in the long-term use process,concrete structures will inevitably produce cracks,and the continuous expansion of cracks will seriously affect the safe use of the structure.Many concrete crack monitoring methods have been developed today,but most of them are based on point sensors,which have the disadvantages that it is difficult to comprehensively cover the structure and the monitoring effect is not ideal.At the same time,due to the randomness of the occurrence of structural cracks,traditional point sensors cannot effectively capture crack information,resulting in hidden safety hazards in the structure.Therefore,it is urgent to develop a technology that can comprehensively sense the crack information of concrete structures.This paper presents a method for identifying concrete cracks based on the distributed fiber Brillouin gain spectrum,using high-performance differential pulse pair-Brillouin optical time domain analysis(DPP-BOTDA)technology to monitor the occurrence and expansion of concrete cracks at various stages.The method was systematically studied and verified by the static load test of reinforced concrete beams.The details are as follows:1.A finite element numerical simulation study of crack monitoring of distributed fiber-optic concrete beams was carried out.First,a finite element analysis software was used to establish a simple reinforced concrete beam model.The loading method of four-point bending was used to study the information on the change of the strain field at the preset crack position of the pure bend in the middle of the beam with the load.Influence of elastic modulus and other factors on strain transfer efficiency.2.Through numerical simulation analysis,the three-wave coupling effect of pump light,continuous light and fiber strain field based on DPP-BOTDA principle was studied.Based on the working principle of DPP-BOTDA,a MATLAB program was compiled to realize the three-wave coupling of the strain field of the fiber at the crack position obtained from the finite element simulation analysis of the pump pulse light,continuous light,and analysis.The strain field around the crack with different resolutions and different loads was obtained Brillouin Gain Spectrum Variation Characteristics.3.A concrete crack identification method based on Brillouin gain spectrum was established.Combining the analysis results of finite element simulation and numerical simulation,a concrete crack identification method based on the characteristics of Brillouin gain spectrum characteristic parameters is obtained,so as to realize timely early warning of crack occurrence and expansion at various stages.4.A crack monitoring test for distributed fiber-optic concrete beams was carried out.Reinforced concrete beams are processed and manufactured.By laying distributed optical fibers on the bottom of the beams,DPP-BOTDA technology is used to monitor crack growth during loading of the concrete beams.The Brillouin gain spectrum data collected is extracted and the established identification method is performed verification.