| The damage mechanism of reinforced concrete (RC) structure could be revealed by monitoring the stress process of concrete material of seismic damage. However, the feasibility and accurancy of nonlinear analysis will be directly influenced by the factors, such as the constitutive parameters of concrete materials, resistance of member sections and computional models of structures during real seismic damage status. In this dissertation, a local stress monitoring method using piezoelectric aggregate (PA) was studied and verified by experimental research and theoretical analysis in the levels of material, member, and structure, respectively. In addition, the inner stress process and distributed measurement of concrete materials, key sections of member, and important members of structure under real seismic damage status were investigated. A method of identifying the constitutive parameters of concrete material, calculating the section resistance of memebers, and updating computional models based on stress monitoring data during real seismic process was proposed. The main contents and conclusions can be drawn as following.1. The four kinds of fabrication method of PAs based on different stress condition and its seismic monitoring systems were proposed. Based on the demand of seismic stress monitoring, PAs used for monitoring compressive stress, shear stress, tri-axial stress and spatial stress were designed respectively to monitor seismic stress comprehensively. A charge amplifier was designed and a seismic stress monitoring system was established to fulfill the stress monitoring demand under the conditions of low frequency and high stress during earthquake. The seismic damage stress process monitoring system was established, and its feasibility was verified through dynamic loading tests.2. Typical PA-based concrete seismic damage stress process monitoring method was proposed. The material heterogeneity such as concrete strengths, aggregate types and maximum aggregate particle sizes, and nonlinear behavior such as loading-unloading in different stress level and monotonic loading till failure process were involved to establish the statistical relationship between the PA stress and the concrete stress by lab experiments. The analisys method for monitoring error is proposed. The suggestion number of PAs under specified monitoring error was proposed.3. The probability statisticis relationship between macroscopic and mesoscopic concrete stress based on mesoscopic FE simulation method was proposed. The numerical specimens for mesoscopic modeling were built by using RFPA2D software with the effects from the randomness of spatial distribution inside concrete and the heterogeneity of material mechanical properties considered. The parameter identification method based on mesoscopic method was proposed. This method was verified by comparing the macroscopic and mesoscopic mechanical behavior of mesoscopic model with that of test results. At the meantime, the fact that mesoscopic damage evolution of concrete can be reflected by the variation of the stress was illustrated. The key factors effect on the statistical relationship between macroscopic and mesoscopic concrete stress were studied through a number of parameter analyses.4. The feasibility analysis and measurement error of PA-based stress monitoring method used in RC compression-bending member subjected to complex stress condition were studied. Three identical RC compression-bending members subjected to cyclic loading with PAs embedded in the plastic hinge zone were fabricated and tested with the factors such as compressive-shear composite stress, effect of crack surface contact of concrete, and reinforcement constraint considerred. The flexural moment in plastic hinge zone calculated by using PA stress and reinforcement strain were compared with theoretical one. The test results showed that the stresses monitored by PAs of three RC specimens meet well with each other and can effectively reflect the progressive damage process of the concrete.The monitoring error was only about 5% at nonliear stage, showing good feasibility and accuracy of PA stress monitoring under complex stress conditions.5. The seismic damage stress process monitoring and model updating of RC strcture were conducted. A two floor RC frame shaking table test was designed and tested with the PGA of earthquake equal to 0.8g. The material properties of concrete were updated by using local stress information monitored by PA. The FE model of the RC frame was established by using OpenSEES program. The overall and local responses obtrained from FE analysis and test result respectively were compared. The results showed that the monitored stress can reflect the progressive damage process of RC structure, the model updating method based on the PA stress monitoring can significantly improve the accuracy of simulation, and the simulation error of the inter-story displacement can be reduced about 17%. Therefore, the PA stress monitoring method is very important for structural seismic damage assessment and model updating. |
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