Study On Dynamic Damage Monitoring Of Concrete Gravity Dam Using Emi Method

Concrete gravity dam is the significant infrastructure to ensure the social production,and the safety of dam during operation service is the key issue of the construction and development of the structure.The high dams in China are mainly located in the southwest strong earthquake area.Under the earthquake load,the safety of the dam will be seriously threatened.There would be an incalculable damage to the downstream populated areas if the dams have an accident.Therefore,study on the damage monitoring and damage evaluation of concrete gravity dam under strong earthquake is crucial to our society and economic development in the significant working of disaster prevention and mitigation,which is also the key technical problem in the construction of hydraulic engineering.The seismic damage monitoring and damage evaluation of mass concrete structure based on the electro-mechanical impedance(EMI)technique and seismic measures are deeply studied to solve the critical issues and technique problems of gravity dam,some conclusions with theoretical and practical value are obtained.The major contents of this paper are concluded as follows:(1)The feasibility of applying PZT sensors to monitor the dynamic damage of concrete structure was investigated,and the evaluation index of damage degree was put forward.The damage growth of concrete specimens under impact load was analyzed numerically,and the damage volume ratio was extracted to characterize the damage of concrete beam before and after impact load.In order to quantify the effect of impact load on damage development of concrete beams,the EMI technique was used to monitor the damage of concrete beams.The relationship between the RMSD index which reflects the change of admittance signatures and the damage volume ratio was established in order to quantify the damage development of concrete beams.The results show that there is a good correlation between the RMSD index and the damage volume ratio of concrete under the impact dynamic load.(2)The feasibility of monitoring concrete gravity dam based on piezoelectric impedance technique was studied.The seismic safety performance of gravity dam was analyzed by using transient analysis,which provides a basis for damage monitoring design of concrete gravity dam.Based on the damage evaluation index of concrete beam,EMI technique was used to monitor the damage of concrete gravity dam under different earthquake conditions.RMSD based on damage volume ratio and RMSD index based on damage dissipation energy were established to quantify the conductance signals measured by piezoelectric plates to evaluate the damage degree of the dam and to predict the dynamic response performance parameters of the dam.(3)According to the vibration characteristics and failure modes of gravity dams under earthquake,an effective damage mitigation measure was put forward.The autoclaved aerated concrete(AAC)was applied to the upper part of the dam body to reduce the seismic inertia force and to reduce the earthquake energy dissipation,thus eliminating the penetrating cracks at the dam head and achieving a good seismic effect.Based on the theory of piezoelectric impedance,the damage of AAC dam under earthquake is monitored by piezoelectric sensors.The conductance signatures measured by RCC and AAC dam and the damage evaluation index were compared and analyzed,and the excellent seismic absorption effect of autoclaved aerated concrete is further explained.