Seismic Fragility Analysis Of Multi-aged RC Frame Structures In The Offshore Atmosphere Environment

With the deepening of people’s understanding of earthquake damage and the improvement of disaster prevention awareness,the theory and calculation method of structural seismic design are becoming more and more perfect.However,the seismic analysis at this stage is mainly for newly constructed structures.In fact,the structure will inevitably suffer from environmental impact and performance degradation during service.Therefore,the evaluation of the seismic performance of RC frame structures in multiple ages is of great significance to ensure the seismic reliability of offshore environment structures.Combined with the above background,this paper is based on the performancebased seismic design concepts and methods as a guide to carry out the seismic fragility study of multi-age RC frame structures in the offshore atmospheric environment.The main research contents of the paper are as follows:(1)With stirrups corrosion rate of reinforcement,concrete strength and volume rate as the control parameter,to carry out the simulation offshore atmospheric environment after the accelerated corrosion 36 group of RC prism specimens of axial pressure performance test,the system analyzes the stirrup reinforcement corrosion ratio,concrete strength and volume ratio of peak stress,peak strain of confined concrete,the influence law of modulus of elasticity and ultimate strain;By analyzing the correspondence between the peak stress and the peak strain in corroded specimens and uncorroded specimens,the formulas for calculating the peak stress and the peak strain of concrete confined by rusted stirrup are put forward.Based on the existing model,the axial compression constitutive model of concrete with corroded stirrup is established.The reliability and rationality of the proposed model are verified by comparing with the experimental data.(2)Taking fortification intensity and number of layers as the main control parameters,17 typical RC frame structures are designed according to China’s specifications,and the structural nonlinear analysis model is built in the Open Sees.Through comparison with the test data,the rationality of the analysis model is verified.Based on the existing researches,the probability distribution of chloride diffusion coefficient and relevant parameters of steel corrosion was determined,the probability model of steel rust starting time and concrete rust swelling and cracking time was improved,and the probability model of steel corrosion rate was optimized.The sensitivity of each parameter to the model was obtained by single parameter sensitivity analysis.Then,based on the degradation mechanism of the material,the degradation model of the material property is established.(3)The Latin hypercube sampling method is used to establish the sample base of structure-ground motion analysis.Based on incremental dynamic analysis,the probabilistic seismic demand model of the structure is obtained,and combined with the analytic fragility model,the fragility curve and the failure probability matrix are obtained.In addition,the service time parameters of the structure are introduced to obtain the timevarying seismic fragility surface of the structure.Considering that the single ground motion intensity index cannot fully reflect the influence of ground motion characteristics on the structural fragility,the model of the structure fragility of the double ground motion intensity index is established,the surface of the structure fragility is drawn,and the quantitative comparison is made with the structure fragility curve of the single ground motion intensity index.