Analysis Of Hysteresis Parameters And Seismic Performance Of Coastal Corrosion Structure

A large number of urban agglomerations are distributed along the coast of China,The coastal zone has been in the atmospheric environment eroded by chloride ion and earthquake prone areafor a long time.With the explosive growth of urban construction in our country,there are more and more RC frame structures in coastal urban agglomeration.It is necessary to study the durability and seismic performanceof RC frame structure.The key problem of RC frame structure durability is the nonlinear degradation of structure under seismic load and the degradation of material properties with service time.The key study of its seismic performance is to select a numerical model which can describe the nonlinear degradation of concrete.Therefore,this topic systematically and deeply studies the durability of coastal structures for RC frame structure.The seismic time-varying vulnerability analysis method is adopted for RC frame structure.The main work and conclusions are as follows:1)Under strong dynamic load,RC structure begins nonlinear deformation stage,such as yield and cracking.The degradation behavior is usually simulated by polygonal hysteretic model and smooth hysteretic model.The polygonal hysteretic model belongs to the simplified model with serious loss of analysis accuracy,while the smooth hysteretic model belongs to the mathematical model.The more complex nonlinear degradation behavior can be simulated by expanding the smooth hysteretic model parameters.BWBN smooth hysteretic model is used to describe multiple degradation behaviors of concrete through the differential equation of smooth change in each step.Newmark-β and Runge-Kutta method are used to solve the model equations.Runge-Kutta method is solved by converting high-order differential equations into low-order differential equations,it can be solved directly by calling the functions in Matlab toolbox,which is recommended.The two methods mutual verify the correctness of the numerical solution.2)The multi-parameter smooth hysteretic model can better simulate the complex nonlinear degradation behavior of structures,the primary problem of the application of BWBN model is parameter identification,and there are redundant parameters in multiple parameters of BWBN model.The insensitive parameters can be locked by using the methods of at one time sensitivity and global sensitivity for improving the identification efficiency.The complex degradation behavior of concrete is difficult to obtain satisfactory identification results with a single objective function,the multi-objective NSGA-Ⅱ genetic algorithm is used for parameter identification.The multi-objective function of displacement and the multi-objective function of restoring force are proposed respectively.Based on the recognition results of genetic algorithm,when the number of recognition samples reaches a certain number,the deep learning neural network model can be constructed,and the parameter recognition is transformed into multiple vector regression problem.The proposed deep learning algorithm is simple and fast.3)In coastal service environment,the reinforcement gradually rusts and degenerates with chloride ion corrosion.Probabilistic corrosion degradation model is used in RC frame durability model.The duracrete probability model based on Fick’s second theorem is adopted for chloride ion erosion,which considers the probability distribution form of multiple influencing factors.Due to the pulse effect of reinforcement corrosion rate,a hybrid distribution model is proposed to calculate the reinforcement corrosion rate,which can ideally calculate the corrosion rate of reinforcement in different periods.Based on the corrosion rate of reinforcement,the material degradation law of reinforcement in different service periods is calculated.4)The beam column joints of the finite element model in seismic analysis are simulated by BWBN model,the degradation of materials in service period is defined by hybrid probability model,and the time-varying finite element model of RC hysteretic frame is established.Based on the incremental dynamic analysis method,the seismic vulnerability analysis is carried out.and two damage indexes,the maximum interlayer displacement angle and the maximum residual displacement angle,are considered.Compared with the analysis results of cast-in-place frame,it is found that hysteretic frame has small residual displacement angle and seismic failure probability,which shows that hysteretic frame plays a good role in energy dissipation.The seismic failure probability of hysteretic frames gradually inclines to the left in different service periods,indicating that the seismic failure probability of hysteretic frames increases with the increase of service period.5)Earthquakes are often accompanied by aftershocks of different intensities.RC structures often have certain damage after the main earthquake,and the damage of RC structures will be further deepened when the aftershock occurs.By real-time adjusting the model parameters of hysteretic frames in different service periods,the damage degradation characteristics of structures can be captured.Through the time-varying vulnerability analysis of hysteretic frames under the action of main shock and main aftershock,it can be observed that the structural failure probability under the action of main aftershock is greater than that under the action of main shock.In order to quantitatively analyze the impact of main aftershocks,the seismic economic loss of the structure is evaluated based on time-varying vulnerability analysis.The results show that the economic loss of the structure under the action of main aftershocks is much greater than that under the action of main shocks.