Seismic Vulnerability Analysis Of RC Frame Structures In Offshore Environment And Resilience Assessment

Our country has a vast territory and long coastline.Reinforced concrete structures in coastal areas will be eroded by chlorine salts and so on.With the increasing service age of structures,the structural performance of RC frame structures will deteriorate.Therefore,it is of great significance to evaluate the seismic performance of multi-age reinforced concrete frame structures in order to ensure the seismic reliability of structures in offshore environment.In this paper,several reinforced concrete frame structures with different height and fortification intensity under offshore environmental conditions are taken as the research object,and the effects of different service age,fortification intensity,storey height and axial compression ratio are considered.The real sea ground motion is taken as the input ground motion,and the peak ground motion acceleration(PGA)is taken as the index of ground motion intensity.Using the maximum interstory displacement Angle as the boundary index of structural performance and failure state,the time-varying seismic vulnerability analysis of RC frame structures in offshore environment is carried out,and the seismic vulnerability curves of RC frame structures with different layers and different fortification-intensity are obtained.By introducing the time variable,the time-varying seismic vulnerability surfaces of different earthquake intensities and different service ages are obtained.According to the Seismic Toughness Evaluation Standard of Buildings,the seismic toughness evaluation of RC frame structures under different service ages in offshore environment is carried out.The main research contents of this paper are as follows:(1)Determination of constitutive model of reinforced concrete materialBased on the existing research at home and abroad,a fine reinforced concrete material constitutive model is determined based on Open SEES finite element software.In the constitutive model of concrete material,the influence of carbonization on the constitutive model of concrete under different service ages is considered,and the decline of seismic performance of concrete with service ages is considered by dividing the concrete core zone and non-core zone.In the constitutive model of reinforcement material,the corrosion of reinforcement by chloride ions is considered,and the diffusion process of chloride ions is divided into sections.The initial corrosion time,diffusion coefficient of chloride ions and corrosion rate of reinforcement are determined.Based on the deterioration mechanism of concrete and reinforcement materials,a deterioration model of material properties was established.(2)Establish the RC frame structure refinement analysis model in offshore environmentTaking fortification intensity,layers and axial compression ratio as the main control parameters,a typical RC frame structure in offshore environment is established.Based on the degradation mechanism of material properties,finite element analysis model of RC frame structures considering material properties degradation is established by using finite element software Open SEES.The mechanical properties of the reinforced concrete column under horizontal reciprocating load were analyzed,and the seismic properties of the reinforced concrete column were compared with those of the reinforced concrete column considering the influence of corrosion.The natural vibration characteristics of the finite element analysis model and the structural response under frequent earthquakes were compared by different software to verify the accuracy of the numerical analysis model.(3)Seismic vulnerability analysis of RC frame structure in offshore environmentBased on the incremental dynamic analysis method(IDA),the seismic response analysis of RC frame structures in offshore environment is carried out,and the probabilistic seismic demand model is established.Combined with the analytical seismic vulnerability model,the seismic vulnerability curves of RC frame structures with different ground motion intensities and different service ages are obtained.By comparing the seismic vulnerability curve and the median value of vulnerability,the influences of the parameters such as the number of layers,service life,fortification intensity and axial compression ratio on the ultimate state of RC frame structures are revealed.By introducing structural service time parameters,the mean value and standard deviation of vulnerability function were fitted,and the vulnerability surface of RC frame structure in offshore environment was obtained.(4)Seismic toughness assessment of RC frame structures in offshore environmentBased on the exceedance probability under different failure states obtained by the seismic vulnerability model,IDA analysis was used to obtain the loss ratio distribution,repair preparation time and repair time distribution of different models.The seismic toughness of RC frame structures was evaluated,and the functional time curve under different ground motion intensities and different service ages was drawn.Finally,the function-strength-time seismic toughness surface is obtained by interpolation.Through the toughness evaluation formula,the toughness values of different models were calculated,and the influence law of seismic toughness of RC frame structures under offshore environment was explored.