Seismic Damage Assessment And Fragility Analysis Of Step-terrace Frame Structure On The Slope Under The Main-after Shock

China is a mountainous and multi-hilly country.The area of mountain hills accounts for about half of the total land area.In recent years,the mountain building structure is increasing,and the step-terrace structure is the most widely used.Due to the influence of terrain height difference,there is a large difference in the elevation at the bottom of the layer structure,and there is obvious irregularity in the vertical direction.At present,the research and analysis on the structure of the step-terrace structure is not enough and the lack of normative guidance in engineering practice.At the same time,a large number of seismic data show that after a major earthquake will continue aftershocks,and even a series of strong aftershocks.But the current structure of the study does not consider the impact of aftershocks.Therefore,it is necessary to analyze the seismic performance,damage assessment and seismic vulnerability of step-terrace structure under the mainshock and aftershock.The main work and conclusions of this paper are as follows:(1)Three structures with different layers and crosses and an ordinary flat frame structure are designed with reference to the current norms of China.Combined with the maximum interlaminar displacement angle,the maximum shear force of the upper strata,the hinge rate of the rod,the energy dissipation,the damage index and so on,the seismic performance of structures was analyzed under the action of the individual vibration and the combination of the mianshock and aftershock.The results show that the influence of aftershocks on the structural response is not the same.The maximum interlaminar displacement angle,the maximum shear force of the upper strata,hinge rate of the rod can not effectively reflect the additional influence of the aftershocks.However,energy consumption indicators can better reflect the impact of aftershocks.(2)The energy dissipation mechanism of the step-terrace structure under the action of the main aftershocks is studied by using the incremental dynamic analysis method from the total energy dissipation and the energy dissipation of each layer.The results show that with the increase of the amplitude of the main and aftershocks,the total energy consumption of the step-terrace structure increases,and the ratio of the beam energy consumption to the total energy consumption decreases gradually.The percentage of energy consumption in the ground layer is the largest,and as the floor increases,the percentage of energy consumption decreases gradually.In the upper ground layer,the column energy consumption is greater than the beam energy.In the drop layer,beam energy consumption is greater than column energy consumption.With the increase of the aftershock intensity(?PGA),the energy consumption of the layers is increased in different degrees.The additional energy consumption of the upper ground layer is greatest and the additional energy dissipation of the column is greater than the additional energy dissipation of the beam.The larger of ?PGA,the greater the difference between the additional energy dissipation of the column and the additional energy dissipation of the beam.(3)Considering the additional effects of aftershocks,damage assessment of the layered structure is carried out from the additional damage index,the layer damage index and the overall damage index.The results show that the main shock is the most important factor causing structural damage.When the amplitude of the main shock is the same,with the increase of ?PGA,additional damage to the structure of aftershocks is also greater.The damage of the upper ground layer is the most serious,and with the increase of ?PGA,the additional damage index of the components of the layer structure increases,and the additional damage of the upper grounding column is the largest.(4)The Park-Ang damage index was used as the parameter of structural response,and the PGA was used as the parameter of the ground motion intensity.The vulnerability curves structure of the step-terrace structure and the ordinary flat frame structure under the main-after shock were given.The vulnerability of of the step-terrace structure and the ordinary flat frame structure is compared and analyzed.And the influence of aftershocks on the vulnerability of each structure is studied.The results show that the aftershocks increase the transcendental probability of the structure,and with the increase of the aftershock intensity,the probability of transcendence is bigger.Compared with the ground structure,the step-terrace structure is higher.And the influence of the number of layers and the number of falling spans on the vulnerability of the structure is significant.(5)The anti-collapse ability of the structure was evaluated based on the Collapse Margin Ratio(CMR),and the safety reserve of each structure was compared.The results show that,compared with the ordinary flat frame structure,the anti-collapse reserve coefficient of the step-terrace structure is small,and the anti-collapse safety reserve is lower.For the step-terrace structure,the increase in the number of layers and the number of layers will reduce the collapse of the security reserves,and the number of layers has a greater impact on CMR.