| The mountainous area accounts for more than half of the land area in china,Especially in Chongqing and Sichuan,In order to use land resources more effectively,there are more and more mountain building structure,among which the step-terrace structure accounts for a large proportion,Because of the difference in the elevation at the bottom of the layer structure,and its mechanical performance is significantly different from that of ordinary frame structure.China is an earthquake-prone country,There are many seismic zones and faults in China,and many cities are located near the faults,Therefore,more and more scholars pay attention to the characteristics of near-fault earthquake.because near-fault site ground motions include pulse signals,the structure damages are much greater than non-pulse ground motions.According to the data of seismic,it shows that after a major earthquake will be accompanied by aftershocks,or even strong aftershocks.Therefore,it is necessary to consider the influence of the near-fault aftershocks on the step-terrace structure.In this paper,the seismic performance and damage assessment of the step-terrace structure under the near-fault mainshock-aftershock sequences are studied.The main work and conclusions are as follows:(1)Through the contrastive analysis of numerical simulation result and measured data from the quasi-static test of the step-terrace structure by Chongqing University Structural Laboratory which proves the accuracy of Opensees finite element model.(2)Three step-terrace structure with Seven-layer and an ordinary flat frame structure are designed with reference to the current norms of China,according to the five structural response indexes: the damage index,the energy dissipation,the distribution of plastic hinge,the maximum interlaminar displacement angle,the maximum shear force of the upper strata.The seismic performance of structures was analyzed under the near-fault mainshock-aftershock sequences and the far-fault mainshock-aftershock sequences.Because of step-terrace structure shows obvious irregularity in the vertical direction,the damage index,energy consumption and development degree of plastic hinge in the upper-ground are greater than other floors,the flat structure floors with higher energy consumption and severe plastic hinge development are mainly on the 1-3 floors,the damage and energy consumption of lower floor of step-terrace structure are obviously smaller than that of corresponding floors of flat structure,and the damage and energy consumption of higher floor of step-terrace structure are obviously greater than that of corresponding floors of flat structure.Damage index and energy consumption indicators can better reflect the influence of aftershocks than the others,and the response indexes of the structures under the near-fault mainshock-aftershock sequences are greater than those under the far-fault mainshock-aftershock sequences.(3)The incremental dynamic analysis method is used to analyze the energy dissipation mechanism and the energy dissipation growth law of step-terrace frame structure under the near-fault mainshock-aftershock sequences and the far-fault mainshock-aftershock sequences from the energy dissipation of beams,columns,total energy and the energy dissipation of each layer.The results show that when the main and aftershocks intensity increase gradually,the increase of energy consumption of beams and columns increases,And the increase of energy consumption of columns is larger than that of beams.When the main and aftershocks intensity increase gradually,the ratio of energy consumption of beams to total energy consumption of structures decreases gradually,and the ratio of beam energy consumption of flat structure is larger than that of step-terrace frame structure under the same earthquake condition.The increase in energy dissipation of beam and column and the increase in total energy dissipation under the near-fault mainshock-aftershock sequences are greater than the increase under the far-fault mainshock-aftershock sequences of same PGA,and the ratio of beam energy consumption under the near-fault mainshock-aftershock sequences is less than that of the far-fault mainshock-aftershock sequences of same PGA.When the PGA of the main shock remains unchanged,as the increase of the aftershock intensity(),The ratio of the energy consumption of the upper ground layer to the total energy consumption of the structure gradually increases.With the increase of the PGA of the main and aftershocks,The ratio of column energy consumption to beam energy consumption increases gradually in the upper ground layer of step-terrace structure.The ratio of the energy consumption of the upper ground layer and the ratio of the energy consumption of the upper ground column to the energy consumption of the beam under the far-fault mainshock-aftershock sequences are greater than that under far-fault mainshock-aftershock sequences.(4)The damage index of the upper ground layer of the step-terrace structure is the largest under the mainshock-aftershock sequences,and the additional impact of aftershocks on the damage index of the upper ground layer is greater than other floors,The additional effect of near-fault pulse-like aftershocks on the damage index of the ground layer and the bottom of the flat structure is more significant than that of far-fault non-pulse aftershocks.With the increase of the PGA of the main and aftershocks,The damage index of each structure increases gradually,under the same earthquake condition,The damage index of step-terrace structure is higher than that of flat structure,The damage index of the structures under the near-fault pulse-like aftershocks is greater than the far-fault non-pulse-like aftershocks,the increment of the damage index of the step-terrace structure under the near-fault pulse-like aftershocks is greater than that of flat strycyure under the far-fault non-pulse-like aftershocks,and the increment of the damage index of the structure under the near-fault pulse-like aftershocks is greater than that under the far-fault non-pulse-like aftershocks. |
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