Research On Shock Absorption Performance Of Double-layer Isolation System Under Near-fault Ground Motion

Earthquakes are a serious and common natural disaster.Near-fault earthquakes are the most complex earthquakes with ground motions and are extremely destructive.However,at present,there are few studies on near-fault earthquakes in China compared with far-field earthquakes.In this paper,we mainly study the effect of rupture forward directivity,fling step effect,velocityless pulse,hanging wall/footwall effects on the double-layer isolation system under the near-fault earthquake.The main research conclusions are as follows:(1)The modal analysis of the high-rise regular frame structure shows that the period ratio of the three-layer isolation system is the smallest.For regular structures,under the effect of frequent earthquakes and forward rupture directivity effect,the three-layer isolation system has the best effect on controlling the elastic interstory drift angle and roof acceleration.Under rare earthquakes,the elastic interstory drift angle of the third layer is greater than the six layer isolation Earthquake system.Under the action of frequent earthquakes and fling step effect,the interstory shear force of the three-layer isolation is the smallest,and the elastic interstory drift angle is greater than that of the six-layer isolation in the third,fourth,and fifth layers.Under rare earthquakes,the three-story isolation system has the best isolation effect under the action of fling step effect.Under frequent earthquakes and velocityless pulse,the seismic response of the three-layer isolation system is the smallest.In a rare earthquake,the elastic interstory drift angle of the third layer is greater than that of the six-layer isolation system.Under the effect of the hanging wall/footwall effects,the three-layer isolation system can best weaken the interstory shear force of the structure.The elastic interstory drift angle from three to five layers are greater than the six-layer isolation,and the roof acceleration of the three-layer isolation system It is slightly smaller than the six-layer isolation.Therefore,it is recommended that when high-rise buildings use double-layer isolation system,the middle isolation layer should be arranged in the lower middle position.Comparing the seismic response of the hanging wall/footwall effects,it is found that the seismic response caused by the footwall effects is greater than the hanging wall effects.Under rare earthquakes,the ratio of the seismic response caused by the hanging wall effects of the double-layer isolation system to the footwall effects is less than that of the frequent earthquakes.The ratio of the base isolation and the basic fixed model is almost unchanged.It can be observed that the influence of the footwall effect on the structure is related to the self-vibration period of the structure.The larger the self-vibration period is,the larger the interstory shear force andelastic interstory drift angle caused by the footwall effect is compared with that caused by the hanging wall effects.(2)For plane irregular structures,under the effect of frequent earthquakes and forward rupture directivity effect,the interstory shear force of the three-layer isolation system is the smallest,and the elastic interstory drift angle of the third and fourth layers is greater than that of the six-layer isolation system The acceleration of the roof acceleration of the three-layer isolation system is the smallest.In the case of frequent earthquakes,the interstory shear force of the three-layer isolation system is the smallest under the action of the fling step effect,and the elastic interstory drift angle between the three to five layers is greater than that of the six-layer isolation system.Under the action of rare earthquakes and fling step effect,the three-layer isolation and the six-layer isolation have poor control effect on the elastic interstory drift angle and interstory shear force,and the abrupt change value of the interstory shear force is greater than the fixed foundation model.In the case of frequent earthquakes and velocityless pulse,the isolation effect of the three-layer isolation system is the best,but the third-layer isolation elastic interstory drift angle of the three-layer isolation system under the rare earthquake is greater than the six-layer isolation.The displacement ratio of the Y-direction of the foundation fixed structure is greater than 1.2 in six layers or more,exceeding the specification limit,and the displacement ratios of other structures all meet the specification requirements.The X-direction torsional displacement ratio of the structure becomes larger at the middle interval seismic layer,and the Y-direction displacement ratio becomes smaller at the intermediate interval seismic layer.The displacement ratio of the Y-direction of the foundation fixed structure is greater than 1.2 in six layers or more,exceeding the specification limit,and the displacement ratios of other structures all meet the specification requirements.The X-direction torsional displacement ratio of the structure becomes larger at the middle segregation layer,and the Y-direction displacement ratio becomes smaller at the middle segregation layer.The six-layer isolation system has the best effect on controlling the structural displacement ratio.Therefore,the middle segregation layer can be arranged in the lower middle position to have a good isolation effect.Comparing the seismic response of irregular structures under large and small eccentricity,it can be seen that the large eccentricity of the isolation layer will not greatly affect the torsional performance of the planar irregular structure within a certain range,but will increase the horizontal displacement of the isolation support.In the X direction,the displacement ratio of the large eccentric structure is larger than that of the small eccentric structure,and in the Y direction,the displacement ratio of the large eccentric structure is smaller than that of the small eccentric structure.It can be seen that the eccentricity of the isolation layer and the torsional performance of the structure may not be a simple linear relationship.Whether the 3% eccentricity is applicable to near-fault earthquakes needs further study.