| In recent years, the mountain structures have been developed increasely in mountainous cities, step-terrace structure as the most typical one among them gets widely used. The biggest difference between step-terrace structure and regular structures is that step-terrace structure have two ground planes, which results in irregular lateral stiffness seriously and sudden changes of bearing capacity in storey, likewise, the mechanical behaviors will differ from regular structures'. These problem forementioned will make the design process more difficult. So far there are not so much research of step-terrace structure domesticly, the process of engineering practice still lack relative guidance of code. Therefore, conducting a research of step-terrace structure' s seismic performance is necessary and urgent.This paper uses PERFORM 3D to establish an finite element analysis model of step-terrace structure in 3D space at antiseismic districts against degree 8(0.2g) earthquake, exploring the response of dampers which are set in horizontal or vertical positions of the step-terrace structure, identifying the optimized position of dampers. Besides, this paper also uses the Incremental Dynamic Analysis(IDA) to research the storey drift angle, roof displacement and base shear of uncontrolled structures, optimized structures and covered structures, focusing on the change regularities under increasing seismic dynamic strength. Then the paper makes a relevant evaluation by using IDA and Collapse Margin Ratio(CMR) is introduced to evaluate the structural anti-collapse capacity.Through the research, main conclusions of this paper are listed as follows:(1)When determining the reasonable vertical arrangement of dampers in the structure by using the Sequential Search Algorithm(SSA), it's more appropriate to choose weighted combination with multi-control indexes as the objective function. By doing so, the harmful effect of the step-terrace structure's high order vibration mode and grounding form will be reduced and the locally optimal phenomenon will be avoided.(2)When determining the reasonable horizontal arrangement of dampers in the structure, dampers are better to be set symmetrically along the structure's longitudinal direction. By doing so, the overall response of the structure will be reduced effectively and the torsion effect won't be amplified. In the structure's transverse direction, when the damper is arranged, it is advisable to choose the damping eccentricity to tend to the flexible end of the structure, and the damping eccentricity should not be too large.(3)For dampers selection, there is an optimal damping index and damping coefficient, although they cannot make all the structure response reached the minimum, the damping efficiency is the highest.(4)Under the same ground motion intensity, the response of the controlled structures is less than that of the uncontrolled structure, the elastic stage of controlled structures is longer than that of the uncontrolled structure; In the structure's longitudinal direction, the controlled structures can delay the damage of the upper ground columns and increase the deformation capacity of the structures; In the structure's transverse direction, the optimized structure can reduce the torsion effect of the structure, though the covered structure reduces the torsion effect of the structure limitedly, it arranges lots of dampers that can dissipate a large amount of seismic energy and reduce the response of it. By comparing the discrete properties of IDA curves of three kinds of structures, it can be known that the discrete properties of Sa are smaller than that of PGA as the IM parameter under different DM parameters.(5) Based on the 50 percent quantile curve, the OP, IO, LS and CP four performance points of the structure are determined. The performance points in the two directions of the controlled structures have a greater degree of improvement than that of the uncontrolled structure. Because of the effect of torsion effect, the uncontrolled structure and the covered structure will quickly enter the IO phase from OP phase.(6)Comparing the fragility curves of three kinds of structures shows that the exceedance probability under different performance levels in two directions of the controlled structure is significantly lower than that of the uncontrolled structure; In the structure's longitudinal direction, the uncontrolled structure basically meets "Undamaged under Minor Earthquake", the controlled structure meets "Elasticity under Moderate Earthquake"; In the structure's transverse direction, the uncontrolled structure meets " Elasticity under Minor Earthquake", the optimized structure meets " Elasticity under Minor Earthquake", the covered structure meets " Elasticity under Strong Earthquake ".(7) Two directions of three kinds of structures meet the requirement of "No Collapsing in the Strong Earthquake". By introducing Collapse Margin Ratio(CMR), proving that the anti-collapse ability of the controlled structure is better than that of the uncontrolled structure. The effect of optimized structure is slightly worse than that of covered structure, but the economy of optimized structure is obviously better than that of covered structure.With gradually paying attention to the mountain building structure in recent years, more and more research has been carried out. However, the research on the frame structure with the addition of dampers is very little. This paper aims to study step-terrace frame structure with energy dissipation, deepen the understanding of step-terrace structure further. This paper mainly has the following innovative points:(1)Fluid viscous dampers which are optimized arrangement in two spindles and vertical directions of step-terrace frame structure are studied.(2)By IDA method, drawing the IDA curves of uncontrolled structure, optimized structure and covered structure.(3)Draw the fragility curves of uncontrolled structure, optimized structure and covered structure. |
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