Surface Fitting Method For Extracting Rotational Ground Motions And Multi-Dimensional Structural Seismic Responses Analysis

Seismic ground motion essentially is a type of temporal and spatial motion of ground caused by seismic waves.Spatial nature refers its motion at different points along different directions on the surface varies with each other.Extending to earthquake engineering,this feature becomes the non-uniformity and multidimensionality of seismic excitations.The study on rotational components is lagged due to the slow development of related theories and observation technologies,which leads to the consideration of the non-uniformity and multidimensionality of seismic excitation in seismic design is basically limited in translational components.While seismological researches have confirmed the existence of rotational ground motions,and massive field investigations and simulations have revealed that they can be devastating for the structures of large dimension,high height or sensitiveness to high frequency contents.For a more comprehensive understanding of earthquake,rotational ground motions should be seriously considered and systematically studied in order to improve the safety of high-rise building,transmission tower,large high-speed railway station,sea crossing bridges and nuclear power plants.The main contents and conclusions are as following:(1)Domestic and international researches on rotational ground motions and their impact on structures are sorted out and three main aspects are focused:the theoretic methods of rotational components estimation;new developments of rotational seismometers and the impacts of rotational components to high-rise buildings and large span spatial structures.Two problems are issued:how to estimate reasonable rotational ground motion components for practical engineering and the joint effects of translational excitations and rotational excitations for the seismic response of high-rise buildings and large span spatial structures.(2)A method named Surface Fitting Method(SFM)to extract rotational components at any point on the array area and around any two perpendicular horizontal directions and the vertical direction from the displacement field recorded by dense arrays is proposed.Detailed explanation and deduction process of SFM are provided.The comprehensive comparison study between SFM rotations and recorded rotations and GM rotations(Geodetic Method,which is the most accepted method in dense array derived rotations)reveals that SFM can produce rotations much closer to actual recordings and can be used in seismic analysis.(3)A double-check percedure is proposed to check the uniformity and usability of the recordings from dense arrays in data preprocessing.A parameter named normalized root mean square velocity(N-RMS-V)is defined to describe the uniformity and usability of recordings.Recordings not suitable for this research are selected and deleted.Meanwhile,a parameter named root mean square fitting error(RMS-error)is defined to show the fitting errors of line,parabola and arc fittings and find that the ground surface of arrays in this research is close to a parabolid during earthquake.(4)Based on SFM rotational components,time history analyses of high-rise buildings(taking a transmission tower as example)under multidimensional seismic excitations and large span spatial structures(LSSSs)(taking Dalian International Conference Center as example,DICC)under multi-support and multi-dimensional sesmic excitations are realized.For transmission tower,results reveal that rocking components can considerably increase the top displacements and torsion component can enomornusly increase the moment reactions at the base,especially the torque.Addtionally,the internal forces of the elements at the transform part between the tower body and tower head also undergo a sharp rise for both rocking and torsion components.For high-rise buildings,which are taken as an only rocking sensitive structures,both the rockings and torsion should be considered simultaneously.For DICC,results show that non-unifomity and multidimensionality of excitations both enlarge the overall torsion response of different parts.The overturning moments are also increased as well as the internal forces of the columns redistribute to the periphery of the foundation.A phenomenon is observed that when excitations are input uniformly,the influence of rotational components to structural response is small,while for multi-support input,the influence of rotational components is large.This reveals that for LSSSs,non-unifomity and multidimensionality of seismic excitations are connected,so a comprehensive response analysis requires simultaneous consideration of nonunifomity and multidimensionality.