Study On Seismic Response And Failure Mechanism Of Long-period Structures Based On Hilbert-Huang Transform

High-rise and high-rise buildings,isolated structures,long-span bridges and other long-term structure increase constantly,these long-period structures are basically crowded areas,seismic design is important for these long-period structures.Once Long-period structures are destroyed during an earthquake,serious economic loss and personnel casualty will be caused.However,there are some problems to be further understood and solved in the seismic design of long-period structure.Hence,it is very important to study the long-period seismic response and failure characteristics under the action of ground motion.In this paper,Based on the tool of HHT time-frequency analysis technology,The longperiod structures are studied from the aspects of transient response,structure response delay and failure mechanism.The research work accomplished by this paper is as follows:(1)A data/ extrema symmetrical extension method is proposed to decrease the end effects of HHT.Using end data symmetrical extension,the end swings result from EMD and Hilbert transform can be released to the outside of the data.Through extrema symmetrical extension,the shape of the cubic spline envelope curve is further controlled and the envelope curve of the original data is more accurate.The simulation demonstrates the effectiveness of the method.When this method is applied to the structural dynamic non-linear characteristics analysis,clear physical meaning and two non-linear mechanical characteristics including "frequency band extension" and "main frequency drift" can be described accurately.(2)A half-wavelength fitting harmonic function base on EMD method is proposed to compute the transient response and steady state response,the intrinsic mode function(IMF)through the empirical mode decomposition(EMD)of earthquake ground motion is fitted into multi-stage harmonic functions;The influence of spectrum,initial phase angle,duration,damping and so on on the transient effect is elucidated,The transient effect of long-period structure is revealed.The influence of the transient effect of longitudinal wave on the three types of ground motions,such as ordinary ground motion,near-field pulse ground motion and far-field harmonic-like ground motion,is analyzed.(3)The lag time of transient response and steady state response under harmonic loads are deduced.The factors that influence the lag time of displacement response under harmonic load are revealed.The essence of structural response lag under earthquake action is revealed.Thelaws of displacement,velocity and acceleration response lag time are clarified.The long-period structure delay laws of three types of ground motions are revealed,such as ordinary ground motion,near-field pulse ground motion and far-field harmonic-like ground motion.The relationship between the lag time of different types of ground motions and the failure modes of structures is established.The corresponding suggestions are put forward for long-period structural design.(4)The relationship between the maximum instantaneous input energy and the base shear of three structures of long,medium and short cycles is established.The method of adjusting the maximum instantaneous input energy is proposed.Comparing with the current standard method,the proposed method of "adjusting energy" is more stable,reduces repetitive seismic wave selection.Combined with the maximum instantaneous input energy and total input energy,the times of crack displacement and the times of yield displacement are introduced,the failure mode is divided into three categories: first excursion failure,mixed damage,cumulative damage failure.The three finite element structures of long,medium and short cycles demonstrate the effectiveness of the method.The dangerous types are listed in the following order: first excursion failure,mixed damage,cumulative damage failure.The short-cycle structure is prone to cumulative damage failure,and the long-period structure is prone to the first excursion failure and mixed damage.