Characteristics And Modeling Of Long Period Displacement Spectra

The increasing risk of natural disasters is becoming an important threat to the sustainable development of society,economy,and environment.Earthquake disasters,especially destructive earthquakes,account for an important proportion of natural disaster losses in China.One of the most important problems in structural seismic design is the seismic input.The seismic design of long-period structures such as super high-rise buildings,long-span structures,and large liquid storage tanks is an important topic in the current seismic research.The natural vibration period of long-period structures generally reaches 6s?10s,structures of natural vibration periods longer than 10s even 15s are common in nowadays high-rise buildings,which will suffer substantial deformation or even damage under long-period ground motion.The design response spectra given in the current code for seismic design of buildings in China is only 6s,which is far from meeting the requirements of seismic design of high-rise buildings.At present,the seismic design code is mainly based on the response spectra method of bearing capacity,and the acceleration response of the structure is used to calculate the seismic action,which can not reasonably predict the maximum displacement response of a high-rise structure.The seismic design of the long-period structure needs to change from the force-based seismic design to the displacement-based seismic design.The seismic damage of structure is closely related to the displacement response of the structural system and the deformation capacity of components.Displacement-based seismic design,comparing to force-based,describes in a more explicit way the structural response and the damage,but needs reliable displacement spectra in long-periods.The simplest and most direct expression of structural displacement response estimation are the displacement response spectra,which have a clear concept and convenient engineering application.Reliable and reasonable displacement design spectra is the key element of displacement-based seismic design.Displacement spectra models have been well developed by previous researchers and been put into engineering practice and seismic design codes.However,due to the limitation of objective conditions,such as signal-to-noise ratio and the abundance of strong earthquake records,the models still have some shortcomings,which need to be modified and improved.The limitation of the existing research is mainly reflected in the limitation of the period range of the model within 6s?10s,that for longer structural periods of interest the models cannot apply.With global digital strong motion networks installation in recent decades,some exceptional platform of high-quality data to study long-period ground motion emerges.The main work of this paper is to study the characteristics and models of long-period displacement spectra based on the global high-quality strong earthquake records obtained in recent years.The main work is as follows:1.A database of strong-motion data with long period displacement spectra is established.High quality digital ground-motion data recorded in recent 45 shallow earthquakes with moment magnitude(M_w)larger than 5.5 worldwide are collected from databases,and the reliable displacement spectra in 0s?15s is given.At the same time,the moment magnitude,fault distance,site condition,and other information are provided.The database can be used to study the displacement spectra characteristics and model.At the same time,the standardized processing flow is given.2.The characteristics of the long-period displacement spectra are studied.In this paper,the influence of moment magnitude(M_w),fault distance(R_rup),and site condition(V_s30)on displacement spectra and normalized displacement spectra are studied,which provides the basis for establishing a normalized displacement spectra model in the future.3.A four-segment normalized displacement spectra model determined by 6modelling parameters is proposed,which considers only magnitude dependence.The formulae of the model parameters are given accordingly.Comparing to earthquake data,the reliability of the normalized displacement spectra model is tested.4.By comparing with the existing specifications and other scholars'research,the reliability of this model is verified.Using the collected data,ground-motion prediction equations(GMPE)of peak ground displacement(PGD)are established.With the normalized displacement spectra model and the GMPE,a displacement spectra prediction method is proposed.