Viscoelastic Site Of Topography On Ground Motion Spectral Characteristics Of Impact Analysis

Many investigations of earthquake damages manifest that surfacetopography has significant amplification or reduction effects on groundmotion, and, therefore, it can influence the distribution of earthquakedamages directly. The purpose of studying on the influence of surfacetopography is to explain the reasons for the large amplifications andspatial variations of the ground motion and to predict some of the featuresof the ground motion during future earthquakes. So analysis of the effectof topography is one of the most important and attractive field inearthquake engineering. After a lot of investigation, we have know quite afew about the effect of surface topography on peak ground acceleration,but comparatively, the effect of surface topography on spectrum propertyof earthquake is still obscure for us. The objective of this thesis is todiscuss effects of topography on spectrum property of earthquakes,through numerical experiments and result analysis, the followingproblems are analyzed, and some applicable results are obtained.1. the choice and analysis of numerical integration methodsA numerical integration method executed in this thesis is the explicitfinite difference method suggested by Li Xiaojun et al. for analyzing theearthquake response of two-dimensional visco-elastic site. The systematicreview of this method is made in the second chapter. Besides, the virtue ofthis method is using the explicit integration formula also suggested by LiXiaojun. We know for a explicit integration formula, basic characteristicsincluding astringency,stability,precision,dissipation and overshootcharacteristic. So, as complementarity of former people's work, dissipationand overshoot characteristics of three different integration formulas arediscussed in detail. The conclusions show that the explicit integrationformula suggested by Li Xiaojun and others has stronger numericaldissipation characteristic than the other 2 formulas while the real dampingvaries from 0 to 1, and the larger the real damping is, the phenomenon ismore obvious, this kind of formula can depress or eliminate the high-frequency instability induced by Local Transmitting Boundary, and,under the condition of the same precision, this kind of formula has lesservelocity overshoot characteristic, so it is an ideal integration formula forsolving the earthquake response of complex site.2. effect analysis of topography on spectrum property of earthquakeSurface topography is complex and various, actually, effect oftopography on spectrum property refers to many factors, such ascharacteristic dimensions of topography (including height and slope angleet al.),characters of soil or rock,spectrum properties of input wavelets,angle of incidence et al. These factors can be classified into two sorts,characters of site and characters of earthquake. In order to summarizeconveniently, firstly, we discussed the difference of spectrum property ofanti-plane movement under the conditions of different topographic factorsand direction of the incident waves, then research expands to mesa andvalley. The conclusions show that the presence of topographic factors andthe direction of the incident waves not only significantly affect the peakground acceleration of site, but also affect the spectrum property of theincoming waves, and the effect of direction of the incident waves isespecially remarkable. The study also find that it is reasonable to analysespectrum properties with the input of impulse wavelets in the finiteelement simulation of wave motion.3. the effects analysis of topography on peak-acceleration andcharacteristic periodsInvestigations after earthquakes show that surface topography affectsthe peak-accleration and spectrum property of earthquake, so, it affectsthe shape of design spectra. Considerations of topographic effects in theseismic design code for buildings are suggested in form of earthquakeforce, while it is hard for engineers to get adjusting project throughseismic design code if they have to face topographic problems. In thisthesis, a model of mesa is established, a lot of artificial ground motions aregenerated and have been used as input movements, time histories of observation points are gained, finally, two methods (one is suggested byACT3-06 and another is suggested by Liao Zhenpeng and Li Dahua)areused to get the characteristic periods of sites. With these results, theeffects analysis of topography on peak-acceleration and characteristicperiods is executed and corresponding adjusting project for design spectrais suggested.