City construction is strengthened

foundation soil structure and properties change

and the predominant period and the vibration property of foundation soil alter in city region. If ground soil predominant period and structure natural period are close to each other

they can produce resonance destruction

resulting in many unusual phenomena that can not be explained with universal knowledge in the earthquake. Structure natural period is usually "definite value"

but predominant period which may be "variable" is often neglected. The main reason of predominant period change comes from the effect of geological body or the site soil and the changes of border condition. Many aspects of urban construction

such as development of the underground space of large yardstick in the city

establishment of a large number of piles

especially even overlength piles

the enclose and protect of large deep foundation pit

application of deep and big foundation

reinforcement and treatment of the weak soil ground

the drawing and polluting of groundwater

the additional stress of the geological body induced by; topographical change and city unique environmental effect etc.; will change the structure of site soil and the properties of foundation soil; accordingly change the classification of the place partially or wholly

will influence the characteristics of the covering soil layer and the parameters like shear wave velocity; consequently the predominant period of foundation soil will change. Therefore

in aseismic design it is necessary to comprehensively consider the effect of the variation of site category which changes with site boundary conditions before and after construction

on the aseismic features of buildings.