Theoretical Solution To The Change Of The Site Predominant Period Caused By Soil Softending

Many of earthquake damages are caused by the resonance between thesite (foundation) and structures, or due to class resonance effect, shown in lotsof earthquake damage survey data. The most of damages to high-rises on thesoft land, far-field brick chimney and other highly flexible structures are dueto that. The earthquake damage of the longer period structure is moreseriously on the soft soil area, and which of the short period structure is moreseriously on the hard site.The site predominant period is the period when the venue vibration mayappear the maximum amplitude, is one of the most important dynamiccharacteristics of the site, is the basis of the site classification. In the seismicdesign, the study on site predominant period is particularly important, in orderto make the natural period of the structure is different from it.According to a large amount of seismic records of the liquefied ground,the long-period components of seismic wave are amplified, that is to say, thesite predominant period become bigger due to the liquefaction. The saturatedsand and the cohesive soil which contains a number of cohesive particleswould be softened under the dynamic loads such as the earthquake load,whose dynamic shear modulus would decrease, the fundamental period wouldchange.In this thesis, in order to acquire the solution to the site predominantperiod, the actual horizontal site is simplified into one-particle system,two-particle system and three-particle system. The comparison with theexisting other methods is conducted, and the theoretical solution to the changeof site predominant period caused by softening is got. The influence isanalyzed, which caused by the softened layer and softened extent on the sitepredominant period.The main work can be outlined:1. The predominant period of the site covered by homogeneoussingle-layer is acquired through the fluctuation method and the one-particlesystem method, the comparison of the two methods is conducted.2. The site predominant period is gained through the two-particle systemmethod, and the comparison with the exact solution is analyzed. Thetheoretical solution to the change of site predominant period caused bysoftening is got through the two-particle system method, when the sitecontains weak layer.3. The site predominant period is gained through the three-particlesystem method, and the comparison with the exact solution is analyzed. The theoretical solution to the change of site predominant period caused bysoftening is got through the three-particle system method, when the sitecontains weak layer.4. Taking advantage of the two-particle system method and three-particlesystem method, the influence which caused by the softened layer and softenedextent on the site predominant period is analyzed.