The earthquake forces used in design codes of buildings should be theoretically determinable. This work examines the seismic force modification factor R based on elastic-plastic time-history earthquake analysis of SDO...The earthquake forces used in design codes of buildings should be theoretically determinable. This work examines the seismic force modification factor R based on elastic-plastic time-history earthquake analysis of SDOF systems, wherein the hys-teresis models are elastic-perfectly-plastic (EPP), elastic-linearly-hardening (ELH), shear-slipped and bilinear-elastic. The latter two models are analysed for separating the effect of the ductility and the energy-dissipating capacity. Three-hundred eighty-eight earthquake records from different site conditions are used in analysis. The ductility is taken to be 2, 3, 4, 5 and 6, with the damping ratio being 0.02, 0.035 and 0.05 respectively. The post-yield stiffness ratios 0.0, 0.1 and 0.2 are used in the analysis. The R spectra are standardized by the characteristic period of the earthquake records, which leads to a much smaller scatter in averaged numerical results. It was found that the most important factor determining R is the ductility. R increases more than linearly with ductility. The energy-dissipating capacity, damping and the post-yield stiffness are the less important factors. The energy dissipating capacity is important only for structures with short period and moderate period (0.3≤T/Tg<5.0). For EPP and ELH models, R for 0.05 damping is 10% to 15% smaller than for 0.02 damping. For EPP and ELH models, greater post-yield stiffness leads to greater R, but the influence of post-yield stiffness is obvious only when the post-yield stiffness is less than 10% of the initial stiffness. By means of statistical regression analysis the relation of the seismic force modification factor R with the natural period of the system and ductility for EPP and ELH models were established for each site and soil condition.展开更多
There are controversies on ground motion attenuation relations at the epicentral distance of about 100km. Some models predict that the seismic energy remains almost constant or becomes even stronger with increasing di...There are controversies on ground motion attenuation relations at the epicentral distance of about 100km. Some models predict that the seismic energy remains almost constant or becomes even stronger with increasing distance at this distance, while other models hold that it decreases with increased distance. The divergence lies mainly in whether SmS is stronger than direct S and surface waves at this distance. With the MsS. 9 earthquake sequence in the Yingjiang region of Yunnan Province as an example, we demonstrate that SmS is always 2 - 5 times stronger than direct S waves around the epicentral distance of 100km （which is the post-critical distance for S in this region）. Study of synthetic seismograms suggest that crustal structure has an important effect on the amplitude of post-critical SmS, with simple crust producing strong SmS. This preliminary study confirms that in China, SmS also plays an important role on ground motion at distances around 100km, which demands more studies of post-critical SmS.展开更多
文摘The earthquake forces used in design codes of buildings should be theoretically determinable. This work examines the seismic force modification factor R based on elastic-plastic time-history earthquake analysis of SDOF systems, wherein the hys-teresis models are elastic-perfectly-plastic (EPP), elastic-linearly-hardening (ELH), shear-slipped and bilinear-elastic. The latter two models are analysed for separating the effect of the ductility and the energy-dissipating capacity. Three-hundred eighty-eight earthquake records from different site conditions are used in analysis. The ductility is taken to be 2, 3, 4, 5 and 6, with the damping ratio being 0.02, 0.035 and 0.05 respectively. The post-yield stiffness ratios 0.0, 0.1 and 0.2 are used in the analysis. The R spectra are standardized by the characteristic period of the earthquake records, which leads to a much smaller scatter in averaged numerical results. It was found that the most important factor determining R is the ductility. R increases more than linearly with ductility. The energy-dissipating capacity, damping and the post-yield stiffness are the less important factors. The energy dissipating capacity is important only for structures with short period and moderate period (0.3≤T/Tg<5.0). For EPP and ELH models, R for 0.05 damping is 10% to 15% smaller than for 0.02 damping. For EPP and ELH models, greater post-yield stiffness leads to greater R, but the influence of post-yield stiffness is obvious only when the post-yield stiffness is less than 10% of the initial stiffness. By means of statistical regression analysis the relation of the seismic force modification factor R with the natural period of the system and ductility for EPP and ELH models were established for each site and soil condition.
基金sponsored by the Basic Scientific Research Specific Program (02092410),Institute of Earthquake Science,China Earthquake Administration
文摘There are controversies on ground motion attenuation relations at the epicentral distance of about 100km. Some models predict that the seismic energy remains almost constant or becomes even stronger with increasing distance at this distance, while other models hold that it decreases with increased distance. The divergence lies mainly in whether SmS is stronger than direct S and surface waves at this distance. With the MsS. 9 earthquake sequence in the Yingjiang region of Yunnan Province as an example, we demonstrate that SmS is always 2 - 5 times stronger than direct S waves around the epicentral distance of 100km （which is the post-critical distance for S in this region）. Study of synthetic seismograms suggest that crustal structure has an important effect on the amplitude of post-critical SmS, with simple crust producing strong SmS. This preliminary study confirms that in China, SmS also plays an important role on ground motion at distances around 100km, which demands more studies of post-critical SmS.
