With an objective of better understanding the nature of India\|Eurasia collision process, as manifest in the NW part of the Himalaya, gravity and GPS aided geodetic studies were carried out during the summers of 1994 ...With an objective of better understanding the nature of India\|Eurasia collision process, as manifest in the NW part of the Himalaya, gravity and GPS aided geodetic studies were carried out during the summers of 1994 through 1996. The area covered includes the Ladakh Himalaya, Indus suture zone (ISZ) and entire NW Himalaya between 74°～80° longitude and 30°～37° latitude. Gravity survey was carried out at 1～2km interval along Kiratpur—Leh—Panamik transect. Four different profiles viz., Kargil—Panikhar; Karu—Tangtse; Mahe—Sumdo and Nyoma—Kyon Tso were also taken. GPS was used, in fast\|static mode for 3\|d position determination of the gravity stations. The collected data were reduced to mean sea level using a new technique of terrain correction (Banerjee, 1998). The collected data was further combined with the published gravity data of SOI (Gulatee, 1956, Chug, 1978); ONGC (Raiverman et al., 1994) and Jin et al., 1994 to produce a new BA map for the NW Himalaya at 10mGal interval. Isostatic anomaly map of the region was also prepared using the BA map and ETOPO\|5 global elevation data set. On the IA map, an isostatic high of about 80mGal is evident over the entire course of the higher Himalaya. This elongated pattern of the gravity high aligns itself over the exposed rocks of central crystallines where the average elevation is 4500m. This 80mGal isostatic high may have been caused due to the fact that isostasy does not strictly prevail in the higher Himalaya and these are in a state of under\|compensation. This IA high has been interpreted in terms of upwarping in the Moho beneath the higher Himalaya. The IA analysis has also led to the depth of Moho to be 36～37km under the foothills, 60～65km under the higher Himalaya and 70～75km under the ISZ and beyond. Doubling of the crustal thickness is evident from the IA analysis and they are in general, in agreement with the DSS results of the Kashmir Himalaya.展开更多
New approximate formulas are proposed to determine the natural frequencies of structures considering the effects of panel zone flexibility and soil-structure interaction. Several structures with various earthquake res...New approximate formulas are proposed to determine the natural frequencies of structures considering the effects of panel zone flexibility and soil-structure interaction. Several structures with various earthquake resisting systems are idealized as prismatic cantilever flexural-shear beams. Floor masses are considered as lumped masses at each story level and masses of columns are evenly distributed along the cantilever beam. Soil-structure interaction is considered as axial and rotational springs, whose potential energy are formulated and incorporated into overall potential energy of the structure. Subsequently, natural frequency equations are derived on the basis of energy conservation principle. The effect of axial forces on natural frequency is also considered in the proposed formulas. Using the method presented in this study, natural frequencies are computed using a simplified method with no complex numerical modeling. The proposed formulas are verified via experimental and numerical methods. Close agreement between the results from these three approaches are observed. Furthermore, the effects of panel zone flexibility, continuity plates and doubler plates on the natural frequencies of buildings are investigated.展开更多
文摘With an objective of better understanding the nature of India\|Eurasia collision process, as manifest in the NW part of the Himalaya, gravity and GPS aided geodetic studies were carried out during the summers of 1994 through 1996. The area covered includes the Ladakh Himalaya, Indus suture zone (ISZ) and entire NW Himalaya between 74°～80° longitude and 30°～37° latitude. Gravity survey was carried out at 1～2km interval along Kiratpur—Leh—Panamik transect. Four different profiles viz., Kargil—Panikhar; Karu—Tangtse; Mahe—Sumdo and Nyoma—Kyon Tso were also taken. GPS was used, in fast\|static mode for 3\|d position determination of the gravity stations. The collected data were reduced to mean sea level using a new technique of terrain correction (Banerjee, 1998). The collected data was further combined with the published gravity data of SOI (Gulatee, 1956, Chug, 1978); ONGC (Raiverman et al., 1994) and Jin et al., 1994 to produce a new BA map for the NW Himalaya at 10mGal interval. Isostatic anomaly map of the region was also prepared using the BA map and ETOPO\|5 global elevation data set. On the IA map, an isostatic high of about 80mGal is evident over the entire course of the higher Himalaya. This elongated pattern of the gravity high aligns itself over the exposed rocks of central crystallines where the average elevation is 4500m. This 80mGal isostatic high may have been caused due to the fact that isostasy does not strictly prevail in the higher Himalaya and these are in a state of under\|compensation. This IA high has been interpreted in terms of upwarping in the Moho beneath the higher Himalaya. The IA analysis has also led to the depth of Moho to be 36～37km under the foothills, 60～65km under the higher Himalaya and 70～75km under the ISZ and beyond. Doubling of the crustal thickness is evident from the IA analysis and they are in general, in agreement with the DSS results of the Kashmir Himalaya.
文摘New approximate formulas are proposed to determine the natural frequencies of structures considering the effects of panel zone flexibility and soil-structure interaction. Several structures with various earthquake resisting systems are idealized as prismatic cantilever flexural-shear beams. Floor masses are considered as lumped masses at each story level and masses of columns are evenly distributed along the cantilever beam. Soil-structure interaction is considered as axial and rotational springs, whose potential energy are formulated and incorporated into overall potential energy of the structure. Subsequently, natural frequency equations are derived on the basis of energy conservation principle. The effect of axial forces on natural frequency is also considered in the proposed formulas. Using the method presented in this study, natural frequencies are computed using a simplified method with no complex numerical modeling. The proposed formulas are verified via experimental and numerical methods. Close agreement between the results from these three approaches are observed. Furthermore, the effects of panel zone flexibility, continuity plates and doubler plates on the natural frequencies of buildings are investigated.
