Aluminium shear-links for enhanced seismic resistance     

Durgesh C. Rai  Benjamin J. Wallace 《地震工程与结构动力学》1998,27(4):315-342

An aluminium beam shear-link is developed for earthquake-resistant structures. The aluminium beam is designed to yield in shear mode to limit the maximum lateral force which is transmitted to primary structural members and to provide significant energy dissipation potential. Aluminium was chosen because of its low yield strength, which enables the use of thicker webs, reducing the problems of web buckling. Cyclic load tests on medium scale (1:4) models were conducted to study the hysteretic behaviour and energy dissipation potential of shear-links made of two alloys of aluminium (3003-O and 6061-O). The links were also tested at faster rates (cycling frequencies of 5, 10 and 17 Hz) to determine the effect of strain rate. The links exhibited very ductile shear yielding and excellent energy dissipation capacity. Unpinched and full hysteresis loops were observed until 10 per cent shear strain, and a relatively small influence of strain rates was observed on the link's performance. Simple design equations are developed to proportion these shear-links, using data from the cyclic load tests. In chevron-type braced systems, the shear-link is sandwiched between the tops of diagonal braces and a girder from the floor above, resulting in yielding at a lateral force less than that required to buckle the compression brace. A Shear-Link Braced Frame (SLBF) system was designed and its seismic performance was compared to that of an Ordinary Concentric Braced Frame (OCBF) with chevron braces. The SLBF system demonstrated more uniform distribution of storey drifts, reduced base shear, and a larger energy dissipation capacity per unit drift. © 1998 John Wiley & Sons, Ltd.  相似文献   

PSR B1237+25的强脉冲辐射特性的观测与研究          下载免费PDF全文

麦麦提艾力·米吉提  温志刚  王娜  王兆军  袁建平  YUEN Rai  闫文明 《天文学报》2021,62(1):1-16

强脉冲是一种特殊的单脉冲辐射,表现为较强的射电爆发.利用新疆天文台南山25 m射电望远镜研究了PSR B1237+25的强脉冲辐射特性.发现探测到的793个强脉冲出现在积分轮廓的所有辐射成分中,峰值流量密度是平均脉冲的10.2至82.5倍.用对数正态分布对强脉冲的峰值流量密度比、信噪比和脉冲宽度的分布进行了拟合.在15...  相似文献   

Determination of the particle load based on detailed suspended sediment measurements at a hydropower plant     

Anant Kumar Rai  Arun Kumar 《国际泥沙研究》2019,34(5):409-421

Suspended sediment particles contained in inflows of water systems of hydropower plants (HPPs) cause hydro-abrasive erosion of the hydraulic turbines and structures leading to significant maintenance costs, efficiency reductions, and downtime. Relevant parameters such as suspended sediment concentration (SSC), particle size distribution (PSD), shape, and mineralogical composition were measured with an online multi-frequency acoustic instrument and based on manually taken samples from the end of the sand trap of the Toss HPP in the Himalayan region, India. In the laboratory, the samples were analyzed using the gravimetric method, laser diffraction, turbidity, dynamic digital image processing, scanning electron microscope, petrography analysis, energy-dispersive X-ray spectroscopy, and X-ray diffraction. The online instrument and the samples provided measurement results at a single point. To investigate vertical gradients in concentration and particle sizes, additional samples were collected 9 times at 7 relative water depths. The SSC, most particle sizes, and particle shape were found to be evenly distributed over depth except d90, i.e. the diameter which is not exceeded by 90% of the particle mass. d90 measured at 76% of the water depth was in the range of fine sand and was multiplied by 1.05 to obtain an average value representative for the entire depth. Improved methodologies to quantify both particle shape and size in an analytical model for hydro-abrasive erosion are proposed. Also, the PSD measuring performance of laser diffraction and dynamic imaging was studied and similar values of the median particle sizes were obtained from both instruments. Further, multi-frequency acoustic, turbidity and laser diffraction techniques were found suitable for SSC measurement at the test case HPP.  相似文献   

The Detection and Investigations of Strong Pulses from PSR B1237+25     

MIJIT Mamatali  WEN Zhi-gang  WANG Na  WANG Zhao-jun  YUAN Jian-ping  YUEN Rai  YAN Wen-ming 《Chinese Astronomy and Astrophysics》2021,45(2):172-189

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Combined interplay of the Atlantic multidecadal oscillation and the interdecadal Pacific oscillation on rainfall and its extremes over Indian subcontinent     

Manish K. Joshi  Archana Rai 《Climate Dynamics》2015,44(11-12):3339-3359

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Nonlinear Dynamics of Kinetic Alfvén and Whistler Waves in the Solar Wind     

Rajesh Kumar Rai  Swati Sharma  R. P. Sharma 《Solar physics》2017,292(3):42

In this article we investigate the nonlinear dynamics of 3D kinetic Alfvén waves (KAWs) and quasi-transverse weak whistler waves in a magnetized plasma. We have studied the problem numerically to examine the transient evolution of localized structures of 3D KAWs and whistler waves. The nonlinearity arises as a result of ponderomotive effects associated with 3D KAWs; consequently, the background density modifies. The weak whistler waves propagating in this modified density are localized and amplified. To improve our insight into the basic physics behind the formation of these localized structures, we have also solved the system semi-analytically. The power spectra show a Kolmogorov scaling (with a power of \(-5/3\)) in the inertial range that lies above the ion gyroradius. Below this scale, dispersive effects start to appear, and the power spectrum follows a steeper scaling (?2 to ?4). Our results show the important role that KAWs and whistler waves play in the energy cascading from larger to smaller scales. The results are consistent with the solar wind observations by the Cluster spacecraft.  相似文献   

Isotopic and geochemical studies of groundwater from the Ramganga basin and the middle Ganga Plains: implication for pollution and metal contamination     

S. K. Tiwari  S. K. Bartarya  S. K. Rai  Anil K. Gupta  A. K. L. Asthana 《Environmental Earth Sciences》2016,75(16):1170

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Deciphering Geothermal resources in Deccan trap region using electrical resistivity tomography technique   总被引：1，自引：0，他引：1  

Dewashish Kumar  S. Thiagarajan  S. N. Rai 《Journal of the Geological Society of India》2011,78(6):541-548

Exploration of Geothermal resources is important from energy point of view. Western margin of volcanic Deccan traps, also known as Western Ghats, is characterized with the presence of numerous hot springs. The resistivity contrast for the geothermal reservoir rock and the surrounding host rock is significantly high in volcanic terrain which is the case of present study. In such cases the resistivity associated with geothermal reservoirs usually varies from <5 to 15 Ohm-m regardless of how high resistivity is outside the reservoir zone. Direct current (DC) resitivity method is proved to be more suitable method for delineation of groundwater reservoirs. The present work describes the results of electrical resistivity tomography survey carried out at four hot spring sites located at Unhavare (Khed), Tural, Rajwadi and Aravali villages of Chiplun taluk in Ratnagiri district of Maharashtra for delineation of the geothermal reservoirs and associated geological features like faults and fractures responsible for vertical movement of geothermal water with the sole purpose of harnessing geothermal energy. In addition to this, the present study is also aimed to delineate the groundwater reservoirs with normal temperature for exploration purpose to meet the local water supply demand. The interpreted results of the field data suggest the presence of two potential geothermal reservoirs at Unhavare (Khed) and one each at Tural and Aravali. Potential groundwater zones with normal temperature are also delineated for groundwater exploration at Rajwadi and Aravali sites.  相似文献   

Seismic noise array measurements using broadband stations and vertical geophones: preliminary outcomes for the suitability on f-k analysis     

J. J. Galiana-Merino  A. K. Mahajan  C. Lindholm  J. Rosa-Herranz  A. K. Mundepi  Nitesh Rai 《Bulletin of Earthquake Engineering》2011,9(5):1309-1325

In recent years, seismic noise array measurements have emerged as a promising way for estimating Vs profiles and characterizing the corresponding soil structure. Although methods based on analysis of seismic noise are simpler, cheaper and faster than conventional soil penetrating techniques, array deployment requires the use of several stations which are not always available for all the research groups. Broadband stations are expensive, but even short-period sensors can require a significant economical effort as it is necessary to use several. In this paper, the results from broadband stations and vertical geophones using the f-k method have been compared. Circular arrays with both types of instruments were installed north and south of the Himalayan Frontal Thrust (HFT) also known as Mohand Thrust, with different soil characteristics. The comparison carried out in terms of dispersion curves shows an excellent agreement between broadband stations and geophones recordings in the frequency range of applicability of the arrays used. These results indicate the possibility of using seismic refraction equipments for the f-k analysis in the frequency band of geotechnical engineering interest. This has potentially great importance since the same equipment is indicated to be applicable for both seismic noise measurements as well as for active reflection seismic surveys.  相似文献   

Ground Support Strategies at the Turquoise Ridge Joint Venture, Nevada     

L. A. Sandbak  A. R. Rai 《Rock Mechanics and Rock Engineering》2013,46(3):437-454

Weak rock masses of high grade Carlin-trend gold mineralization are encountered in the Turquoise Ridge Joint Venture underground mine. The sediments consist of very weak and altered limestone, mudstone, and carbon-rich clays. The rock mass ratings are described as very poor to poor (Bieniawski in Proceedings of the symposium on exploration for rock engineering, Johannesburg, South Africa, pp. 97–106, 1976). The undercut and fill or boxes stoping mining methods are used because of the low dipping ore body geometry, complex geology, and weak rock mass. Design criteria are chosen to keep openings in weak rock as small as possible to prevent unraveling and to minimize supplementary support. Typical ground support for drifting includes the use of bolts, mesh, spiling, and shotcrete. Quality control of cemented rock fill (CRF) through sampling and aggregate sieve testing is necessary to insure high support strength. Specific support may include shotcrete arches with steel ring sets and CRF “arches” as a replacement of weak rock masses around long-term mine openings. Movement monitoring is utilized in problem areas and is needed to quantify and validate computer modeling.  相似文献