Enhancing resilience of highway bridges through seismic retrofit          下载免费PDF全文

Ashok Venkittaraman  Swagata Banerjee 《地震工程与结构动力学》2014,43(8):1173-1191

The present study evaluates seismic resilience of highway bridges that are important components of highway transportation systems. To mitigate losses incurred from bridge damage during seismic events, bridge retrofit strategies are selected such that the retrofit not only enhances bridge seismic performance but also improves resilience of the system consisting of these bridges. To obtain results specific to a bridge, a reinforced concrete bridge in the Los Angeles region is analyzed. This bridge was severely damaged during the Northridge earthquake because of shear failure of one bridge pier. Seismic vulnerability model of the bridge is developed through finite element analysis under a suite of time histories that represent regional seismic hazard. Obtained bridge vulnerability model is combined with appropriate loss and recovery models to calculate seismic resilience of the bridge. Impact of retrofit on seismic resilience is observed by applying suitable retrofit strategy to the bridge assuming its undamaged condition prior to the Northridge event. Difference in resilience observed before and after bridge retrofit signified the effectiveness of seismic retrofit. The applied retrofit technique is also found to be cost‐effective through a cost‐benefit analysis. First order second moment reliability analysis is performed, and a tornado diagram is developed to identify major uncertain input parameters to which seismic resilience is most sensitive. Statistical analysis of resilience obtained through random sampling of major uncertain input parameters revealed that the uncertain nature of seismic resilience can be characterized with a normal distribution, the standard deviation of which represents the uncertainty in seismic resilience. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Grain size analysis and depositional pattern of upper Gondwana sediments (Early Cretaceous) of Salbardi area,districts Amravati,Maharashtra and Betul,Madhya Pradesh     

Ashok K. Srivastava  Rupesh S. Mankar 《Journal of the Geological Society of India》2009,73(3):393-406

A detailed grain-size analysis of twenty-two sandstone samples from the uppermost Gondwana succession of Salbardi area has been carried out to interpret the depositional pattern. The sandstones are mainly medium to coarse grained, moderately sorted, near-symmetrical to fine-skewed and mesokurtic in nature. Inter-relationship of various parameters shows bimodal nature of sediments having dominance of medium sand. Based on the granulometric analysis, a fluvial environment of deposition is interpreted for the succession.  相似文献   

Framboidal — colloform — recrystallised pyrite in the granitoids of Wahkyn area,West Khasi hills,Meghalaya     

N. Ranganath  Ashok Kumar Padhi  Ajoy Kumar Padhi  Ashwini Kumar Rai 《Journal of the Geological Society of India》2009,74(5):591-596

Petrographic studies of Proterozoic pyriteferous granitoids forming basement for upper cretaceous Mahadek sediments from Wahkyn area reveal interesting textural peculiarities of Pyrite. These pyrites also reveal interesting structural peculiarities. The three textural pyrite varieties found in the granitoids are: framboidal, colloform and recrystallised which appear both as composite aggregate as well as independent units. Various textures and variation in reflectivity, microhardness and elemental distribution of the pyrites are described. Average Co/Ni ratio along with the textural manifestation of these pyrites attests their sedimentary origin.  相似文献   

Mathematical analysis of a chaotic model in relevance to monsoon ISO     

Sandipan Mukherjee  Ravi Prakash Shukla  Ashok Kumar Mittal  Avinash Chandra Pandey 《Meteorology and Atmospheric Physics》2011,114(3-4):83-93

Mathematical analysis of a predominantly bimodal chaotic attractor, Lu system, was carried out to investigate a possible application of the model as a prototype of monsoon intra-seasonal oscillation (ISO). Bifurcation structures of the system are explored as the system parameter c and the forcing parameter F are varied. Stability criteria of equilibrium points of the forced Lu system are also explored in detail. A sensitivity study is carried out, by changing forcing parameter F, to explore relationships between some of the derived variables of the model and, based on such relationships, an empirical rule is used for extended range prediction. Analogous variables are also derived from the ISO data and prediction results are compared. Application of the prediction rule of regime transition to the observed ISO and chaotic model data is purely based on the bimodal characteristics of ISO and neglects some of the intricate mechanisms therein. We have found that a forced Lu system can be a good prototype in the prediction of peak anomaly of the monsoon ISO when growth rates around a threshold value are taken as predictors.  相似文献   

Simulation of CO<Subscript>2</Subscript> hydrate formation in cold aquifers: nonequilibrium approach     

Khaled Jemai  Mohammad Taghi Vafaei  Bjørn Kvamme  Ashok Chejara 《Arabian Journal of Geosciences》2017,10(5):113

In this paper, we focus on the geological storage of CO₂ in reservoirs with zones that are cold enough to facilitate CO₂ hydrate formation at local pressures. A 2D hydro-chemical mechanical model which has five layers (three layers with aquifers and two layers with cap rock in which we introduced two fractures) is created. We apply a reactive transport reservoir simulator, RetrasoCodeBright (RCB), in which hydrate is treated as a pseudo mineral. Following the recent modifications to account for hydrate dynamics in the code through a kinetic approach (Kvamme et al., Proceedings of the 7th International Conference on Gas Hydrates (ICGH 2011), 2011b), we have further improved the simulator to implement the nonequilibrium thermodynamic calculations. In the present study, we spot the light on the hydrate formation effects on porosity in different regions, as well as on the flow pattern. These simulations are based on classical relationships between porosity and permeability, but the outline of ongoing modifications is presented as well. A critical question in such systems is whether hydrate formation can contribute to stabilizing the storage, given that hydrates are pore filling and cannot be stable toward mineral surfaces. The implications of hydrate formation on the geo-mechanical properties of the model reservoir are other aspects addressed in this study.  相似文献   

Numerical modelling-based pillar strength estimation for an increased height of extraction     

Ashok Kumar  Rakesh Kumar  Arun K. Singh  Sahendra Ram  Pradeep K. Singh  Rajendra Singh 《Arabian Journal of Geosciences》2017,10(18):411

Underground extraction of total thickness of a thick coal seam in single lift by bord and pillar method increases pillar height during retreat. Field studies found that the increase in pillar height affects the depillaring operation adversely, especially, during caving of the strong/massive roof strata. Dilution in strength due to the increased pillar height caused catastrophic failure of barrier pillars and goaf overriding. This warrants a systematic study of pillar strength variation for the different heights of pillar. A review of different pillar strength estimation approaches for an analysis of the dilution in strength of the heightened pillar suggested that numerical modelling provides a better option for such a systematic study. Accordingly, investigations are conducted on simulated models in laboratory adopting a recognised numerical modelling procedure. The observed nature of variations in pillar strengths with the increase in its height in the numerical models and empirical formula is found to be matched. But a mismatch is found between the strength values of the two approaches with an increase in height of the pillar. Considering validity of the empirical formulation in Indian coalfields, a relationship is developed to incorporate a correction in the strength values of the numerical models. The suggested correction on the basis of this simple study of the pillar strength variation would be helpful for the use of the established simulation tool during the depillaring of a thick coal seam.  相似文献   

Bloom forming species of phytoplankton in two coastal waters in the Southeast coast of India     

K. Thillai Rajasekar  M. Rajkumar  Jun Sun  V. Ashok Prabu  P. Perumal 《中国海洋大学学报(英文版)》2010,9(3):265-272

The results of an investigation carried out during June 2005 to May 2007 on bloom-forming phytoplankton species composition and abundance in the Parangipettai and Coleroon coastal waters(Southeast coast of India) are reported.Air and surface water temperatures(℃) varied from 25.1 to 30.1 and 24.5 to 28.5,respectively,in the former waters and from 25.5 to 31.2 and 25.0 to 29.3 in the latter waters.The respective salinities varied from 6.0 to 28.5 and 5.0 to 33.1 and the respective pH ranged between 7.0 and 8.3 and 7.2 and 8.3.Correspondingly,the dissolved oxygen content varied from 3.1 to 7.5 and 3.1 to 7.9 mgL-1 while the light extinction coefficient(LEC) values ranged between 3.1 and 10.1 and 1.8 and 11.0.The content ranges of inorganic nutrients,i.e.,nitrate,nitrite,phosphate and silicate(μmolL-1),in the Parangipettai and Coleroon coastal waters were:6.5-27.0;1.0-8.9;0.1-3.0 and 15.0-140 and 10.1-23.4;1.2-8.9;0.2-3.1 and 55-125 respectively.The chlorophyll a contents in both waters ranged from 2.0-7.5 μgL-1.Presently,124 phytoplankton species representing different classes were recorded in the Coleroon coast,viz,Bacillariophyceae(77);Dinophyceae(19);Cyanophyceae(15);Chlorophyceae(10) and Chrysophyceae(3),whereas 117 phytoplankton species were recorded in the Parangipettai coast,viz,Bacillariophyceae(66);Dinophyceae(22);Cyanophyceae(19);Chlorophyceae(7) and Chrysophyceae(3).The phytoplankton cell abundance in the Parangipettai and Coleroon coastal waters varied from 290 to 111662 and 140 to 132 757 cells L-1,respectively,with peak diversity(3.38 and 3.52 bits ind-1.) recorded in summer.The maximum abundance occurred in summer coinciding with the stable hydrographical conditions.The seasonal distribution and abundance of phytoplankton are discussed in relation to hydrographical parameters.Totally 31 and 24 species of phytoplankton were found to be bloom-forming in the Parangipettai and Coleroon coastal waters,respectively.Presently Trichodesmium bloom was also observed,which appeared at the 10 fathom level of the coastal water and quickly spread to the marine zone of the Vellar estuary and near the mouth region of the mangrove waters.The Parangipettai and Coleroon coastal waters are subject to long term fluctuations in physico-chemical conditions depending upon the seasonal tidal range and freshwater influx,resulting in a continuous exchange of organic,inorganic,plant and animal matters.  相似文献   

Assessment of Fractionated Aerosols at a Semiarid Region over the Indo‐Gangetic Basin     

Rohini Singh  Pratima Gupta  Ashok Jangid  Anshumala Sharma  Ranjit Kumar 《洁净——土壤、空气、水》2019,47(4)

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Spectral characteristics of high shallow water waves     

V. Sanil Kumar  K. Ashok Kumar 《Ocean Engineering》2008,35(8-9):900-911

The spectral characteristics of shallow water waves with significant wave height more than 2 m based on the data collected along the Indian coast is examined. It was found that the value of Joint North Sea Wave Project (JONSWAP) parameters (α and γ) increases with significant wave height and mean wave period and decreases with spectral peak period. The estimated average value (0.0027 and 1.63) of the JONSWAP parameters, α and γ were less than the generally recommended values of 0.0081 and 3.3, respectively. By carrying out a multi-regression analysis, an empirical equation is arrived relating the JONSWAP parameters with significant wave height, peak wave period and mean wave period. It was found that the Scott spectra underestimate the maximum spectral energy of high waves. The study shows that the measured wave spectra can be represented by JONSWAP spectra with the JONSWAP parameters estimated based on the equation proposed in this paper.  相似文献   

Seepage analysis in a zoned anisotropic medium by the boundary element method     

Ashok K. Chugh  Henry T. Falvey 《国际地质力学数值与分析法杂志》1984,8(4):399-407

A simple and effective extension to the boundary element method for solving Laplace'S equation (?²u = 0) for boundary value problems is presented to solve steady confined and (or) steady unconfined seepage problems in zoned anisotropic mediums. Sample problems indicating the accuracy of results are given.  相似文献