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31.
In recent earthquakes in developing countries, severe damage was observed on reinforced concrete buildings. This study focuses on exterior beam-column joints with substandard beam rebar anchorage and seismic strengthening by installing wing walls. First, a series of experiments was conducted to investigate the seismic behavior of exterior joints with substandard beam rebar anchorage representing typical Bangladeshi buildings. Two 0.7-scaled exterior joint specimens were tested, and these specimens showed beam rebar anchorage failure and/or joint shear failure. Prior to strengthening of the joint, a series of pullout tests was conducted on postinstalled bonded anchors in low-strength concrete for strengthening design. Then, an experiment was performed to apply the strengthening method by wing walls to one of the exterior joint specimens to improve the integrity, and this method was intended to prevent the failure of beam rebar anchorage. The strengthening method is proposed to extend the development length of beam longitudinal bars by considering the embedment length along the wing walls. The test results verified the effectiveness and applicability of the proposed strengthening method to upgrade exterior RC beam-column joints with deficient beam rebar anchorage. 相似文献
32.
Rockwall slope erosion is defined for the upper Bhagirathi catchment using cosmogenic Beryllium-10 (10Be) concentrations in sediment from medial moraines on Gangotri glacier. Beryllium-10 concentrations range from 1.1 ± 0.2 to 2.7 ± 0.3 × 104 at/g SiO2, yielding rockwall slope erosion rates from 2.4 ± 0.4 to 6.9 ± 1.9 mm/a. Slope erosion rates are likely to have varied over space and time and responded to shifts in climate, geomorphic and/or tectonic regime throughout the late Quaternary. Geomorphic and sedimentological analyses confirm that the moraines are predominately composed of rockfall and avalanche debris mobilized from steep relief rockwall slopes via periglacial weathering processes. The glacial rockwall slope erosion affects sediment flux and storage of snow and ice at the catchment head on diurnal to millennial timescales, and more broadly influences catchment configuration and relief, glacier dynamics and microclimates. The slope erosion rates exceed the averaged catchment-wide and exhumation rates of Bhagirathi and the Garhwal region on geomorphic timescales (103−105 years), supporting the view that erosion at the headwaters can outpace the wider catchment. The 10Be concentrations of medial moraine sediment for the upper Bhagirathi catchment and the catchments of Chhota Shigri in Lahul, northern India and Baltoro glacier in Central Karakoram, Pakistan show a tentative relationship between 10Be concentration and precipitation. As such there is more rapid glacial rockwall slope erosion in the monsoon-influenced Lesser and Greater Himalaya compared to the semi-arid interior of the orogen. Rockwall slope erosion in the three study areas, and more broadly across the northwest Himalaya is likely governed by individual catchment dynamics that vary across space and time. © 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons, Ltd. 相似文献
33.
R. K. Ray T. H. Syed Dipankar Saha B. C. Sarkar A. K. Patre 《Hydrogeology Journal》2017,25(8):2513-2525
Extracted groundwater, 90% of which is used for irrigated agriculture, is central to the socio-economic development of India. A lack of regulation or implementation of regulations, alongside unrecorded extraction, often leads to over exploitation of large-scale common-pool resources like groundwater. Inevitably, management of groundwater extraction (draft) for irrigation is critical for sustainability of aquifers and the society at large. However, existing assessments of groundwater draft, which are mostly available at large spatial scales, are inadequate for managing groundwater resources that are primarily exploited by stakeholders at much finer scales. This study presents an estimate, projection and analysis of fine-scale groundwater draft in the Seonath-Kharun interfluve of central India. Using field surveys of instantaneous discharge from irrigation wells and boreholes, annual groundwater draft for irrigation in this area is estimated to be 212 × 106 m3, most of which (89%) is withdrawn during non-monsoon season. However, the density of wells/boreholes, and consequent extraction of groundwater, is controlled by the existing hydrogeological conditions. Based on trends in the number of abstraction structures (1982–2011), groundwater draft for the year 2020 is projected to be approximately 307 × 106 m3; hence, groundwater draft for irrigation in the study area is predicted to increase by ~44% within a span of 8 years. Central to the work presented here is the approach for estimation and prediction of groundwater draft at finer scales, which can be extended to critical groundwater zones of the country. 相似文献
34.
Traditionally seismic design of structures supported on piled raft foundation is performed by considering fixed base conditions, while the pile head is also considered to be fixed for the design of the pile foundation. Major drawback of this assumption is that it cannot capture soil-foundation-structure interaction due to flexibility of soil or the inertial interaction involving heavy foundation masses. Previous studies on this subject addressed mainly the intricacy in modelling of dynamic soil structure interaction(DSSI) but not the implication of such interaction on the distribution of forces at various elements of the pile foundation and supported structure. A recent numerical study by the authors showed significant change in response at different elements of the piled raft supported structure when DSSI effects are considered. The present study is a limited attempt in this direction, and it examines such observations through shake table tests. The effect of DSSI is examined by comparing dynamic responses from fixed base scaled down model structures and the overall systems. This study indicates the possibility of significant underestimation in design forces for both the column and pile if designed under fixed base assumption. Such underestimation in the design forces may have serious implication in the design of a foundation or structural element. 相似文献
35.
Evaluation of Composts from Agricultural Wastes with Fish Pond Sediment as Bulking Agent to Improve Compost Quality 总被引:1,自引:0,他引:1
Tanmoy Karak Pradip Bhattacharyya Ranjit Kumar Paul Tapati Das Subhrajit K. Saha 《洁净——土壤、空气、水》2013,41(7):711-723
Composts with five different ratios of agricultural wastes, viz. rice straw (RS), wheat straw (WS), potato plant (PP), and mustard stover (MS) were prepared with or without fish pond bottom sediment to investigate the compost maturity and their suitability for field application. The composting process was monitored through the changes in physico‐chemical parameters and germination index (GI) at every 7 days interval of the composting process. All the composts were dark brown and smelled like forest soil within 56 days of composting, which reflected its matured status. On the basis of the physico‐chemical parameters (bulk density: 0.84 g/cm3; pH 7.05; electrical conductivity: 3.52 mS/cm; cation exchange capacity:82.4 cmol/kg; total carbon:321.4 g/kg; total nitrogen: 16.9 g/kg; As: 6.8 mg/kg; Cd: 2.96 mg/kg; Cr: 29.6 mg/kg, Cu: 243.6 mg/kg; Hg: 0.019 mg/kg; Ni: 24.3 mg/kg; Pb: 62.1 mg/kg and Zn: 812 mg/kg) and GI (89–96%), it could be concluded that RS/WS/PP/MS, 1:1:2:1 v/v/v/v with fish pond sediment produced better compost in accordance with the Indian compost standard. Application of a combined randomized block design analysis revealed that there is a significant difference in the responses of the five composts, in relation to the time of composting. Hierarchical clustering algorithm was applied with a view to form homogeneous groups of five different composts on the basis of different physico‐chemical parameters. Therefore, the ratio of waste incorporation is an important decision for composting and addition of pond sediment can improve the quality of compost. 相似文献
36.
Sonali Saha Keith Bradley Michael S. Ross Phillip Hughes Thomas Wilmers Pablo L. Ruiz Chris Bergh 《Climatic change》2011,107(1-2):169-184
We investigate the effects of Hurricane Wilma??s storm surge (23?C24 October 2005) on the dominant tree Pinus elliottii var densa (South Florida slash pine) and rare plant species in subtropical pine rocklands of the Lower Florida Keys. We examine the role of elevation on species abundance in 1995 (Hurricane Betsy in 1965), 2005 (Hurricane Georges in 1998), and 2008 (Hurricane Wilma in 2005) to investigate if hurricanes influence abundance by eliminating plants at lower elevation on Big Pine Key, the largest island in the Lower Florida Keys. We compare densities before and after Hurricane Wilma over the 2005?C2008 sampling period and examine the role of elevation on changes in pine and rare species densities three years after Hurricane Wilma. We use elevation to assess the impact of hurricanes because elevation determined whether a location was influenced by storm surge (maximum surge of 2 m) in the Lower Florida Keys, where pine rocklands occur at a maximum elevation of 3 m. In 1995 (30 years after a major storm), elevation did not explain the abundance of South Florida slash pine or Chamaecrista lineata, but explained significant variation in abundance of Chamaesyce deltoidea. The latter two species are rare herbaceous plants restricted to pine rocklands. In 2008, 3 years after Hurricane Wilma, the positive relationship between elevation and abundance was strongest for South Florida slash pine, C. deltoidea, and C. lineata. Effects of Hurricane Wilma were not significant for rare species with wider distribution, occurring in plant communities adjacent to pine rocklands and in disturbed rocklands. Our results suggest that hurricanes drive population dynamics of South Florida slash pine and rare species that occur exclusively in pine rocklands at higher elevations. Rare species restricted to pine rocklands showed dramatic declines after Hurricane Wilma and were eliminated at elevations <0.5 m. Widely distributed rare species did not show significant changes in density after Hurricane Wilma. Abundance increased with elevation for South Florida slash pine and C. lineata after the hurricane. In an environment influenced by sea level rise, concrete plans to conserve pine ecosystems are warranted. Results from this study will help define conservation strategies by strengthening predictive understanding of plant responses to disturbance in the backdrop of sea level rise. 相似文献
37.
The paper presents the nature of the variation of refractive index of atmospheric medium with time and altitude before, during and after the onset of thunderstorms over Gangetic West Bengal during the pre-monsoon period. A critical analysis shows that sharp depletion of the refractive index takes place before the onset of Nor??westers and possible explanations are also offered for the said occurrence. 相似文献
38.
Organic micropollutants in marine plastics debris from the open ocean and remote and urban beaches 总被引:2,自引:0,他引:2
Hirai H Takada H Ogata Y Yamashita R Mizukawa K Saha M Kwan C Moore C Gray H Laursen D Zettler ER Farrington JW Reddy CM Peacock EE Ward MW 《Marine pollution bulletin》2011,62(8):1683-1692
To understand the spatial variation in concentrations and compositions of organic micropollutants in marine plastic debris and their sources, we analyzed plastic fragments (∼10 mm) from the open ocean and from remote and urban beaches. Polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), dichloro-diphenyl-trichloroethane and its metabolites (DDTs), polybrominated diphenyl ethers (PBDEs), alkylphenols and bisphenol A were detected in the fragments at concentrations from 1 to 10,000 ng/g. Concentrations showed large piece-to-piece variability. Hydrophobic organic compounds such as PCBs and PAHs were sorbed from seawater to the plastic fragments. PCBs are most probably derived from legacy pollution. PAHs showed a petrogenic signature, suggesting the sorption of PAHs from oil slicks. Nonylphenol, bisphenol A, and PBDEs came mainly from additives and were detected at high concentrations in some fragments both from remote and urban beaches and the open ocean. 相似文献
39.
L. Saha N. C. Pant J. K. Pati D. Upadhyay J. Berndt A. Bhattacharya M. Satynarayanan 《Contributions to Mineralogy and Petrology》2011,161(4):511-530
In quartz-free Fe, Na-poor and high-Mg, Al schists from the Bundelkhand craton in north central India, corundum porphyroblasts
in finely interleaved phlogopite–chlorite aggregates with rare clinozoisite are mantled by fine-grained (<3 μm) intergrowths
of outer collars (>200 μm wide) of phengitic-muscovite and chlorite (phlogopite + corundum + H2O → phengitic-muscovite + chlorite), and <100 μm wide inner collars of margarite–muscovite (corundum + clinozoisite + phengitic
muscovite → margarite + muscovite + H2O). Wide-beam electron probe microanalyses indicate Mg in the bi-layered corona increases from corundum outwards, with a complementary
decrease in Al and K. Si and Ca increase and then decrease to matrix values. The sharp chemical gradients across the highly
structured bi-layered corona are inferred to suggest that the corona-forming reactions were promoted by local grain-boundary-controlled
thermodynamic instability as opposed to element transport by advective diffusion. The P–T convergence of KMASH reactions and
NCKMASH pseudosection phase relations computed using micro-domain compositions indicate the chlorite–phengitic muscovite outer
collar formed at 18–20 kbar and ca. 630°C. The NCKMASH margarite–muscovite inner collar yielded lower metamorphic P–T conditions
of 11 ± 3 kbar, ca. 630°C. U–Th–Pb chemical dating of metamorphic monazite and LA-ICPMS U–Pb isotope dating of re-equilibrated
zircon yield ca. 2.78 Ga ages, which are interpreted to date corona formation and Neoarchean high-P metamorphism in the Bundelkhand
craton, hitherto unknown in the Indian Precambrian. (220) 相似文献
40.
Ratan K. Majumder M. A. Halim B. B. Saha Reo Ikawa Toshio Nakamura Makoto Kagabu Jun Shimada 《Environmental Earth Sciences》2011,64(5):1343-1352
A total number of 328 groundwater samples are analysed to evaluate the groundwater flow systems in Bengal Delta aquifers,
Bangladesh using environmental isotope (2H, 18O, 13C, 3H, and 14C) techniques. A well-defined Local Meteoric Water Line (LMWL) δ2H = 7.7 δ18O + 10.7 ‰ is constructed applying linear correlation analyses to the monthly weighted rainfall isotopic compositions (δ18O and δ2H). The δ18O and δ2H concentrations of all groundwater samples in the study area are plotted more or less over the LMWL, which provides compelling
evidence that all groundwaters are derived from rainfall and floodwater with a minor localized evaporation effects for the
shallow groundwaters. Tritium concentration is observed in 40 samples out of 41 with values varying between 0.3 and 5.0 TU,
which represents an evidence of young water recharge to the shallow and intermediate aquifers. A decreasing trend of 14C activity is associated with the heavier δ13C values, which indicates the presence of geochemical reactions affecting the 14C concentration along the groundwater flow system. Both vertical and lateral decrease of 14C activity toward down gradient show the presence of regional groundwater flow commencing from the unconfined aquifers, which
discharges along the coastal regions. Finally, shallow, intermediate, and deep groundwater flow dynamics has revealed in the
Bengal Delta aquifers, Bangladesh. 相似文献