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Capacity Spectrum Method : Energy Based Approach

Sun, 28 Apr 2013 18:30:00 GMT

Title: Capacity Spectrum Method : Energy Based Approach Authors: Patankar, Digvijay Babasaheb Abstract: The capacity spectrum method is a very popular tool in the performance based earthquake resistant design of structures. Though it involves nonlinear static analysis, it can be used to predict the dynamic behaviour of the building under earthquake load. Since the analysis is only static and not dynamic, it is very well suited for the design offices and low end computer terminals as opposed to dynamic analysis which is very resource consuming. There are several methods/variations of methods, to perform the nonlinear static analysis, popularly known as pushover analysis and convert it to capacity spectrum. Displacement based pushover analysis, force based pushover analysis, modal pushover analysis, energy based pushover analysis etc. are some of the variations of pushover analysis. There are a few attempts to consider the change in mode shape but all the methods are silent about the change in frequency due to formation of hinges in the structure. The available codes for building design such as ATC-40 provide some guidelines for getting the capacity spectrum but are not yet developed for proper ductility consideration while converting the pushover curve to capacity spectrum. The present study tries to address the above issues while proposing a new energy based approach to draw capacity spectrum. The chapter 1 introduces the concept of pushover analysis and capacity spectrum concepts. Different approaches to get these curves, their theoretical background, variations and limitations are discussed as a quick review. Chapter 2 is about the review of literature present on these topics. It is found that most of the studies have been carried out in the past on the framed buildings regarding the pushover analysis. In the last few years attempts are also made to consider the effect of torsion. Summarising the various contributions till now, it may be concluded that even in the earlier multimode pushover analysis the effect of different modes on the only static force distribution was considered. Further the spectral acceleration is obtained as a ratio of base shear and α times the weight of the building, where α is the modal mass coefficient. Only the first mode frequency could be utilized to convert the maximum displacement at the top to the spectral acceleration and the corresponding maximum potential energy (P.E.) could be used for equivalence of MDOF and SDOF. Therefore in chapter 3 which follows, the above limitation is removed as explained below. In chapter 3, the new methodology based on energy equivalence consideration is proposed step by step. For the given multistorey building, a displacement profile is applied to the building which is proportional to the effective mode shape. The effective mode shape can be the first mode shape or a combination of first few mode shapes. In the present study, two cases are considered. In the first case, the effective mode shape is considered to be the first mode shape itself whereas in the second case the effective mode shape is considered to be a linear combination of first three modes weighted by corresponding participation factors. After this, a nonlinear static analysis is performed on the structure considering the above displacement profile. Due to the above provided displacement profile, there will be yielding in the structure at a few locations. The yielded structure is again analysed for eigenvalues and mode shapes and the first three mode shapes are extracted along with their participation factors. Again the deflected structure is subjected to the deflection proportional to the effective mode shape and the analysis is continued until the collapse. The chapter also describes the details of the model used for simulation. Two kinds of simulation are performed on the model. One is considering only single mode of vibration whereas the other is considering the multiple modes (3 in this case) of vibration of the structure. Chapter 4 discusses the results of the simulations performed on the model. Single mode and multimode cases are treated and discussed separately. The proposed method is in its nascent stage and hence a lot of modification and validation work is needed to consider the method acceptable. The chapter 5 concludes the overall outcome of the present study and provides scope for the further study.

Analysis Of Groundwater Dynamics In Semi-Arid Regions : Effect Of Rainfall Variability And Pumping

Wed, 06 Feb 2013 18:30:00 GMT

Title: Analysis Of Groundwater Dynamics In Semi-Arid Regions : Effect Of Rainfall Variability And Pumping Authors: Javeed, Yusuf

Studies On Some Aspects Of Liquidity Of Stocks : Limit Order Executions In The Indian Stock Market

Mon, 25 Jun 2012 18:30:00 GMT

Title: Studies On Some Aspects Of Liquidity Of Stocks : Limit Order Executions In The Indian Stock Market Authors: Chatterjee, Devlina Abstract: We study some aspects of liquidity of stocks traded through the National Stock Exchange (NSE) of India. Initially we examine the multi-dimensional nature of liquidity by conducting day-wise factor analysis of eleven liquidity proxies across a cross-section of stocks, using data from two periods reflecting different market conditions. Five factors emerge consistently, interpretable as depth, spread, volume, price elasticity and relative activity. Subsequently, we study execution of limit orders in the NSE from three angles. First we consider order execution probability, using 106 stock-specific logistic models. Important predictors of order execution probability are price premium followed by volatility, relative activity, bid ask spread and order imbalance. Some differences are noted when comparing companies of different sizes and between buy and sell orders. Second, we study order execution times using survival analysis. Several diagnostic tests indicate that parametric Accelerated Failure Time models using the log-logistic distribution for the survival time S(t) are suitable for current data. 100 stock-specific models are built; results are consistent with the logistic models. Additionally depth is also found to be important. Finally we build 4 combined models across stocks for both execution probabilities as well as times. These models perform well on out of sample data, suggesting their predictive utility.

Characterization And Lime Stabilization Studies On Artificially Lead Contaminated Soils

Thu, 07 Jul 2011 18:30:00 GMT

Title: Characterization And Lime Stabilization Studies On Artificially Lead Contaminated Soils Authors: Gaurave, Kumar Abstract: Hazardous waste substances are solid, semi-solid or non-aqueous liquids that exhibit characteristics of corrosivity, reactivity, ignitability, toxicity and infectious property. Major available options for management of hazardous waste include direct disposal into landfill or chemical treatment/stabilization of wastes prior to landfill disposal. Hazardous wastes are accepted for direct disposal in engineered landfills if they conform to the chemical concentration limit criterion (determined by water leach test followed by estimation of the concentration of the contaminant) and compressive strength (the material should have compressive strength > 50 kPa) criterion. Lead is classified as extremely toxic metal. Elevated levels of lead in water (surface and ground water) primarily arise from industrial discharges, and aerial deposition. During its residence in surface water bodies, the lead may interact detrimentally with aquatic life or be abstracted into public water supplies. According to National drinking water standards, the permissible limit of lead in drinking water is 0.05 mg/l. Deposition of air-borne lead, disposal of sewage sludge on land and disposal of industrial effluents on lands are major sources of lead contamination of soils. When incorporated in soil, lead is of very low mobility. Lead retained in soils can be slowly leached to the groundwater thereby impacting human health if consumed for potable needs. Alternatively lead deposited in soils can be absorbed by vegetation (crops/trees) and can impact human health on their consumption. Given the negative impacts of lead contamination on human health, the strong affinity of soils to retain deposited lead and the possible release for human consumption, this thesis focuses on characterization and chemical stabilization of artificially lead contaminated soils in the context of their disposal in hazardous waste landfills. The main objectives of the thesis are: characterize artificially lead contaminated soils for water leachability of lead and undrained strength characteristics as per CPCB (Central Pollution Control Board) guidelines in the context of disposal criteria in hazardous waste landfills. Artificially lead contaminated soils in compacted and slurry states are used in the thesis. Red soil (from Bangalore District, Karnataka) and river sand are used in the preparation of compacted and slurry specimens. The red soil and red soil-sand specimens are artificially contaminated in the laboratory by employing aqueous lead salt solutions as remolding fluids. Lead concentrations of 160 to 10000 mg/l are used in this study. The results of characterization studies with artificially lead contaminated soils help identify contaminated soil materials that require chemical stabilization prior to disposal into engineered landfills. Based on the results of characterization studies with artificially lead contaminated soils, lime stabilization coupled with steam curing technique is resorted to immobilize lead in the red soil-sand slurry specimens and mobilize adequate undrained strength to meet the criteria for disposal of lead contaminated soils in hazardous landfills. After this first introductory chapter, a detailed review of literature is performed towards highlighting the need to undertake chemical stabilization of artificially lead contaminated soils in Chapter 2. Chapter 3 presents a detailed experimental program of the study. Chapter 4 presents the physico-chemical and mechanical characterization of the artificially lead contaminated soils. The ability of artificially contaminated soils to release (artificially added) lead during water leaching is explained using lead speciation results performed using the Visual MINTEQ program. Experimental results illustrated that contamination of compacted red soil and red soil + sand specimens with significant lead concentrations (21 to 1300 mg/kg) resulted in major fractions of the added lead being retained in the precipitated state. Results of water leach tests revealed that lead concentrations released in the water leachates are far less than (0.0011 to 0.48 mg/l) limits prescribed by CPCB (2 mg/l) for direct disposal of lead contaminated materials into hazardous waste landfills. Unconfined compressive strengths developed by the lead contaminated red soil and red soil-sand specimens were significantly higher (100-2700 kPa) than the strength requirement (> 50 kPa) for direct disposal of hazardous wastes in engineered landfills. Lead contamination did not affect the unconfined compression strengths of the specimens as matric suction prevalent in the unsaturated compacted soils had an overriding influence on the cementation bond strength created by the lead precipitates. Visual Minteq tool was helpful in predicting the amount of added lead that was converted to insoluble precipitate form. However the amounts of water leachable lead determined experimentally and predicted by Visual Minteq were very different-Visual Minteq predicted much higher amounts of water leachable lead than experimentally determined. Experimental results revealed that the levels of lead released by the red soil-sand slurries in water leach tests were in excess (13 to 36 mg/l) of the permissible lead concentration (2 mg/l) for direct disposal of hazardous waste in landfills. Owing to water contents generally being in excess of their liquid limit water contents (w/wL ratio > 1) the slurry specimens exhibited undrained strengths below 1 kPa. Lime stabilization and steam curing of the contaminated slurry specimens was therefore resorted to control the leachibility of lead and increase undrained strengths to acceptable limits. Chapter 5 deals with lime stabilization of artificially contaminated slurries that do not meet the leachate quality (lead concentration in water < 2 mg/l) or compressive strength (> 50 kPa). Procedures are evolved for lime stabilization of such artificially contaminated soils to meet both the water leachate quality and compressive strength criteria. Lime stabilization together with steam curing of the lead contaminated slurry specimens effectively immobilized the added lead (2500 mg/kg) and imparted adequate compressive strengths to the contaminated red soil-sand slurry specimens. The lime stabilized contaminated specimens released marginal lead concentrations (0.03 to 0.45 mg/l) in the water leach; these values are much lower than permissible limit (2 mg/l) for disposal in hazardous landfills or values exhibited by the unstabilized specimens (13 to 38 mg/l). Lime addition rendered the contaminated specimens strongly alkaline (pH values ranged between 10.68 and 11.66). Combination of the experimental and Visual Minteq results suggested that precipitation of lead as hydrocerrusite in the alkaline environments (pH 10.68 to 11.95) is not the sole factor for marginal release of lead in water leach tests of the 4, 7 and 10 % lime stabilized contaminated specimens. It is possible that fraction of lead ions are entrapped within the cemented soil matrix. Water leach tests performed at range of pH values (pH 2.5 to 9.6) with 7 % lime stabilized specimens suggested that immobilization of lead as hydrocerrusite or as entrapment in the cemented soil mass in the lime stabilized specimens is practically irreversible even on exposure to extreme pH conditions. The lime stabilized contaminated specimens developed unconfined compressive strengths ranging from 100 kPa (4 % lime stabilized 40 % red soil-60 % sand specimen) to 1000 kPa (10 % lime stabilized 100 % red soil specimen). The significant growth of compressive strength upon lime stabilization is attributed to growth of inter-particle cementation bonds by the CAH (calcium aluminate hydrate) and CSH (calcium silicate hydrate) compounds formed by lime-clay reactions, slight reduction in void ratios and growth of strong inter-particle cementation bonds the during steam curing at 800C. The results of this thesis bring out a procedure to immobilize high concentrations of lead and develop adequate compressive strength of lead contaminated slurry specimens by lime stabilization + steam curing technique. The red soil acted as pozzolana in reactions with lime, while, steam curing accelerated the lime-soil reactions. The procedure can be extended to non-organic slurry wastes that are devoid of pozzolanic material (example, lead contaminated smelting sands). In slurry wastes devoid of pozzolana, materials such as fly ash can be added and the reactions between lime and fly ash would immobilize lead + develop adequate compressive strength. Also, similar to the methodology being adaptable for any non-organic slurries, it can also be extended to other toxic metal bearing wastes, example, zinc, cadmium and nickel.