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Many structures such as buildings, power plants, stacks, sea walls, bunkers, and tanks are built with reinforced concrete; and durability is a major concern. Corrosion of reinforcement is the most important process of deterioration. Reinforcement corrosion is prevented by maintaining appropriate quality of concrete mix, casting, and curing and by providing the requisite clear cover to reinforcement according to the postulated exposure. The provisions of several international codes were reviewed from these aspects. Many codes can be interpreted in favor of providing different clear covers on different faces of members in a reinforced concrete structure. The authors' interpretation of the Australian and New Zealand codes revealed that these specifically allow the above. However, this practice might lead to severe durability-related concerns, particularly due to corrosion of reinforcement. Case studies conducted with postulated data from a few international codes revealed that internal corrosion cracks might occur earlier than external cracks in certain cases. Internal cracks can be hidden from view and consequently lead to higher damage to the structure prior to detection. For the simultaneous occurrence of corrosion cracks on the internal and external faces of a member, the internal surface chloride concentration would have to be between 18% and 73.2% of the external, with a median of 38%. These could hardly occur in practice—except for treated air facilities. If construction periods are long, this durability issue would be applicable even for treated air facilities. Higher differences in clear cover between internal and external faces, and higher external chloride exposure – both call for larger reduction of chloride exposure from external to internal. Unless the members are designed for corrosion as specified in some (Japanese) codes, the authors advocate the conservative option of using the same cover for all faces of concrete members to achieve a lower life cycle cost of the facility. Practical Applications: Design codes across the world can be interpreted in favor of different clear covers (to reinforcement) on different faces of concrete members according to exposure conditions. Only the Australian and New Zealand codes specifically mention different clear covers for internal and external faces, by the authors' interpretation. This article examines the durability of concrete members with different clear covers on internal and external faces, with case studies generated from a few international codes. The results indicate that in such cases, corrosion cracks might occur on internal surfaces much earlier than the external surfaces. For cracks to occur simultaneously on both surfaces, the internal surface chloride concentration must be as low as 18% of the external, which is difficult to ensure in practice. Early internal cracks could be hidden from view on account of equipment or false ceiling/panels—thereby causing more damage before detection. They would be difficult to detect, to evaluate, and to carry out structural repairs. Therefore, it could be expensive to maintain and could adversely affect the service life of the structure. This study would sensitize the clients, regulators, and engineers to these concerns. The authors suggest that the conservative approach of the same clear cover may be adopted on all faces, according to the worst exposure on any face, to ensure the durability of the concrete structures. [ABSTRACT FROM AUTHOR]

Across the world, the acceptance criterion for concrete made with non-potable water (SA) is stipulated for mean strength with reference to similar concrete made with potable water (SP). The basis for the strength design of concrete is the characteristic strength. The effect of the acceptance criteria on the characteristic strength of SA and SP was examined using statistical simulations, for the first time. It was found that, compared with a two-sample set, using a three-sample set would improve the characteristic strength of SA. A higher allowable ratio between the means of SA and SP and a lower deviation of individual samples from the mean would improve the characteristic strength of SA. The effect of the coefficient of variation (CoV) of the original population on the characteristic strength of SA varied. On the one hand, a higher CoV reduced the characteristic strength of SP, thereby increasing the probability of SA strength being higher than SP strength. On the other, a higher CoV of SP meant a wider spread of the samples and that could increase the CoV of SA, thereby reducing the characteristic strength of SA. Probabilistic charts were developed for the characteristic strengths of SA and SP for different combinations of the aforementioned variables, with guidance for practical application. [ABSTRACT FROM AUTHOR]

India is dependent on rainfall for agriculture, food security and economic advancements. Spatial and temporal variability of rainfall is well reported, as well as the recent upsurge of extremes due to climate change. In Maharashtra, rainfall intensity varies widely from very high (coasts) to low (west-interior). Extreme value analysis (EVA) of heavy annual rainfall for the various districts of Maharashtra was conducted to ascertain the following for each district: suitable extreme value distribution; extreme (high) annual rainfall; efficacy of gap-filling for missing annual record/s. The suitability of various statistical distributions for representing high annual rainfall values was evaluated using Anderson–Darling test (quantitative), quantile and probability plots (qualitative). The gap-filling exercise resulted in minor variations (<10%) in the estimated extremes, positive as well as negative, for different cases. Therefore, the results of EVA on the actual records are advocated. The suitable distributions for 35 districts are presented in maps and Frechet distribution was adjudged suitable for almost 60% of districts. The estimated extremes for all districts are listed for different return periods for ready reference. These values would be useful for the planning and construction of hydraulic structures, water resources and reservoir management, design and planning of irrigation. Research highlights: Suitable probability distribution functions for modelling the extremes of annual rainfall in each district of Maharashtra have been identified and the parameters have been provided. Extreme values of annual rainfall for each district in Maharashtra for selected return periods have been presented. Evaluation was performed on whether the gaps in the annual rainfall records would affect EVA of the annual rainfall in the districts of Maharashtra. [ABSTRACT FROM AUTHOR]

Sustainable development goal 6: clean water and sanitation—could be a big challenge for water-stressed India. Use of non-potable water for concrete production can contribute largely towards this goal. Scattered experimental studies on concrete mixed with non-potable water having different pH, were collated to prepare a pan-Indian database. Using this data, probability of code compliance of Indian concrete for varying ranges of pH value of mixing water, within the limits permitted by the Indian code (6–8.5), were estimated for the first time in India. A bootstrap-based re-sampling approach was employed for this purpose. The results indicated that fulfilling the 28-day strength requirements would possibly concurrently fulfill similar stipulations for 7-day strength for Indian concrete mixed with non-potable water of varying pH. However, the probabilities of meeting the Indian code requirements were between 54%-66% for pH ranges starting from 6; and between 66%-85% for others (95% confidence). Considering the entire range of pH (6–8.5), this probability was 66% for 28-day and 72% for 7-day (95% confidence). Probabilistic approach for examining the strength/setting time compliance, along with inclusion of 7-day strength as well as durability aspects in future experiments would help to promote use of non-potable sources of water and reduce use of freshwater for mixing concrete in India. [ABSTRACT FROM AUTHOR]

Aggressive cultivation practised across the Indian subcontinent to meet the growing food demands results in the groundwater at many places being severely affected by salinity, and this is a recognised hazard of agricultural belts. Evaluating spatial variations of salinity hazards is important for managing agricultural activity and implementing suitable and timely remedial measures. A precise representation of spatial variations of groundwater salinity using electrical conductivity (EC) can help identify potential sources and evaluate their severity and spatial impact. Simple spatial interpolation schemes, viz., inverse distance weighted (IDW) and trend surface analysis (TSA) are evaluated with over 250 EC measurements in groundwater during two seasons from saline-impacted regions of northwest India. Considering the three performance metrics, namely, correlation coefficient, root mean square error and mean absolute error, IDW scheme was adjudged better than TSA for both seasons. Interpolation by TSA and contour plot using OriginLab® software resulted in unrealistic (negative) values of EC, whereas IDW was free from such limitations. Errors associated with IDW-based interpolated EC values for this site would be 320–415 μS/cm for pre-monsoon and 630–800 μS/cm during post-monsoon seasons. Refined EC map generated using seasonal IDW interpolation scheme would facilitate timely and cost-effective remediation of salinity hazard, impact assessment of point and non-point sources on salinity hazard. Research highlights: Simple algorithms were examined for spatial interpolation of groundwater EC; IDW was adjudged better over TSA. Seasonal influence on interpolation parameters for EC was highlighted. IDW parameters ascertained from systematic search in this study are different from reported default values in commercially available software. Whereas TSA or default interpolation with OriginLab® resulted in negative(unrealistic) EC values, IDW results were consistent. Refined EC map generated using seasonal IDW interpolation scheme would facilitate: timely and cost-effective remediation of salinity hazard; impact assessment of point and non-point sources on salinity hazard. [ABSTRACT FROM AUTHOR]

India experiences rainfall from southwest and northeast monsoon, with large spatial and temporal variability reported in recent years. Rainfall trend could be essential for disaster preparedness or long-term planning of agriculture and economic advancement. Long-term and short-term trends observed in rainfall across different subdivisions of India could be different. The result of trend (or any other) analysis could vary when different tests are employed and hence it is advisable to employ more than one test for any statistical check. Therefore, four tests were employed for detection of trend including Mann-Kendall test, Spearman's Rank Order Correlation test, Wald-Wolfowitz Run test on data, and Wald-Wolfowitz Run test on successive difference of data; and the slopes were estimated by Sen's slope as well as linear regression analysis. For detection of possible change point, the four tests included Pettitt's test, Von Neumann Ratio test, Buishand's Range test, and the graphical test of Cumulative Departures from Mean. Cases of conflicting results in the four tests were addressed with categorical inferences: useful (one or less test rejects null hypothesis); doubtful (two tests reject null hypothesis); suspect (three or more test rejects null hypothesis) – based on approach described in literature. For seven subdivisions in India, trend was statistically significant at 5% level, out of which for five subdivisions, change point was also identified. Decreasing trend was observed for: Nagaland, Manipur, Mizoram, and Tripura; East Uttar Pradesh; East Madhya Pradesh; and Chhattisgarh, whereas increasing trends were identified for Konkan and Goa; Coastal Karnataka; and Telangana. Change point was detected for four other subdivisions as well. The mean was observed to be unstable for nineteen subdivisions, which included all nine subdivisions with identified change points. The short-term trend was found to be at variance with the long term trend in several subdivisions and significant trend was observed for Saurashtra, Kutch and Diu in the last quarter period (1980–2016). Such findings highlight the necessity of short-term trend analysis for indications of possible climate change effects on recent rainfall records. [ABSTRACT FROM AUTHOR]

Generalised dimensionless temporal patterns of rainfall were developed using 17 yr-long hourly rainfall records from Tarapur, on the west coast of India, in conventional approach and without any synthetic tweaking of observed rainstorms. Higher percentile curves (higher intensity rainstorms), as well as lower duration rainstorms, produced steeper initial segments, reflecting site-specific rainstorm characteristics, typical for southwest monsoon rainfall occurring at Tarapur. Patterns derived at Tarapur differed from NRCS Type-III curves for tropical rainfall in US, which has the steepest segment in the middle. Compared to regional studies applicable for Tarapur, site-specific curves were conservative. A proposed risk metric indicated that local infrastructure and hydraulic elements might get underdesigned, if generic rainfall pattern is adopted. The curves thus generated would be inputs for development/augmentation of local infrastructure facilities, accommodating climate change scenarios, especially for important industrial or nuclear installations at and around Tarapur. This is the first study to analyse the departures of site-specific temporal distribution from generic rainfall curves available in literature, for tropical rainfall in the Indian subcontinent. Research highlights: Site-specific temporal patterns of rainfall were generated and compared to generic curves for the first time in India, for Tarapur, a location on west coast of India. When compared to the generic temporal patterns of rainfall applicable for Tarapur, the developed curves were usually conservative. The generic temporal patterns were closer to 95 percentile of site-specific pattern till around first 20% duration of storm, and were closer to the 85 percentile pattern subsequently. A risk metric is proposed for evaluation of the flooding risk of earlier designs based on generic temporal distribution of rainfall from literature or earlier site-specific distributions as well. [ABSTRACT FROM AUTHOR]

Climate change has reportedly resulted in higher magnitude and frequency of extreme weather variables in many parts of India. Such studies pertaining to rainfall were based on long-period records, gridded rainfall data, or climate model projections, which have inherent uncertainties. As long-period records might not be available for many locations, gridded data or climate model analysis could be supplemented with the examination of short-period observations (< 20 years) for climate change effects. Detecting climate change effect from short-period high-resolution data has not yet been reported in the literature. For such exercise, this study proposes a framework based on trend analysis along with a demonstration case at a coastal site in India. Using the proposed analysis, indications of climate change are identified in short-period (January 1997 to December 2013: 17 years) high-resolution (hourly) rainfall data, which are subsequently corroborated with results from long-period (60-year) annual data from the site. This proof-of-concept study opens up an intriguing possibility of detecting climate change indications from short-period data, subject to validation on a larger scale with observations from more weather stations. The results could aid judicious decision-making regarding safety margins required in hydraulic design, to account for climate change effects. The methodology, if corroborated with more studies, might prove useful for detecting climate change effects from other short-period hydro-meteorological data as well. [ABSTRACT FROM AUTHOR]

Increasing trend of number and intensity of the extreme precipitation events in India has been reported in literature. Majority of the Indian weather stations have historical rainfall data recorded at a fixed time (0830 hours) of the day, which could be a limitation for correct estimation of extremes. To overcome this, clock hour correction factor (CHCF) in extreme value analysis (EVA) assumes importance. With hourly rainfall data from a site on western coast of India, CHCF was estimated and compared with those reported in literature. The CHCF estimated in this study was higher than those suggested for India in literature or codes. Further, the effect of the CHCF on EVA was examined for India taking CHCF from literature and Indian standards. Towards this, EVA was performed with fixed window (FW) maxima (with CHCF) and sliding window (SW) maxima obtained from the hourly rainfall records of the site. The extreme rainfall from EVA with FW monthly maxima (68 entries) along with CHCF was conservative, compared to those with SW monthly maxima. Annual FW data (17 entries) resulted in unacceptable extreme values (with or without CHCF). This could be due to the insufficient data length and different distribution shape for annual FW data. Treating each monsoon month as a block in Block Maxima approach or adopting suitable threshold in Peak-Over-Threshold approach could help to increase data length for EVA from shorter record length of rainfall data. [ABSTRACT FROM AUTHOR]

Chloride ion is an important indicator of water quality. Field measurement of chloride is difficult whereas laboratory measurement is both time-consuming and chemical intensive. The conservative nature of chloride and good correlation with electrical conductivity (EC) justifies its use as proxy for chloride estimations. Comparison of the best regression models (RMs) and data-driven decision tree (DT) model enables appreciation of relative merits of the two approaches for this purpose. Quantitative improvements over the models from literature are, increase in correlation (RM: 0.70 to 0.77; DT: 0.70 to 0.78) and decrease in relative errors (RM: MARE: 0.88 to 0.65 and RMSRE: 1.91 to 0.92; DT: MARE: 0.88 to 0.40; RMSRE: 1.91 to 0.54); thereby, DT has emerged as the better modeling approach for this case. Considering the influence of seasonality (pre-or post-monsoon) and degree of saturation of soil (water logged or water depleted) enabled the reduction of the correlation range (0.24–0.87) of the basic variables to a smaller range (0.44–0.89) for estimates of Cl−, along with relative error ranging from 0.35 to 0.57, the improvement being more pronounced for lower value of variable correlations. The overall comparison using the evaluation datasets between RM from literature and RM/DT models from this study exemplified that for the study area, the case-specific models developed using the data-driven tool: DT resulted in the most accurate estimation of chloride in groundwater from the chosen proxy: EC. [ABSTRACT FROM AUTHOR]

Slab-on-grade construction is popular for heavily loaded ground floor slabs. For design, graphical or tabular methods are recommended by US standards. Scattered design formulations for various loadings, namely, wheel load, distributed load, line load, and concentrated load, are compiled in this article from the literature. The effects of the three pertinent factors, namely, modulus of subgrade reaction, allowable tensile stress in concrete, and load contact area, over the design thickness are examined with a parametric study. The design depth of a slab is more sensitive to the lower values of the modulus of subgrade reaction. The allowable stress in concrete affects the design thickness more for the lower modulus of subgrade reaction, and, therefore, the concrete strength and factor of safety should be carefully chosen in such cases. The contact area of loads (wheel/concentrated) generally do not affect the design depth much, except for a contact area radius that is higher than 75 mm in one formula for concentrated loads. Now, to control cracking due to thermal or shrinkage effects, nominal reinforcement is provided in unreinforced grade slabs according to national (Indian) requirements. Taking advantage of this reinforcement, thickness reduction can facilitate economical construction. A nomogram is available in the literature for that purpose. To avoid human error in the application of the nomogram, a generalized expression was developed in this study. Using this equation, the percentage reduction in the unreinforced thickness of the slab on grade on account of the given percentage reinforcement can be directly estimated, regardless of the system of units followed. Alternatively, the reinforcement provided in existing grade slabs may be used to enhance their load-carrying capacity, and tables and charts showing the (notional) increase in the depth of slabs on grade are provided as well. [ABSTRACT FROM AUTHOR]

Despite some researches indicating the possibility of correlation being induced by the common variable effect, correlation plots of ionic ratio (Na+/Cl−) versus ionic concentration (Cl−) still remain popular for interpreting the causes of groundwater salinization. There were doubts about relevance of spurious correlation in groundwater and its detection using the randomization process, owing to the fact that groundwater is charge-balanced and randomization would result in abnormal ionic ratios. In this context, the relevance of spurious correlation and its detection using randomization of common variable was established in this study, which was missing from the literature. The study used qualitative and quantitative tools for detecting the possibility of induced correlation and demonstrated the efficiency of the proposed method using published datasets from a variety of geochemical processes of groundwater salinization. In five out of the eight cases examined, the correlations observed in the plots appeared to be induced by the common variable effect and, as such, were deemed unreliable as positive indicators of the stated salinization processes. Even when the correlations appear not to be induced, it is recommended to always support the inferences with other independent evidence(s). [ABSTRACT FROM AUTHOR]

The rainfall data is available for India majorly as 24-hour records, taken between 08:30 hours on consecutive days. Indian Meteorological Department (IMD) is establishing continuous recording rain gauge network, but sufficient sub-daily data would become available only after a few decades. Consequently, practicing engineers resort to generic time distribution curves to obtain sub-daily rainfall. Time distribution curves for rainfall available for India includes Central Water Commission-Indian Meteorological Department-Ministry of Surface Transport (CWC-IMD-MoST) curves for various zones and IMD-CWC curves for few river basins, respectively. Time distribution curves of rainfall are also available in international literature, namely, Standard Project Storm (SPS) and Technical Report No. 55 (TR55), both developed for USA. In this article, all these curves are evaluated for accuracy at a coastal site near Mumbai, India, which predominantly receives south-west monsoon rainfall. From the study, it is concluded that whereas SPS (index rainfall: 8 inches) and TR55 curves would, in general, provide safe (though uneconomic) design, adoption of SPS (index rainfall: 20 inches) curve, CWC-IMD-MoST curve (subzone 5a & 5b) or IMD-CWC curve for Catchment No. 102 for west flowing rivers would result in unsafe hydraulic design for this site. The deviations could be attributed to different rainfall characteristics at foreign locations or due to temporal, areal and ensemble averaging for the river basins in India. Rather than adoption of generic curves from literature, site specific time distribution curve for rainfall would be preferable for safe and economic design of important hydraulic structures. [ABSTRACT FROM AUTHOR]

The article presents the discussion on indicating the limitations in application of maximum likelihood estimation (MLE). Topics include providing a short literature review on development of Anderson-Darling test as a model diagnostic tool for continuous probability distribution functions; and evaluation of the parameters of extreme value distributions such as graphical method, method of moments, order statistics approach, and maximum likelihood estimation (MLE).