Department of Civil & Infrastructure Engineering

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The present work demonstrates an efficient method for reliability analysis using sequential development of the stochastic response surface. Here, orthogonal Hermite polynomials are used whose unknown coefficients are evaluated using moving least square technique. To do so, collocation points in the conventional stochastic response surface method (SRSM) are replaced by the sparse grid scheme so as to reduce the number of function evaluations. Moreover, the domain is populated sequentially by the sparse grid based on the outcome of the optimization to find out the most probable failure point. Hence, the support points are generated based on a coupled effect of the optimization for failure region and the sub-grids hierarchy. Continuous and differentiable penalty function is imposed to determine multiple failure points, if any, by repeating the optimization. Once the response surface is developed, reliability analysis is carried out using importance sampling. Five different benchmark examples are presented in this study to validate the performance of the proposed modeling. As the accuracy of the method is established, two reliability-based design examples involving nonlinear finite element (FE) analysis of plates are demonstrated. Numerical study shows the efficiency of the proposed sequential SRSM in terms of accuracy and number of time-exhaustive evaluation of the original performance function, as compared to other methods available in the literature. Based on these results, it may be concluded that the proposed method works satisfactorily for a large class of reliability-based design problems. © 2019 World Scientific Publishing Company.

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International Journal of Computational Methods

Sequential stochastic response surface method using moving least squares-based sparse grid scheme for efficient reliability analysis

Hydrological processes are continuously evolving over time under the influence of a number of factors including climatic changes. The effect of these factors leads to the nonstationary nature of hydrologic time series. This chapter focuses on the potential of wavelet transform (WT) to deal with the hydrologic time series prediction considering its time-varying nature. This chapter first presents a brief theoretical background of wavelet transform. Next, a few applications of basin-scale drought predictions are presented to demonstrate the potential of wavelet-based models. When applied to two basins of different sizes, the wavelet-based method is found to satisfactorily capture the interrelationship between different types of droughts and their propagation from one type to another. It should also be noted that the methodology presented is general and can be applied to similar problems dealing with hydrologic prediction. © 2019, Springer Nature Switzerland AG.

Hydrology in a Changing World

Predictability of hydrological systems using the wavelet transformation: Application to drought prediction

Coal combustion residue (CCR) has gained considerable acceptance in civil engineering applications, mainly in the cement industry and brick manufacturing. However, despite an increasing application of CCR, a large proportion remains unutilized globally. This research focuses on the feasibility of using fly ash, bottom ash, and their mixtures as a filling material in reinforced soil structures (RSS). The physical, mechanical characterization of the materials, along with the pullout resistance behavior of the interface between the CCR and a uniaxial polyester geogrid was studied. The grain size distribution tests showed the presence of 80% silt particles in fly ash and 7% in bottom ash. All the CCR samples were non-plastic in nature, and direct shear test results revealed that well compacted CCR samples offer similar shear strength as that of natural soils used as backfill in RSS. The leachability tests of CCR were carried out as per EN 12457–4 (2002) for the assessment of environmental risk. The results revealed that the leachable toxic contents in CCR remained quite below than the standard prescribed limits defined by the European Council Decision 2003/33/EC. The interaction coefficient values for a bottom ash-geogrid interface, obtained from the pullout test, match well with the results of natural/conventional fill material. The interaction coefficient value for the fly ash-geogrid interface was the lowest amongst the materials tested i. e 0.28 at 80 kPa, which is greater than the value recommended by JTJ015-91. The finding of the study demonstrated the suitability of using CCR as an economical, environmentally safe and sustainable structural fill material behind RSS. © 2019 Elsevier Ltd

Journal of Cleaner Production

Coal Combustion Residue as Structural Fill Material for Reinforced Soil Structures

This paper describes an experimental and numerical investigation on torsional behaviour of unperforated and perforated cold-formed steel hollow section members. The material characteristics and torsional performance of YSt-310 cold-formed steel square hollow section members (conforming to Indian Standard 4923), were initially studied, experimentally. Effects of size, number, and position of circular perforation on member torsional strength were investigated using validated finite element models, via Abaqus. Additionally, using the FE analysis results, design equations were proposed in Eurocode (EN), Direct Strength Method (DSM) and Deformation Based Method (DBM) formats; for unperforated square hollow section members. The approach is then extended for perforated cases, having circular single and double perforations, using suitable reduction factors, considering effects of both cross-sectional slenderness and perforation size. The proposed design equations were assessed through reliability analysis and were found to be safe for design of cold-formed square hollow sections under torsion. © 2019 Elsevier Ltd

Journal of Constructional Steel Research

Cold-formed steel square hollow members with circular perforations subjected to torsion

Millions of people died due to famines in India in the nineteenth and twentieth centuries; however, the relationship of historical famines with drought is complicated and not well understood. Using station-based observations and simulations, we reconstruct soil moisture (agricultural) drought in India for the period 1870–2016. We show that over this century and a half period, India experienced seven major drought periods (1876–1882, 1895–1900, 1908–1924, 1937–1945, 1982–1990, 1997–2004 and 2011–2015) based on severity-area-duration analysis of reconstructed soil moisture. Out of six major famines (1873–74, 1876, 1877, 1896–97, 1899 and 1943) that occurred during 1870–2016, five are linked to soil moisture drought and one (1943) was not. The three most deadly droughts (1877, 1896 and 1899) were linked with the positive phase of El Ni{\~{n}}o–Southern Oscillation. Five major droughts were not linked with famine and three of those five nonfamine droughts occurred after Indian independence in 1947.

Geophysical Research Letters

Drought and Famine in India, 1870–2016

In this paper, we present the dynamics of bedload transport from two different perspectives. They are the analytical perspective and the turbulence phenomenological perspective. In bedload transport from the analytical perspective, we highlight the systematic advances in the analytical modelling of bedload transport over the decades. These advances are principally classified into three broad foundations, namely, the deterministic foundation, that includes the bed shear stress concept, stream power concept, force balance concept and bedform concept, and the probabilistic foundation and the turbulence phenomenological foundation of bedload transport. The bedload transport from the turbulence phenomenological perspective brings into focus the bedload-induced turbulence phenomenology, including the hydrodynamics of mobile-bed and water-worked bed flows. We also discuss the recent advances in the biofilm-coated bedload transport. Finally, conclusion is drawn, highlighting the major research challenges. © 2019 International Research and Training Centre on Erosion and Sedimentation / the World Association for Sedimentation and Erosion Research

International Journal of Sediment Research

Bedload transport from analytical and turbulence phenomenological perspectives

Bed particle saltation in turbulent wall-shear flow remains an intriguing phenomenon in applied hydrodynamics. In this review, we report the current state of the art of bed particle saltation in turbulent wall-shear flow, highlighting the physical characteristics of bed particle saltation and its mathematical modelling. A critical appraisal of the mechanics of bed particle saltation is presented thorough ample experimental evidence. The salient features of bed particle saltation, encompassing the saltation height, saltation length, particle velocity, saltation duration, particle collision with the bed, particle rotation, particle resting time and particle re-entrainment, are thoroughly discussed. Both the deterministic and computational fluid dynamics approaches in modelling bed particle saltation are summarized, and the subtle role of the hydrodynamic forces is elaborated. The estimation of bedload flux in a fluvial environment, emanating from the mathematical modelling of bed particle saltation, is delineated using different modelling approaches. Finally, the challenges in modelling bed particle saltation are highlighted, and a new look at bed particle saltation is furnished. © 2019 The Author(s) Published by the Royal Society. All rights reserved.

Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences

Bed particle saltation in turbulent wall-shear flow: A review

In this review article, the current status of research on pier scour under waves is presented. This includes a summary of different bridge failure events due to scour, scour mechanism, scour depth predictors under waves, influence of pier shape on scour depth formation, shape of scour hole around piers, and many others. Further, this article describes the scour process, development of scour depth predictors, and the complexity involved in the scour related calculations. Finally, the future scope of research is delineated. © 2019 by the authors.

Fulltext

Water (Switzerland)

Scour around piers underwaves: Current status of research and its future prospect

Developing appropriate experiments to characterize the rutting potential of an asphalt binder will aid in suitable selection of asphalt binders for a location, depending on the prevailing temperature and loading conditions. This study is an attempt to develop a ranking parameter for the high-temperature performance of asphalt binders that can explain the effect of temperature, stress levels, and short-term aging. Six different asphalt binders comprising conventional, warm mix modified, and polymer modified binders were used in the study. A multiple stress creep and recovery (MSCR) test was conducted at 40°C, 50°C, 60°C, and 70°C using four different stress levels of 3.2, 5, 8, and 10 kPa. The test was conducted on unaged and rolling thin-film oven (RTFO) aged conditions. The Arrhenius equation was used to model the variation of unrecoverable creep compliance, Jnr, with temperature at different stress levels. It was found that, irrespective of stress level and aging condition, the Arrhenius equation can be successfully used to model the variation of Jnr with temperature. The activation energy, Ea, in the Arrhenius equation was found to be a useful parameter to explain the rutting characteristics of the asphalt binders. A new ranking parameter Eā/(Jąnr,Maximum Temperature×mą) was defined in the study and it can be successfully used to quantify the high-temperature performance of asphalt binders. An aging index was also proposed using the ranking parameter to explain the effect of short-term aging on the rutting susceptibility of the binders. The comparative analysis of the asphalt binders led to a conclusion that elastomeric polymer modified binder, PMB-S, outperforms all the other asphalt binders in both unaged and aged conditions. It is envisaged that such ranking system will ensure the true behavior of asphalt binders under variation of temperature and load conditions in the pavement. © 2019 American Society of Civil Engineers.

Journal of Materials in Civil Engineering

Development of High-Temperature Ranking Parameter for Asphalt Binders Using Arrhenius Model

Life line structures such as elevated flyovers and rail over bridges should remain functional after an earthquake event to avoid possible traffic delays and risk to general public. Generally, restraining the structure by reducing the degrees of freedom often cause serious damages that occurs during a seismic event through yielding of the structural components. By allowing the structure to rock through uplift using suitable arrangements can be a plausible seismic resilient technique. In this context, this article proposes a novel seismic resilient pile supported bridge pier foundation, which uses elastomeric pads installed at top of pile cap. The effect of pile soil interaction along with ground response analysis is also incorporated in the full bridge model adopted for the study. One dimensional equivalent linear site response analyses were performed to arrive at the amplified/attenuated ground motions along the depth of soil.The seismic performance of the proposed bridge with new rocking isolation concept is compared with existing bridge located in medium seismic zone of India. With the help of non-linear dynamic time history analysis and nonlinear static pushover analysis, the bridge modelled using the proposed novel rocking isolation technique shows good re-centering capability during earthquakes with negligible residual drifts and uniform distribution of ductility demand along the piers of the bridge considered in this study. © 2019 Elsevier Ltd