Department of Civil & Infrastructure Engineering

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IIT Jodhpur

Pile foundations often suffer excessive bending stresses induced by the vibra-tory deformations and the corresponding interactions of the seismic waves. Such soil-pile mutual interaction is termed as kinematic interaction and is crucial in case of liquefiable soils as additional stresses may be induced on the pile. This article aims to investigate the kinematic response of a single pile and 2×2 pile group embedded in liquefiable soil. Dynamic beam on nonlinear Winkler foundation approach (BNWF) has been adopted herein, incorporating the liquefaction behavior of soil with the hyper-elastic bilinear model. First, the BNWF model is validated against the centrifuge results. A liquefiable soil profile located in a highly active seismic region of India has been considered. Nonlinear effective stress ground response analyses were performed to account for the pore pressure generation using the experimentally derived dynamic soil properties. Seismic analysis has been performed through nonlinear time history analysis on the chosen pile configurations. An abrupt contrast in the peak bending moment has been observed at the vicinity of liquefied and nonliquefied interfaces due to the sharp stiffness contrast. The pile group showed significantly better seismic performance in terms of reduced peak displacements and bending moments compared to the single pile response, in case of liquefiable soils. © 2019 Associazione Geotecnica Italiana, Rome, Italy.

World University root node

Earthquake Geotechnical Engineering for Protection and Development of Environment and Constructions- Proceedings of the 7th International Conference on Earthquake Geotechnical Engineering, 2019

Kinematic response of pile foundations in liquefiable soils

An experimental programme to study the residual mechanical strength of Tata Structura-YSt 310 cold-formed steel square and rectangular tubular sections (conforming to Indian Standard 4923) after being exposed to elevated temperature is described in this paper. First, the coupon specimens extracted from the flat regions are exposed to pre-determined elevated temperature in the range ~ 300–800 °C, and then the residual mechanical properties and hardness value were estimated at ambient temperature after natural air cooling. The results from the experimental programme are reported in this paper in the form of post-firestress-strain curves and associated basic material properties (e.g. elastic modulus, proof stresses, tensile strength, percentage elongation at fracture, Ramberg-Osgood material parameters etc.) as well as surface hardness values. The test results showed that most post-fire mechanical properties are appreciably different from ambient temperature material properties when exposed to a temperature higher than ~400 °C; whilst elastic modulus appears to remain unaffected even when the exposed temperature is up to ~800 °C. A near linear relationship of post-fire material strengths and hardness value was observed. Two sets empirical equations are proposed separately to predict the residual post-fire reduction factors based on the i)current experimental results of Tata Structura-YSt 310 cold-formed steel, and ii) cold-formed steel of various grades presently available in the literatures. © 2018 Elsevier Ltd

Journal of Constructional Steel Research

Post-fire mechanical properties of YSt-310 cold-formed steel tubular sections

It is necessary to understand the hydrological processes undergoing at small segments in order to apprehend the complex large river systems and this can be achieved by application of hydrological models. This study aims to check the applicability of soil and water assessment tool (SWAT) model over the Kharun River Basin, Chhattisgarh, India. The limitation of data at proper scales is the major problem that hinders research on this area. The meteorological data were collected from climate forecasting system reanalysis (CFSR) database for 1994–2014. The SWAT simulations generated runoff, which was auto-calibrated with the observed values through SWAT-CUP. Generalized uncertainty likelihood estimation (GLUE) optimization approach was used for sensitivity analysis of various parameters during auto-calibration. The results reveal for a moderate correlation between the observed and modelled values at daily time scale i.e. the Nash-Sutcliffe efficiency and R2 values are close to 0.5. This highlights the fact that model application needs to be carried out carefully with processed and reliable data sets. Also, some of the popular models may as well be not suitable for few basins with multiple complexities. The possible reasons for such moderate performance of the model are also discussed. This work will be helpful to the decision makers for better planning and management of the basin.

World Environmental and Water Resources Congress 2019: Watershed Management, Irrigation and Drainage and Water Resources Planning and Management - Selected Papers from the World Environmental and Water Resources Congress 2019

Application and performance assessment of SWAT hydrological model over Kharun river basin, Chhattisgarh, India

AGU Fall Meeting 2019

A two-fold rise in the frequency of severe drought in South Asia under a warming climate

AGU Fall Meeting Abstracts 2019, H23H

On the causes and severity of the 2016-17 South India drought

This article develops a fully coupled hydro-thermo-mechanical formulation based on the direct stiffness method for analysis of steel and reinforced concrete structural space frames. The superiority of the developed formulation lies in developing the direct stiffness method for fire analysis, which enables use of a much coarser spatial mesh when compared to existing fire analysis frameworks. Effects of temperature-dependent material properties, damage due to fire and pore pressure, nonlinear thermal gradients, and large deformations of structural members are directly integrated into the stability and bowing functions in the construction of the member stiffness matrix. This alleviates the need to perform element-level numerical quadrature, typically required by all existing finite element–based approaches. Full coupling between the pore pressure, thermal and mechanical solvers is considered through a two-level spatial discretization strategy with a staggered scheme for the numerical solution procedure. Five numerical examples are presented to demonstrate the accuracy and efficacy of the developed formulation in analysis of steel and reinforced concrete structural members and frames. © The Author(s) 2018.

Advances in Structural Engineering

Fully coupled multi-physics nonlinear analysis of structural space frames subjected to fire using the direct stiffness method

Changes in extreme precipitation due to climate change often require the application of methods to bias correct simulated atmospheric fields, including extremes. Most existing bias correction techniques (i) only focus on the bias in the mean value or on the extreme values separately, and (ii) exclude zero values from analysis, even though their presence is significant in daily precipitation. We developed a copula-based bias correction scheme that is suitable for zero-inflated daily precipitation data to correct the bias in mean as well as in extreme precipitation at any specific statistical quantile. In considering the whole of Germany as a test bed, the proposed scheme is found to work well across the entire study area, including the German Alpine regions. The joint distribution between observed and regional climate model (RCM)-derived precipitation is developed through copulas. In particular, the joint distribution is modified to make it discrete at zero in order to account for zero values. The benefit of considering zero precipitation values is revealed through the improved performance of bias correction both in the mean and extreme values. Second, the quantile that best captures the bias (whether in the mean or any extreme value) is determined for a specific location and varies spatially and seasonally. This relaxation in selecting the location-specific optimal quantile renders the proposed methodology spatially transferable. By acknowledging possible changes in extreme precipitation due to climate change, the proposed scheme is expected to be suitable for climate change impact assessments for extreme events worldwide. © 2019 American Meteorological Society.

Journal of Hydrometeorology

Bias correction of zero-inflated RCM precipitation fields: a copula-based scheme for both mean and extreme conditions

Interaction between meteorological and hydrologic processes is challenging to model owing to their high spatio-temporal variability. The understanding of their associations can help to ensure future fresh water security with changing climate. In this study, due to continuously evolving nature of these interactions, the hydrological and meteorological variables are studied on wavelet component level. Multi-Resolution Stationary Wavelet Transformation (MRSWT) is used to transform the independent (climatic variable) and dependent (hydrological variable) time series into their components. The components of the dependent time series are modeled using a kernel-based auto-regressive (AR) model for separating their memory part. The residuals are hypothesized to be the effect of interaction of predictor variables and thus, are modeled using the MRSWT components of meteorological variables in an auto-regressive model with exogenous inputs (ARX). Finally, the predicted residuals (effect of climatic variables) are added to the component estimated by kernel-based AR estimator (memory of dependent series components) to obtain the predicted components of the dependent hydrologic variable, which are then inverse-transformed to obtain the predicted dependent hydrologic variable. The developed hybrid Wavelet-ARX is found to capture the information about relationship between synthetically generated data better than a simple ARX model. The model is then applied to predict total monthly rainfall over Upper Mahanadi Basin and is found to effectively extract the information from the poorly associated hydro meteorological variables. While the potential of Wavelet-ARX is found to be impressive for hydro meteorological applications, additionally, discarding some climatic inputs on the basis of their relative importance may lead to better prediction by the developed model. The developed model is suitable for extracting climatic forcings and is desirable in a changing climate. © 2019 Elsevier B.V.