Showing papers by "T. G. Sitharam published in 2022"

Printability, Thermal and Compressive Strength Properties of Cementitious Materials: A Comparative Study with Silica Fume and Limestone

Abstract: Over the past decade, 3D printing in the construction industry has received worldwide attention and developed rapidly. The research and development of cement and concrete products has also become quite well-established over the years, while other sustainable materials receive considerably lower attention in comparison. This study aims to investigate the influence of the two most commonly used sustainable cementitious materials i.e., silica fume and limestone powder, on printability, thermal and mechanical properties of fly ash–Portland cement blends. Ternary blends containing Portland cement, fly ash and silica fume or limestone powder are prepared, whereas phase change material (PCM) is introduced to improve the thermal behavior. Based on the rheological properties and concurrent 3D concrete printing, improved buildability of the modified mixtures is linked to their static yield stress. Anisotropic mechanical properties are observed for 3D printed specimens, while cast specimens exhibit a maximum 41% higher compressive strength due to better material compaction. It is clear from the results that addition of silica fume and limestone powder ranged from 5% to 10%, reducing the anisotropic mechanical properties (maximum 71% and 68% reduction in anisotropic factor, respectively) in the printed specimens. The PCM addition ranged from 5% to 10% and improved thermal performance of the mixtures, as measured by a decrease in thermal conductivity (9% and 13%) and an increase in volumetric heat capacity (9% and 10%), respectively. However, the PCM-containing mixtures show around 29% reduction in compressive strength, compared to the control specimen, which necessitates new material design considering matrix strengthening methods.

Joint Time Frequency Analysis Based Synthesis of Acceleration-Time History and Response Spectra for Japanese Earthquakes

Abstract: Time–Frequency Analysis (TFA) techniques help to obtain the ideal time and frequency occurrence characteristics of earthquake motion confined in a seismic recorded signal. Time-histories from recording stations in Japan has been adopted in the present analysis, considering a large number of available data. The seismograms were transformed using Gabor transform, a Linear Joint TFA method, to assess their frequency content by generating their Gabor coefficients. Average Gabor coefficients were estimated for recorded seismograms within a magnitude range of 5.5–6.0 and hypocentral distances ranging from 0 to 50 km. The estimated average Gabor coefficients were used to synthesize a generalized acceleration-time history for the specific distance and magnitude ranges using Gabor Expansion, without compromising the frequency content of the waves. Additionally, it is demonstrated that the response spectra of the synthesized signal and the original signal match very well. These response spectra will be valuable for the nonlinear investigation of structures in this region.

Site response analysis of liquefiable soil employing continuous wavelet transform

Abstract: Propagation of the earthquake motion towards the ground surface alters both the acceleration and frequency content of the motion. Acceleration time record and Fourier amplitude spectrum of the motion reveal changes in the acceleration and frequency content. However, Fourier amplitude spectrum fails to give frequency-time variation. Wavelet transform overcomes this difficulty. In the present study, site response analysis of a liquefiable soil domain has been investigated employing wavelet transform. Three earthquake motions with distinct predominant frequencies are considered. It is revealed that the moment soil undergoes initial liquefaction, it causes a spike in the acceleration time history. Frequency of the spikes is found to be greater than the predominant frequency of the acceleration-time history recorded at the ground surface from the analysis. Interestingly, the spikes belong to the sharp tips of the shear stress-shear strain curve. Immediately after the spike, acceleration deamplification is observed. Post-liquefaction deamplification (filtering) of the frequency components is also observed.

Assessment of Earthquake Recurrence for North India and Surrounding Region Using Probabilistic Models

Abstract: AbstractThe northern part of India is one of the seismically active regions of the world, which lies near the plate boundary region of Indian plate and Eurasian plate. The continuous tectonic movement between Indian plate and Eurasian plate accumulates lots of strain energy in the plate boundary region and this energy may come out in near or far future generating big earthquakes in this region. The 25thApril 2015 Nepal earthquake (Mw 7.8) is one of the outcomes of such huge stored strain energy. So, in the attempt of minimizing loss of lives and properties, this paper presents probabilistic models for forecasting of earthquakes of magnitude (Mw) ≥ 7.0 in North India (NI) and surrounding region. In this present study, three probabilistic models namely Weibull, Gamma and Lognormal probabilistic models were used to estimate the probability of occurrence of earthquake Mw ≥ 7.0 using an earthquake catalogue 1900–2016. The goodness of models was assessed by the logarithmic likelihood function (ln L). As per the results, the Weibull models shows highest probability of occurrence whereas the lognormal model shows the lowest probability of occurrence. The estimated conditional probability reaches 0.999 after a time interval of 11, 13 and 15 years for Weibull, Gamma and lognormal Distribution respectively from the last earthquake of 2015. This means by the year 2026, 2028 and 2030 by Weibull, Gamma and lognormal model respectively will achieve a conditional probability of 99.9% in and around the present study area.KeywordsConditional probabilityEarthquake recurrenceMaximum likelihood estimation (MLE)Probability modelsRecurrence interval

Stability Analysis of Tailings Dam Using Finite Element Approach and Conventional Limit Equilibrium Approach

Abstract: The probability of failure in tailings dam is generally found to be much greater than the conventional water retaining dams. Slope instability is one of the major reasons, contributing more often to the failure of these tailings dam. Due to this reason, the stability of tailings dam has drawn much attention as significant numbers of tailings dam’s failure have been reported worldwide in the recent years. The present work focuses on evaluating the stability of existing tailings dam by using finite element method (FEM) as well as conventional limit equilibrium methods (LEMs) under static loading conditions. Shear strength reduction (SSR) technique is incorporated (by using 2D finite-element based package RS2) in order to observe the potential modes of failure. Further, Rocscience SLIDE-2D is utilised to evaluate the stability of dam embankments by LEM. The results obtained from the analysis utilizing both LEM and FEM are compared in terms of their global factor of safety (FOS) and strength reduction factor (SRF) respectively. Further, an attempt is made to explore the stability of different types of tailings dam, based on their method of construction (i.e., upstream (U/S) method and downstream (D/S) method). The results obtained from LEM and FEM are found be in good agreement with each other. It is observed that the FOS and SRF values decrease as the height of embankment is raised. In addition, the failure surface is found to be circular in FEM for most of the critical slopes, which supports the assumptions of circular slip surface considered in LEMs based analysis. In addition, D/S slope is found to be more susceptible to failure than the U/S slope, for both U/S and D/S methods of construction.