http://localhost:8081/jspui/handle/123456789/26 Thu, 07 May 2026 21:26:46 GMT 2026-05-07T21:26:46Z http://localhost:8081/jspui/handle/123456789/20480 Title: CRUSTAL VELOCITY STRUCTURE OF NORTHWEST HIMALAYA USING SURFACE WAVE DISPERSION Authors: Kumar, Deepak Abstract: We present a precise 1D crustal and upper mantle velocity structure of the Northwest Himalaya, derived from the combined inversion of Rayleigh and Love wave group velocity dispersion reaching depths of up to 220 km, achieved through the application of Genetic Algorithm. Furthermore, we present a comprehensive 3D isotropic shear wave velocity model of the Indo-Gangetic plain, investigating to depths of up to 100 km, by using Rayleigh wave tomography. The Data are obtained from ~130 Indian and neighboring network broadband seismic stations. We use the dispersion dataset measurement of Rayleigh and Love wave from period 4sec to 100 sec. The study region is partitioned into three clusters of wave paths traversing the Upper Indus Basin, categorized by their epicentral locations. This division allows for a comprehensive investigation into the geological characteristics beneath the western, central, and eastern segments of the Upper Indus Basin (UIB). The analysis reveals a gradual increase in crustal thickness from west to east (~61.8 km, shear wave velocity ~4.6 km/s). The Lithosphere-Asthenosphere Boundary (LAB) is identified at 160 km depth (velocity decrease ~1.6%). A sedimentary cover of ~4 km is observed, with an assumed felsic crust similar to the southern Pamir region, possibly resulting from mafic lower crust loss via lithospheric delamination or gravitational instability. We have presented a 3D shear wave velocity model of the northern Indian-Eurasian collision zone (70°E – 80°E) using Rayleigh group velocity tomography, extending down to 80 km depth. Our study incorporated approximately 8,000 new Rayleigh wave dispersion measurements from 121 seismic broadband stations across regional networks, totaling approximately 20,000 dispersions. The methodology involved a two-step surface wave tomography process followed by regionalization with an 80 km Gaussian correlation length and depth inversion. Our regionalized 2D tomography maps effectively capture well-known geological features. At shorter periods (below 20 seconds), slower velocities observed in the Indo-Gangetic Plain, Indus River valley, and the northern Tarim Basin suggest a thicker basement. Conversely, longer periods reveal distinct velocity anomalies in the Himalayan and Tibetan Plateau regions, indicating thicker crust. Thu, 01 Aug 2024 00:00:00 GMT http://localhost:8081/jspui/handle/123456789/20480 2024-08-01T00:00:00Z http://localhost:8081/jspui/handle/123456789/20336 Title: EFFECT OF URM INFILLS ON SEISMIC PERFORMANCE OF RC FRAME AND FRAME-SHEAR WALL BUILDINGS Authors: Sharma, Mayank Abstract: Unreinforced masonry (URM) infilled reinforced concrete (RC) frames are among the most commonly used structural systems, especially in developing countries such as India. Infills are known to affect the behavior and performance of the RC frames significantly. However, they are ignored during structural design and are considered as dead weight. This work studies the effect of infills on the performance and floor acceleration demands of RC frame and frame-shear wall buildings. Indian seismic codes (IS 1893 : Part 1, 2016; IS 13920, 2016) were updated in 2016. The major changes included the introduction of cracked stiffness modification factors and minimum column-to-beam flexural strength ratio. The first study in this thesis is a parametric study on the effect of infills on the collapse probabilities of RC frames designed for different design code levels. The parameters being varied include the quality, thickness, and aspect ratio of the infills, design code, and number of stories. A total of 33 frames divided into 8 sets are included. Each set includes a bare frame, a bare frame designed using the period of the corresponding infilled frame, a frame with an open ground story, a frame with an open ground story designed for 2.5 times the story seismic forces, and a fully infilled frame. The collapse probabilities are obtained through multiple stripe analysis (MSA) with eight stripes or return periods. Results indicate that the adopted design code has the most significant effect on the collapse performance, followed by the number of stories. The effect of adding infills on the collapse performance of bare frame is negligible to severely negative depending on multiple factors. Most tall buildings in India use a dual system consisting of RC frames and shear walls as their lateral load-resisting system. These RC frame-shear wall buildings are often infilled with URM infills as partition walls. A study is undertaken to estimate the effect of adding infills on the collapse performance of a 25-story RC frame-shear wall building. The bare frame, fully infilled, and open ground story versions of the building are considered. The performance is quantified through the probability of exceedance of collapse prevention (CP) limits for seven Engineering Demand Parameters (EDPs). The ratio of story shear carried by the moment frames to the total story shear is studied at five return periods (approximating five levels of nonlinearity) to comprehend the frame-shear wall interaction in different buildings at different levels of damage. The bare frame-shear wall building has higher probabilities of exceedance for most EDPs indicating that infills have a beneficial effect on the performance. The probabilities of exceedance of different EDPs are similar for the two infilled frame-shear wall buildings (open ground story and fully infilled) indicating that presence of an open ground story doesn’t affect the performance significantly. The effect of URM infills is also estimated on the floor acceleration demands in frame and frame-shear wall buildings. These demands are calculated at five return period to examine the effect of nonlinearity. The observed demands are also compared with the floor acceleration demands specified by major international codes. The shape of observed peak floor spectral acceleration/peak ground acceleration PFSA/PGA profiles is significantly different from that of the corresponding code-specified profiles. For all buildings, the peak floor acceleration/peak ground acceleration (PFA/PGA) profiles specified by IS 16700 (2016) and Eurocode 8 (1998) are significantly conservative. In contrast, the PFA/PGA profile specified by ASCE 7-22 (2022) is non-conservative except in the top few stories. The observed floor response spectra/ground response spectra (FRS/GRS) values decreased with an increase in return period or non-linearity. The FRS/GRS values were higher in the flexible direction of the building. The torsion due to asymmetric infills placement is often unnoticed as infills are usually ignored during the design. The effect of irregular placement of infills is studied in terms of induced torsion and its effect on seismic performance of the RC moment frame buildings. 8-story RC frame buildings are considered with different infills patterns, and designed for modern codes, old codes and only for gravity loads. The performance is compared in terms of probabilities of collapse at MCE, obtained from MSA conducted at five stripes. The adverse effects of presence of infills generally overshadow the torsion introduced due to asymmetric infill layout leading to consistently poor performance of buildings with more infilled frames. At higher return period, most of the building eccentricity is lost upon yielding of infills. The effect of asymmetric placement of infills is also studied on the floor acceleration demands in RC frame buildings. In addition to the infilled buildings having stiffness and mass eccentricities in one and both directions, a bare frame building, and a fully infilled building are also considered for comparison purposes. The floor acceleration demands are estimated at five return periods (representing different levels of nonlinearity). The eccentricity along one direction also led to a difference in acceleration demands at flexible corner (FC) and geometric center (GC) along the other principal direction. Interestingly, the difference in floor acceleration demands at FC and GC in the case of bi-eccentric building was relatively less than the difference in the case of uni-eccentric building. Fri, 01 Mar 2024 00:00:00 GMT http://localhost:8081/jspui/handle/123456789/20336 2024-03-01T00:00:00Z http://localhost:8081/jspui/handle/123456789/20335 Title: SEISMIC HAZARD AND RISK ASSESSMENT OF NORTHEAST INDIAN REGION-A PROBABILISTIC APPROACH Authors: Lallawmawma, C. Abstract: Earthquakes are deadly natural disaster that have affected many people in recent decades. Efforts to reduce their impact have become increasingly focused in developed and developing countries. Despite advances in scientific knowledge, accurately predicting earthquakes remains challenging. However, seismic hazard analysis can be used to forecast future ground shaking for specific or multiple locations. The northeast India region is highly seismically active and contains several distinct tectonic features. Despite improvements in building codes and preparedness, mortality rates are still alarming, especially in areas with vulnerable building construction practices. Conducting seismic hazard and risk assessments is crucial in predicting potential losses and assisting local authorities in formulating effective disaster management plans. Previous seismic hazard studies in the region have mainly focused on areal seismic sources, the dimensions and boundaries of which generally remain subject to personal experience and judgment. For this purpose, the study aims to evaluate seismic hazard in northeast India using a smoothed gridded seismicity model, areal source and fault zone models, and estimate seismic risk in Mizoram, a region with limited attention in previous studies. The primary objectives of this study are to conduct a Probabilistic Seismic Hazard Assessment (PSHA) of northeast India and estimate seismic risk in Mizoram. The study is divided into three major parts to achieve the objectives and presented as contributing chapters in the thesis. The first part is to conduct a PSHA of northeast India considering three seismic source models, i.e., areal sources, fault zone sources, and a smoothed gridded seismicity model. The study area covers the region between 87°–98° E longitude and 20°–30° N latitude. The region has been divided into six areal source zones; twenty-eight identified fault sources have been modeled as fault zone source models, while the gridded seismicity model has been modeled as a point source model. Seismicity parameters have been calculated for each source model using a complete (time and size) earthquake catalog treated for homogenization and declustering. Five Ground Motion Prediction equations (GMPEs) for the active shallow region and three GMPEs for the Indo-Burma subduction zone have been used to evaluate seismic hazards. Hazard assessment has been conducted at the reference rock condition (Vs30 = 760 m/s). A logic tree framework has been implemented in source models and GMPEs to account for uncertainties. Peak Ground Acceleration (PGA) and Spectral Acceleration (SA) have been estimated for various cities in the northeastern states, considering a 2% and 10% Probability of Exceedance (PoE) in 50 years. Hazard curves and uniform hazard spectra (UHS) have also been generated. The seismic hazard results have been used to develop disaggregation plots to quantify the contributions of seismic hazard in terms of magnitude and distance combination. The seismic hazard maps generated from the study indicate a range of PGA values varying from 0.11g to 0.43g for a 10% PoE in 50 years. This shows spatial variability in ground shaking intensity across different locations within the study area. Some areas have lower PGA values, while others have higher PGA values compared to the estimates provided by the existing building code. The comparison of the estimated hazard values with other studies showed some variations, which can be attributed to differences in earthquake catalogs, seismic activity input parameters, and source models used. These factors are crucial in influencing hazard estimation. Imphal stands out with the highest PGA level of 0.40g at a 10% PoE among the UHS developed for the seven cities. This is due to the hazard contribution from two specific seismic sources: the Churachanpur Mao Fault and the eastern subduction zone. The highest hazard levels are observed in eastern Manipur, Mizoram, southern Nagaland, and western Arunachal Pradesh, close to the Indo-Myanmar region and Himalayan thrust. Wed, 01 May 2024 00:00:00 GMT http://localhost:8081/jspui/handle/123456789/20335 2024-05-01T00:00:00Z http://localhost:8081/jspui/handle/123456789/20293 Title: STATIC AND SEISMIC BEHAVIOR OF A LATERALLY LOADED PILE IN COHESIONLESS SOIL SLOPES Authors: Reddy, Alla Kranthikumar Abstract: In recent years, rapid infrastructure development has led to an increase in the construction of high-rise buildings, bridges, wind chimneys, transmission towers, and offshore structures. These complex structures require pile foundations that can support both vertical loads, as well as lateral loads from the superstructures. Hence, the design of pile foundations must consider the lateral loads in addition to vertical loads to ensure the safety and cost-effectiveness of the structures. Further, the construction of these structures near slopes has intensified due to the scarcity of level ground. As a result, understanding the behavior of laterally loaded piles near slopes has become a key interest in pile foundation design. Pile-soil interaction in level grounds is complex, and presence of sloping ground adds intricacy to lateral load behavior. Moreover, the occurrence of earthquakes worldwide has significantly increased, highlighting the need to carefully design pile foundations on sloping grounds considering both static and seismic loads. A comprehensive review of the existing literature on laterally loaded piles on sloping ground reveals a dearth of research on sandy soil slopes. Most of the available studies often overlook the influence of edge distance and other important parameters on the laterally loaded pile behavior in soil slopes under static conditions. Further, research related to dynamic behavior of piles primarily focused on piles in liquefiable sandy slopes. There is a lack of comprehensive studies addressing the dynamic behavior of piles in non-liquefiable sandy slopes, accounting for both the kinematic and inertial effects. Consequently, a complete understanding of the behavior of piles situated in dry sandy soil slopes, considering static and seismic conditions, is currently lacking. To address the existing research gap, a comprehensive investigation was undertaken using the finite element software, PLAXIS 3D, to analyze the behavior of piles situated in sandy soil slopes. This study has encompassed both static and seismic loading conditions. In the static case, the lateral load behavior of piles was examined under both free head and fixed head conditions. A parametric analysis was conducted, encompassing various pile-soil slope parameters that affect the lateral load behavior of piles in slopes. Furthermore, the influence of pile location with reference to slope crest and direction of loading was also investigated. Prior to the parametric analysis, mesh convergence studies were performed to assess the impact of the soil domain and mesh element size on numerical simulations. Moreover, validation was carried out by comparing the obtained results with previous centrifuge test findings, ensuring the accuracy of the step-bystep modeling and selection of material models. Sat, 01 Jun 2024 00:00:00 GMT http://localhost:8081/jspui/handle/123456789/20293 2024-06-01T00:00:00Z