http://dspace.dtu.ac.in:8080/jspui/handle/123456789/42 2026-07-01T23:49:40Z 2026-07-01T23:49:40Z SINGH, ISTUTI SAHU, A. K. (SUPERVISOR) http://dspace.dtu.ac.in:8080/jspui/handle/repository/22943 2026-06-25T05:08:34Z 2025-12-01T00:00:00Z

Title: LOAD DEFORMATION BEHAVIOUR OF STONE COLUMN IN EXPANSIVE SOIL REINFORCED WITH GEOSYNTHETICS Authors: SINGH, ISTUTI; SAHU, A. K. (SUPERVISOR) Abstract: The present study investigates the improvement of weak soils using granular columns, with emphasis on the role of geosynthetic encasement and iron dust inclusion in enhancing load-bearing capacity and reducing settlement. Soft soils often exhibit excessive compressibility and inadequate strength, making them unsuitable for direct foundation support. To address these challenges, granular columns are widely employed; however, their efficiency depends on factors such as column arrangement, diameter, and confinement. This research systematically explores the behavior of both single and group columns under different conditions to identify optimum configurations for practical applications. The primary objectives of the study were to evaluate the load–deformation behaviour of ordinary and geosynthetic-encased stone columns in expansive soil, to investigate the influence of column configuration, encasement material, and iron dust stabilization on bearing capacity and settlement characteristics, and to identify the most efficient ground improvement system for expansive soils. The study employed both experimental and numerical methods. Laboratory model tests were conducted on single columns of diameters 50 mm and 70 mm, as well as group columns arranged in triangular, square, and hexagonal patterns with varying spacing-to-diameter (s/d) ratios. Both ordinary and encased stone columns were examined, using geotextile and geogrid as encasement materials. The stone column mix was prepared using stone dust, fly ash, cement, and iron dust to enhance column strength. Tests were performed under monotonic vertical loading, and settlements were measured up to 50 mm. The experimental results were further validated using numerical modeling in PLAXIS 3D. The findings revealed that untreated clay beds had very low load capacity (5.9 kN at 50 mm settlement). Single ordinary stone columns improved the load resistance, with 70 mm end-bearing columns carrying 7.2 kN and floating columns 6.5 kN. Encased single columns showed further gains, with geotextile-encased end-bearing viii columns sustaining up to 8.15 kN, about 38% higher than untreated clay. In group configurations, the triangular pattern consistently gave the best performance, followed by square and then hexagonal arrangements. Geosynthetic encasement enhanced group behavior significantly, with geotextile generally outperforming geogrid due to better fines retention and hoop stress mobilization. The inclusion of iron dust in the column mix further reduced settlement and improved strength, particularly in group columns. Overall, the study concludes that the triangular arrangement of group stone columns, encased with geotextile or geogrid and stabilized with iron dust, provides the most efficient configuration. This system achieves the highest load-bearing capacity and the least settlement, demonstrating its practical applicability for soft soil improvement. The research contributes valuable insights into the design and optimization of granular column foundations and establishes the benefits of combining geosynthetic encasement with stabilizing additives. Additionally, the experimental program was conducted using single columns of diameters 20 mm, 30 mm, and 50 mm, along with group columns arranged as double columns along the mould diameter and triangular columns with a spacing to-diameter ratio of 1. Tests were performed with and without encasement using geotextile and geogrid to assess their relative performance. Additionally, iron dust was introduced as a stabilizing additive to study its effect on settlement and strength. Load–settlement responses were recorded and analyzed to evaluate the comparative performance of each configuration. The results revealed that single columns performed best when encased with geotextile, with the 30 mm diameter column providing maximum load capacity. Group column behavior was influenced more by arrangement, with triangular patterns offering superior settlement resistance compared to double columns. Among the encasement materials, geogrid provided better confinement in group columns, whereas geotextile was more effective for single columns. The inclusion ix of iron dust consistently enhanced overall performance, lowering settlements and increasing load capacity, particularly in group column arrangements. It is concluded that the most efficient configuration for ground improvement in weak soils is the triangular group arrangement of granular columns encased with geogrid and stabilized with iron dust. This combination delivers the highest load bearing efficiency and the least settlement, offering a practical and effective solution for foundation support in soft soils. The findings provide valuable insights into the design and application of granular columns, contributing to the advancement of ground improvement techniques in geotechnical engineering.

2025-12-01T00:00:00Z THAKUR, AKASH PAL, SHILPA ( SUPERVISOR) http://dspace.dtu.ac.in:8080/jspui/handle/repository/22936 2026-06-25T05:07:24Z 2026-05-01T00:00:00Z

Title: EXPERIMENTAL EVALUATION OF SEISMIC RESPONSE OF NON STRUCTURAL COMPONENTS IN RC FRAMES Authors: THAKUR, AKASH; PAL, SHILPA ( SUPERVISOR) Abstract: Non-structural elements (NSEs) such as cable trays, pipelines, HVAC systems, and suspended utilities are highly vulnerable during earthquakes and play an important role in maintaining building functionality after seismic events. Recognizing the importance of seismic safety of utility systems, IS 1893 introduced new provisions for “Architectural Elements and Utilities (AEUs)” in Indian seismic design practice. However, limited experimental validation is available for these newly introduced provisions. The present study investigates the seismic behaviour of cable tray systems installed in a structural frame model subjected to shake table excitation. Cable trays with rigid and flexible support configurations were installed at different floor levels, and acceleration response was measured at the base, floor slabs, and cable tray locations under excitation frequencies ranging from 0.5 Hz to 12 Hz. Experimental results showed significant floor acceleration amplification at upper floors, with maximum Peak Floor Acceleration (PFA) of 1.5g observed at the third floor. Resonance behaviour was observed between 6.5 Hz and 8.5 Hz, resulting in sudden increase in cable tray acceleration response. The amplification factor increases significantly with elevation, showing a 50.38% rise from the 1st to the 2nd floor and a further 25.00% rise from the 2nd to the 3rd floor, resulting in an overall increase of 87.97% from the 1st to the 3rd floor. The flexible support system shows the highest amplification increase at the 1st floor (81.82%), while the increase at the 2nd and 3rd floors is approximately 53–59% compared to the rigid support system. Comparative analysis between experimentally obtained seismic forces and codal force predictions based on Draft IS 1893 and ASCE 7 indicated that actual seismic demand exceeded equivalent static codal predictions near resonance conditions. Where experimental force exceeded the IS 1893 value approximately 71%. The study highlights the importance of considering floor amplification, resonance effects, and support flexibility in seismic design of utility systems. The findings of the study contribute toward improved understanding of seismic behaviour of non-structural utility systems and provide practical design recommendations for seismic anchorage and support systems in RC buildings.

2026-05-01T00:00:00Z GUPTA, PRANJAL PAL, SHILPA (SUPERVISOR) http://dspace.dtu.ac.in:8080/jspui/handle/repository/22935 2026-06-25T05:07:15Z 2026-05-01T00:00:00Z

Title: STRUCTURAL INTEGRITY ASSESSMENT FOR LIFE EXTENSION AND RETROFITTING OF AGING OFFSHORE PLATFORMS Authors: GUPTA, PRANJAL; PAL, SHILPA (SUPERVISOR) Abstract: Hydrocarbons continue to play an important role in meeting global energy demand. In India, offshore oil and gas facilities, especially in the western offshore region, contribute significantly to domestic production and energy security. However, many fixed jacket platforms in fields such as Mumbai High are now operating beyond their actual design life and are exposed to long-term deterioration due to wave loading, corrosion, fatigue, accidental damage, and changing operational requirements. These factors make periodic reassessment and re-certification essential to ensure the continued structural integrity and safe operation of aging offshore platforms. The present study focuses on the structural reassessment of an existing fixed jacket type offshore platform based on the recommendations of the American Petroleum Institute (API) for life extension assessment. Site-specific metocean data for the Gulf of Kutch, including wave, wind, and current conditions corresponding to both operating and extreme storm environments, are considered during the analysis. A global linear in-place structural analysis is performed using SACS v24 to evaluate the adequacy of jacket members and tubular joints under combined operational and environmental loading conditions. Member and joint utilization checks are performed in accordance with API RP 2A, 22nd Edition, Working Stress Design, 2014 provisions to identify overstressed structural components. For loading conditions where the platform does not meet the prescribed acceptance criteria, a nonlinear ultimate strength assessment is performed using static pushover analysis to capture the actual structural response under extreme environmental loading. Incremental wave loading is applied until structural collapse to investigate the failure sequence, redistribution of internal forces, and ultimate collapse behaviour of the jacket system. The Reserve Strength Ratio (RSR), also referred to as the Collapse Load Factor (CLF), is evaluated to determine the residual strength and redundancy of the platform. The study also examines strengthening and retrofitting techniques for overstressed subsea tubular joints, which remain one of the major challenges in rehabilitation of aging offshore structures. Retrofit schemes using ring stiffeners and friction-grip clamp systems are evaluated for strengthening deficient joints and facilitating iv member replacement without extensive modification to the existing structure. To investigate local joint behaviour in detail, Component-Based Finite Element Analysis (CBFEA) is carried out using IDEA StatiCa 26.0. Detailed finite element models of tubular joints incorporating ring stiffeners and clamp arrangements are developed to evaluate stress distribution, load transfer mechanisms, and structural performance under applied loading conditions. The results of the study indicate that the adopted reassessment and strengthening approach improves both global and local structural performance of the aging jacket platform. From the in-place analysis, 20 tubular joints are found overstressed under extreme storm loading. After grout filling, most of the joints meet the unity check requirement and for remaining critical joints retrofitting procedures are performed. The pushover analysis shows adequate global reserve strength, with the minimum RSR obtained as 1.80 against the required value of 1.60, and the maximum RSR obtained as 3.20. For the proposed mechanical friction-grip clamp, all IDEA StatiCa checks remain within allowable limits, with maximum bolt utilization of 87.2%, weld utilization of 76.8%, and first buckling factor of 43.85. The ring stiffener model also shows improvement in local stress distribution, with the equivalent stress in members reducing from 355.3 MPa to 286.9 MPa. These results confirm that targeted retrofitting using ring stiffeners and friction-grip clamp systems can improve the residual capacity and support the life extension of the existing offshore jacket platform.

2026-05-01T00:00:00Z PORE, VISHNU Robert, B.R.G. (SUPERVISOR) http://dspace.dtu.ac.in:8080/jspui/handle/repository/22932 2026-06-25T05:06:49Z 2026-05-01T00:00:00Z

Title: COMPARATIVE STUDY OF STATIC AND DYNAMIC ANALYSIS OF RCC STRUCTURES UNDER INDIAN SEISMIC CONDITION Authors: PORE, VISHNU; Robert, B.R.G. (SUPERVISOR) Abstract: The increasing occurrence of earthquakes in different seismic regions has emphasized the necessity for reliable structural analysis methods in reinforced cement concrete (RCC) buildings. This study presents a comparative evaluation of static and dynamic analysis techniques for RCC structures under Indian seismic conditions. The goal of the research is to explore the structural behavior, seismic performance, and response characteristics of RCC buildings when subjected to earthquake forces as specified in Indian seismic design provisions, primarily based on Bureau of Indian Standards code recommendations such as IS 1893 and IS 456. In this research, multi-storey RCC structures are modeled and analyzed using ETABS. Pushover analysis and time history analysis, are used to assess the seismic response of the structures. Important response parameters such as storey displacement, storey drift, base shear, are compared for seismic zones IV . This dissertation presents a detailed comparative study of the pushover analysis of RCC structures with rigid joints under Indian seismic conditions. The primary aim of the study is to evaluate, compare, and interpret the nonlinear seismic behavior of multistorey RCC buildings by considering key performance parameters such as base shear, terrace displacement. The buildings are designed in accordance with the provisions of IS 456:2000 for reinforced concrete design and IS 1893 (Part 1):2016 for earthquake-resistant design of structures. The seismic performance is assessed using the concepts of performance-based seismic design as defined in international guidelines such as FEMA 356 and ATC-40. For the purpose of analysis, three-dimensional numerical models of RCC buildings are developed using ETABS software. Gravity loads and seismic loads are applied as per Indian Standard codes. Nonlinear hinge properties are assigned to beams and columns to simulate realistic material behavior under increasing lateral loads. The pushover analysis is carried out by applying incremental lateral load patterns in both principal horizontal directions until the target displacement or collapse mechanism is achieved. A comparative assessment of different structural configurations is performed to investigate their influence on seismic behavior. The study highlights how changes in stiffness, strength, and ductility affect the overall performance of RCC structures. Storey-wise displacement, drift ratios, and plastic hinge distribution patterns are critically examined to identify vulnerable zones and potential failure mechanisms. ix Special emphasis is placed on understanding the nonlinear response characteristics of rigid jointed RCC frames, which are extensively used in Indian construction practice. The results obtained from the analysis clearly demonstrate that PA is highly effective in capturing the progressive damage behavior and post-elastic response of RCC buildings, which cannot be adequately assessed through linear static or dynamic methods. The study reveals that the formation and progression of plastic hinges follow distinct patterns that govern the ultimate collapse mechanism of the structure. It is observed that structures designed strictly as per code provisions still exhibit significant nonlinear deformations under severe seismic excitation, emphasizing the importance of performance-based evaluation. The outcomes of this study provide valuable insights into the seismic performance of RCC buildings under Indian seismic conditions and confirm the reliability of pushover analysis as a practical and efficient tool for seismic evaluation. The findings of this research are expected to assist structural engineers in identifying seismic deficiencies, improving structural configurations, and adopting safer design practices. The study also highlights the importance of incorporating nonlinear analysis procedures into routine seismic design and assessment workflows to enhance the safety, resilience, and sustainability of reinforced concrete structures in earthquake-prone regions of India.

2026-05-01T00:00:00Z