International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 12 Issue: 05 | May 2025
p-ISSN: 2395-0072
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“Analyzing the Effect of Terrain Gradient on Seismic Response on SMRF Structures” Aman Shah1, Aakash Suthar2 1M.Tech Student, Department of Structural Engineering, L.J. University, Ahmedabad, Gujarat, India. 2Assistant Professor, Structural Engineering Department, L.J. University, Ahmedabad, Gujarat, India.
---------------------------------------------------------------------***--------------------------------------------------------------------Abstract -This study presents a comprehensive seismic performance assessment of a G+12 Special Moment Resisting Frame (SMRF) structure located on sloping terrains, utilizing ETABS for structural analysis. The investigation encompasses four terrain slopes 0°, 20°, 45°, and 60° across three soil classifications: hard, medium, and soft, under seismic zones III and IV. Critical response parameters including story displacement, story drift, stiffness and strength irregularities, mass irregularity, torsional irregularity, diaphragm behavior (rigid vs. flexible), and mode shapes were evaluated to understand the influence of topographical and geotechnical variations on seismic behavior. The results show that increasing slope inclination and decreasing soil stiffness notably increase seismic demands. Structures situated on steeper slopes and softer soils exhibited greater lateral displacements, higher torsional irregularities, and more complex mode shapes, indicating a higher vulnerability to dynamic loading. Rigid diaphragm systems were found to enhance overall structural stability by reducing deformation and controlling inter-story drift. This study emphasizes the significant impact of slope geometry, soil flexibility, and diaphragm type on the seismic response of multistory structures. The findings reveal the limitations of traditional design assumptions based on flat ground and highlight the need for slope-adaptive structural strategies. Such approaches are essential for ensuring the safety and performance of structures in seismically active regions with irregular topography
increasingly scarce, urban development has started to expand into hilly and mountainous areas. This trend has led to the construction of mid- to high-rise buildings on sloped terrains, introducing complex engineering challenges that go beyond those faced in traditional flatland construction. Buildings located on sloping ground differ significantly in their behavior and design compared to those built on flat sites. The terrain requires stepped or terraced foundations, creating variations in elevation and support conditions across the base of the structure. This unevenness affects both the vertical load path and the distribution of stiffness throughout the building’s footprint. Additionally, sloped terrain can lead to nonuniform mass distribution due to differences in story height, column length, and the overall shape of the building envelope. These irregularities can greatly impact the building's seismic response, resulting in complex interactions between lateral and torsional movements and increasing the likelihood of structural damage during earthquakes. Seismic design codes typically identify certain structural irregularities—such as stiffness, strength, mass, and torsional irregularities—as critical factors that influence dynamic performance. These characteristics are often more pronounced in hillside buildings, making them particularly vulnerable to seismic activity. For example, one side of a structure, usually the uphill side, may behave more rigidly due to shorter columns, while the downhill side may exhibit greater flexibility because of longer unsupported column lengths. This asymmetry can result in non-uniform story drifts and concentrated internal forces, especially when subjected to lateral seismic loads. Additionally, soft or varying soil conditions on sloped terrain can worsen these effects, leading to differential settlements, amplification of ground motions, and increased base shear.
Key Words: Sloping ground, Soil Structure Interaction (SSI), Seismic analysis, Equivalent Static Method, Response Spectrum Analysis, Seismic Zones, Slope angel variation, Storey Drift, Storey Displacement, Stiffness Irregularity, Storey Shear, Mass Irregularity, Rigid & Flexible Diaphragm, Mode Shape, Torsional Irregularity, ETABS. 1. INTRODUCTION
Besides geometric and geotechnical challenges, diaphragm behavior plays a crucial role in hillside construction. The assumption of rigid diaphragms, which is often valid for flat terrain, may not apply in irregular or staggered layouts. Flexible diaphragms can cause disproportionate load distribution among lateral force-resisting elements, further complicating the structural response.
Earthquakes are one of the most devastating natural hazards, capable of causing extensive damage to infrastructure, disrupting economies, and resulting in significant loss of life. Their unpredictable nature and the powerful forces they generate present substantial challenges for structural engineers, especially in regions with moderate to high seismic activity. As urban populations grow and available flat land becomes
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