Study of RC Frame Structures with Plan Irregularities using Response Spectrum Method

Abstract

One of the main causes of seismic damage amplification is structural irregularities. Indeed, past earthquakes have shown that structures with irregular configuration or asymmetric distribution of structural characteristics are subject to increased demand for seismic damage. The sources of irregularityin a construction setup can be multiple and of distinct types and are generally categorized into two main classifications: plan and elevation irregularities. Both these types of irregularitiesofteninvolvethedevelopmentoffragilecollapsemechanismsowingtoalocalrise in seismic demand in particular components that are not always sufficientlysupplied with structure. Among the two kinds of structural irregularities mentioned above, in-planirregularities appear to have the most adverse effects on the applicability of classical nonlinear static processes (NSPs), exactly because such techniques have been created for the seismic evaluation of buildings whosebehavior is mainlytranslational. This is whyexperts in this sector have extensively researched the expansion of NSPs to plan uneven construction structures in latest years. This dissertation is therefore aimed at studying and understanding the critical behavior of irregularity in plans constructions subject to seismic excitement. The main parameters for determining the performance point of all 10 designs, modelled in Etab 9.6.2,were lateral displacement, storey drift, base shear, storey displacement. The findings of all 10 modelsareprovidedfromsoftwareconsistingofResponseSpectrumcurveandhingeformation, which generates consciousness of planning easyscheduled constructions to minimizethe impact of theearthquake.

Introduction

The lateral force resisting system (L.F.R.S) in buildings resists seismic forces and typically includes special moment-resistant frames, shear walls, and dual systems. Structural damage during earthquakes often begins at weak points caused by irregularities in stiffness, strength, and mass distribution, which can be categorized as plan or vertical irregularities.

This study focuses on seismic analysis of 15-story reinforced concrete regular and irregular buildings using IS 1893-2002 (part 1).

The dissertation is organized into six chapters covering introduction, literature review, structural modeling, analysis methodology (ETABS software), results discussion, and conclusions with future scope.

Literature Review Highlights:

• Plan Irregularities: Uneven mass, stiffness, and strength distributions in building plans are major contributors to seismic damage. Research spans from simple single-story models to complex multi-story models, though single-story models remain common due to simplicity.

• Eccentricity Types: Studies classify eccentricities causing torsional effects into mass eccentricity, stiffness eccentricity, and strength eccentricity, influencing seismic responses differently.

• Key Research Findings:

  • Early studies by Tso, Sadek, and others analyzed torsional and inelastic seismic responses.

  • Code provisions for seismic design (NEHRP, ATC, NBCC, EC8) vary in effectiveness depending on building eccentricity and stiffness.

  • Torsional coupling and imbalance affect ductility demands and deformation patterns.

  • Interaction between axial and horizontal forces reduces floor rotation by about 20%.

  • Balanced positioning of strength and stiffness centers (CV and CR) reduces torsional effects and improves seismic performance.

  • Near-fault and far-fault ground motions impact stiff and flexible edges differently in asymmetric buildings.

• Modeling Approaches: Researchers use elastic and inelastic analysis, hysteresis models, and modal analysis to study the seismic response of asymmetric and irregular structures.

• Design Implications: Adjustments in design eccentricity and strength distribution improve structural performance under seismic loads, emphasizing the importance of understanding irregularities in building plans.

Conclusion

The building component resisting seismic forces is known as the lateral force resisting system (L.F.R.S). The building\'s L.F.R.S may be of different types. The most common forms ofthese systems in a structure are special moment-resistant frames, shear walls and dualframe-shear wallsystems. The damage ina structure generallystarts atthe location of the weak structural planes present in the building systems.

Copyright

Copyright © 2025 Vishal Yadav, Abhishek Rana. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.