SEISMIC BEHAVIOUR OF THE IRREGULAR RC STRUCTURE SUBJECTED TO SINGLE AND MULTIPLE EARTHQUAKE EXCITATIONS

Abstract

Urban infrastructure often comprises buildings with irregular designs, influenced by occupational and architectural requirements. Irregularities can be observed in various aspects of a building, such as its floor plan, elevation, distribution of vertical elements, and allocation of mass across different levels. Finding perfectly regular buildings in reality is rare, making them more theoretical than practical. However, these irregularities can pose a significant risk during seismic activity, as they can amplify displacement and concentrate stresses within the structural components, potentially leading to severe damage and even collapse. One type of irregularity is vertical irregularity, which refers to variations in mass, stiffness, strength, or geometry along the height of a building. Another kind is rotational or in-plan irregularity, that develops whenever the centre of masses and rigidity are not aligned along a similar vertical direction at each floor level. When lateral forces or earthquakes occur, the resistive force operates along the centre of stiffness, whereas the force of inertia acts along the centre of mass. The operation of the structure is torsional if it possesses in-plan eccentricity. This research aims to investigate the effects of repeated seismic waves on irregular RC buildings commonly found in urban infrastructure. Specifically, he main objective of the study is to assess the effects of mass and stiffness anomalies along the height of the building along with torsional irregularities in the structure's plans. To analyse these effects, nonlinear time history analysis is conducted using the software ETABS 20, comparing torsional responses under various scenarios. The analysis reveals that irregularities arising from differing shear wall positions exhibit more pronounced torsional irregularities compared to mass and stiffness irregularities, especially when subjected to single strong earthquakes or repeated earthquakes. The results demonstrate that double event earthquakes result in greater torsional irregularity compared to single events and triple events, while a triple event of moderate earthquakes yields similar results to a single event of a strong earthquake. This study provides valuable insights into the torsional behaviour of irregular reinforced concrete buildings when exposed to repeated earthquakes. Overall, the results highlight the critical importance of shear wall placements to assessing the torsional behaviour of such buildings, emphasising the need to take them into account when designing earthquake-resistant structures. The evaluation of different techniques involves comparing methods such as column resizing and iv reorientation, implementing Lead rubber base isolation systems to isolate a building's foundation from vibrations and seismic activity, and incorporating friction viscous dampers to minimize torsional impact during single and repeated earthquake excitations in the most vulnerable scenarios. The results clearly demonstrate the high effectiveness of these techniques in reducing torsional irregularity in structures. Notably, the incorporation of friction viscous dampers proves to be the most advantageous, resulting in the lowest displacement and minimal torsional irregularity compared to the other two techniques.