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Relative Weightage of Selected Structural Parameters on Overall Vulnerability of RC MRF BuildingsAuthor: Aniket Bhalkikar Date: 2022-03-26 Report no: IIIT/TH/2022/22 Advisor:Pradeep Kumar Ramancharla AbstractDetermination of seismic safety of existing buildings is a time consuming and challenging process. Instead, rapid visual survey methods were developed which also identify deficient structures from a large building stock in a city or town. These rapid visual screening (RVS) methods are quick and require minimal time. The important part of any RVS method is identifying critical architectural and structural features, i.e., irregularities (also known as vulnerable parameters). The score value assigned to each vulnerable parameter plays a vital role in deciding the risk of the building. Therefore, it also matters significantly that how these score values are derived. In the last two decades, several RVS methods were developed by many researchers and civil engineering professionals in India. The study in this thesis begins with a comparison and critical review of existing RVS methods used for seismic assessment of existing reinforced concrete buildings. The study focuses on rapid visual screening methods developed for the safety assessment of reinforced concrete buildings in the Indian subcontinent and a widely used method in the United States. The comparison is carried out in various ways. Initially, a direct comparison is made based on vulnerable parameters and damage grades proposed by each method. Later, a scoring system is developed to highlight the differences and rank the selected methods. It was observed that there are many uncommon vulnerable parameters amongst each selected method. Later, to understand the workability of each selected RVS method, a rapid visual survey was conducted on 100 reinforced concrete buildings in three different cities (viz., Pithoragarh, Gangtok, and Agartala) in India. The results of all five methods were found to have different outputs with significant variation for the same sample of surveyed buildings in each city. From investigation on such varying results, it was observed that relative weights assigned to each vulnerable parameter are different in each RVS method. Therefore, it was felt necessary to fix the relative weights of each vulnerable parameter to have unanimity in the results of different RVS methods. The present study attempts to derive the relative weights of the few selected vulnerability parameters on overall vulnerability of reinforced concrete moment resisting framed buildings using a numerical approach. To determine the relative weight of any vulnerable parameter, it is necessary to understand and effectively quantify its effect on the global response of the building. The quantification of the impact can be determined with the use of an appropriate damage index. The study presents a brief discussion of currently available and widely used damage indices along with their pros and cons. From the literature study on damage indices, the most suitable index with some modifications is adopted in this study. As a modification, the study proposes the hinge state coefficients and the procedure to derive the same. Thus, the vulnerability index can be determined using these hinge state coefficients and the total number of hinges formed in a structure. To derive the relative weights, the inelastic performance of irregular frames is compared with the performance of regular frames. The irregularities (i.e., vulnerable parameters) considered in this study are old building (i.e., building designed with previous code), open ground storey, floating column, and the taller floor. Nonlinear static analysis is performed on all regular as well as irregular frames to study the inelastic behaviour. The regular frames and irregular frames are initially compared based on the results of nonlinear static analysis and later based on calculated vulnerability index values. The vulnerability index values are determined at the global level and storey level as well. The comparison based on capacity curves and hinge patterns show a drastic change in irregular frames. Finally, a statistical analysis of the thypothesis test on data sets of regular and irregular frames was used to estimate the relative weights of selected vulnerability parameters. The results show that the floating column vulnerable parameter has the worst effect on global damage of structure for infill frames, followed by the open ground storey, building designed with previous code, and taller floor. Full thesis: pdf Centre for Earthquake Engineering |
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