Aniket Nitin Bhalkikar received his doctorate in Civil Engineering (CE). His research work was supervised by Prof. Pradeep Kumar Ramancharla. Here’s a summary of his research work on Relative Weightage of Different Vulnerable Parameters on Overall Vulnerability of Structure:
Determination 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 requires minimal time. The important part in any RVS method is the identification of critical architectural and structural features i.e., irregularities (also known as vulnerable parameters). The score value assigned to each vulnerable parameter plays an important role in deciding the risk of the building. Therefore, it also matters greatly that how these score values are derived. In 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 vulnerability 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 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 is 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 using numerical approach.
To determine the relative weight of any vulnerable parameter, it is necessary to understand and effectively quantify its effect on global response of building. The quantification of effects can be determined with the use of appropriate damage index. The study presents the 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 modification, the study proposes the hinge state coefficients as well as the procedure to derive the same. Thus, the vulnerability index can be determined using these hinge state coefficients and 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 frame. The irregularities (i.e., vulnerable parameters) considered in this study are pre-code gravity designed building, 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 results of nonlinear static analysis and later based on calculated vulnerability index values. The vulnerability index values are determined at global level and at storey level as well. The comparison based on capacity curves and hinge pattern show a drastic change in the results of irregular frames. Finally, a statistical analysis of t-hypothesis test on data sets of regular and irregular frames was used to estimate the relative weights of selected vulnerable parameters. The results show that for infill frames, floating column vulnerable parameter has worst effect on global damage of structure followed by open ground storey, pre-code gravity design and finally taller floor.