Studim mbi dëmtueshmërinë e strukturave me skelet prej betoni të armuar

Abstract

This thesis describes a procedure and an example in developing the seismic fragility curves for reinforced concrete structures in Tirana. For this purpose, structures built in this city during the third decade of XX century, designed for gravity loads only, are considered. The thesis starts with a brief description of its aims and paper structure. In order to achieve its goal, different data referred to relevant institutions such as Central Technical Paper of Construction Archive; Institute of Geosciences, Energy, Water and Environment (IGEWE), many papers regarding the fragility function in international literature and numerous of studies about the vulnerability of reinforced concrete structures have been used. The thesis continues with a description of the seismic hazard in Albania as well as the entire history of the development of the design code of buildings in our country. Further, a description of the nature of the problem is given: the fragility function (curves) provide the probability of reaching or exciding a prescribed damage level for a wide range of seismic hazard. Also, a brief description of the fragility curves developed by Hazus (FEMA) in the US and those developed by Aristotle University in Thessaloniki is provided. The procedure used in this thesis is an analytical one, based on the analysis of the capacity spectrum, FraCas; which it’s theoretical basis and practical tools, were generously provided by their developers at the University College of London. First a static nonlinear analysis is carried out to obtain the capacity spectrum of the existing representative structure (the facility of Polytechnic University of Tirana). This analysis is conducted for three cases of material properties: poor quality, typical quality and good quality. Then, the damage states are defined. In this case, five damage thresholds for RC frame and dual buildings are used (Sight, Moderate, Substantial to Heavy, Very Heavy and Collapse). Secondly, a simplified SDOF model is fitted the structure’s capacity and properties for each case (poor, typical and good quality). In contrast to other capacity spectrum methods, FraCas does not rely on reduction factors or other indices to estimate the inelastic spectrum from the elastic one. Instead, it carries out, a simplified dynamic analysis on the idealized nonlinear SDOF model corresponding to the capacity curve. The conditions of local seismic hazard were considered. Because of the limited number of real time history records from the Tirana region, a set of simulated records were generated to represent the variability of seismic hazard. This way, besides the material properties variability, the natural record-to-record variability is directly considered and the resulting cloud of performance points (more than 13000 PP) is subjected to a set of regression analysis to derive the fragility function parameters (mean values and dispersion). From which, a set of fragility curve is derived. In conclusion, the results obtained in this thesis are compared with those from similar cases for RC pre-code structures in Greece. Most differences are noticed when predicting the posibility of developing slight damages, while there is almost the same prediction regarding to the probability of reaching or exciding the “collapse” damage state.