PERFORMANCE BASED DESIGN METHODOGIES USED IN GEOTECHNICAL ANALYSES
Project no. 706 · Status: Kapanmış · 2015
Summary
Many new and important projects are realizing every day in city centers. These projects are challenging engineering designs and encourages the engineering community to new design concepts. As the majority of our country lies in the high seismicity zones, seismic analysis of these important structures becomes an important research subject and needs more attention. Seismic design of structures compose of determination of the seismic environment, as well as the soil and structural properties. As can be called the fault-soil-structure interaction analysis, this procedure involves high levels of uncertainty in every step of the design starting from the possible seismic earthquake effects. Therefore, to be able to handle the uncertainty and random nature of the properties, and to give the results with an easy-to-use charts and tables, probabilistic design systematics are preferred other than the traditional deterministic analysis. One of the important objective of an engineering service is to give the results of the analysis as an appropriate and comprehensible way for not only the designer himself, but also to the project owner, a bank analyst and other important actors in the project. Therefore, the damage recurrence relationships and probability of exceedance of a given damage level shall be one of the important outputs of an engineering design. In the light of these informations, the project owner has every right to choose the design level of his project, and the designer shall therefore conclude his design based on the chosen target design levels. Therefore, first aim of this study is to give the easy-to-understand and use solution charts and graphs which determine the damage levels of the engineering problem at hand. Current design methodologies rely on the capacity based / force based design methodologies. Uncertainties and randomness throughout the design are taken into account using the somewhat rude different factor of safety values. The developments with the technology level and the scientific knowledge starts to change the design methodologies from force/based design to the displacement/based design. This new framework contains the probabilistic literature and methods and implicitly takes into account the uncertainties and random nature of the properties. This so called performance based design is used in some structural engineering problems but the use in geotechnical engineering practice is scarce. For example, in high rise buildings the performance based-design methodologies come in to be used for the displacement-control design. Actually, geotechnical engineering problems contains more uncertainties and randomness than in any other engineering branch. In the context of the study, firstly the performance based design methodologies and the study framework will be introduced. After that, two of the important problems in geotechnical engineering, namely the liquefaction phenomenon and shallow underground tunnel design will be studied based on the previously mentioned systematics. These two subjects are chosen because, they specially need important geotechnical analysis and the results of the geotechnical analysis directly influence the anticipated damage level. To be able to come up with a fragility curve, repetitive Monte-Carlo analysis will be done to get the relationship between the seismic effect and engineering design parameter. Different damage levels conforming to the engineering design parameters will be chosen from the literature studies. Earthquake time-histories will be selected from the real earthquake database, and will be scaled to different levels of intensity which will be used in the repetitive analysis. Soil properties, which will be used in the analysis, will be chosen conforming to different soil types. Finite element methods are used in the analysis. The program is chosen to be able to model the nonlinear soil properties and to be able to handle the dynamic time-domain analysis. The outcome of