Sharif Digital Repository

Nowadays, according to existence of oil resources in offshore areas and the necessity of extracting, constructing of offshore platforms is developed. The design of these structures has high effect on the cost of construction and maintenance and the performance under the loads such as wave, earthquake, impact, etc. Therefore, if the analysis of platform structure is more accurate the evaluation of the behavior and consequently the better design in different conditions is better. In this thesis, a modification of Endurance Wave Analysis (EWA) in evaluation of offshore structures is introduced in this study. EWA is a new method to predict the response of offshore structures in different sea... 

Marine structures are always exposed to environmental loadings such as wind, wave, earthquake and sea currents. The wave-induced force could cause the critical stress in elements and due to fatigue failure, because of being random and periodical. In generally, it can be shown that fatigue is an extremely important phenomenon and one of the main problems in the long time destruction of the structure, because of severe corrosion and random loading in the marine environment.In order to reduce the effect of environmental loads, using control mechanisms is a new method to control vibrations of structures. These systems cause the reduction of structure responding such as acceleration, velocity and... 

A structural system will normally fail as a result of a chain of failures of different components. In this thesis, fatigue reliability of fixed offshore platforms is investigated through analyzing different failure scenarios. In order to evaluate the occurrence probability of a special scenario, each failure scenario is divided into a finite number of sub-scenarios. To do this, all combinations of time sequences are generated for a given sequence of failures, using a specially developed program.
In order to calculate the occurrence probability of each scenario, a massive reliability analysis should be done for each of corresponding sub-scenarios. Knowing that there are a large number of... 

This thesis encompasses a number of issues in earthquake engineering which may appear quite diverse in nature. Several methodological aspects of both conventional and novel approaches to probabilistic seismic hazard assessment are discussed here along with subjects more strictly pertinent to structural and geotechnical engineering. This work, however, has a unique, ultimate goal: to provide procedures for an effective and practical probabilistic estimation of structural demand of offshore platforms due to seismic ground shaking. In modern multi-level design and rehabilitation procedures, structural performance is in fact quantified by deformation demand levels exceeded with a specified... 

Offshore platforms are one of the most important structures in oil-rich countries, so that their economic benefit makes it very expensive to stop their usage. Therefore, it is essential that their performance is not disrupted by earthquake or the tidal waves made by severe storms. According to statistics many of the offshore platforms of their design life pass and need an important loss inspection. The assessment of existing platforms is a relatively new process. The lack of comprehensive standard creates some difficulty in establishing performance requirements, on a case by case basis depending upon the risks associated with the future operations of the platform. In this study the criteria... 

Structures face various loadings and confront different circumstances as they are built and used. This situation causes the aging structures to deteriorate, which would lead to a decrease in reliability and safety. In the recent decades, the need for systems to assure the integrity of structures in terms of their age, usage and level of safety when experiencing infrequent and extreme forces such as earthquakes, tornados, hurricanes, large waves has deeply been recognized. These systems are often referred to as structural health monitoring (SHM) in the literature. The main objective of such system is to increase reliable operating lifetime. In the case of offshore structures, utilizing...