الفهرس 
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Abstract
Quite number of oil platforms located on the Red and Mediterranean Sea in Egypt wasinstalled in 1961. Despite their aging status, some of these platforms continue to producean economically viable amount of oil and gas. In order to ensure the platforms areoperationally safe during life time, an existing offshore structure shall undergo anassessment to demonstrate its fitness for purpose if a major alter from design phase orextension of lifetime is occur.Structural assessment is a key part of the structural integrity management(SIM) processfor ensuring the fitness-for-purpose of offshore fixed platforms. Structural IntegrityManagement (SIM) is important for the protection of offshore crew, environment,business assets and company and industry reputation. The thesis outlines procedures inplace for reassessment, including those in the different code and standards. The methodsnormally used for assessment of existing offshore structures are based on design levelcheck, ultimate strength check or on a probabilistic approach. This thesis representprocedure to undergo the assessment of structure using the design level check. In-service,Spectral Fatigue and Simplified Fatigue Analysis are conducted to check that thestructure is fit for purpose and to cover the requirement of code and standard for designassessment method.In-service Static Analysis carried out to ensure that the structural member withall appurtenances is capable of supporting the applied loads in both storm (100 years) andoperating (1 year) conditions. A static analysis calculates the effects of steady loadingcondition on a structure, while ignoring inertia and damping effects such as those causedby time-varying loads. Static analysis determines the displacements, stress, strains andforces in structures caused by loads. The Structural Analysis was static linear analysis ofthe structure above the seabed combined with static non-linear analysis of the interactionof the pile with the soil.Offshore jacket structure subject to repetitive environmental loading which is varying inmagnitude and/or direction. The fluctuation of stress and strain caused by the timevarying loading may lead to its failure at stress much lower than the static strength. Theobject of the fatigue analysis is to ensure that all tubular connection under cyclic stresscondition have lives in excess of the design life of the platform. this thesis represents theprinciple of different fatigue analysis method. A fatigue analysis of offshore structurescan in general terms be described as a calculation procedure, starting with theenvironment (waves) creating stress ranges at the hot-spot regions and ending with thefatigue damage estimation. The link between the waves and the fatigue damage estimateis formed by mathematical models for the wave forces, the structural behaviour and thematerial behaviour. Spectral fatigue analysis is the most comprehensive of fatigueanalysis procedures and is the one which best represents the random nature of the waveenvironment. The determination of cyclic loading conditions has been carried out bymeans of a stochastic wave approach, while the stress response for each sea state hasbeen determined with the spectral analysis technique.Structural Reliability treats uncertainties in structural design systematically, evaluatingthe levels of safety and serviceability of structures. In order to ensure the structural safetyduring the service life of a structure, maintenance and risk mitigation are required.Fatigue deteriorating phenomenon is a major failure mode accounted for explicitly indesign codes of offshore structures in order to assure structural safety along the servicelife. Reliability is the entity that will compromise the two requirements of design;structural integrity and economy. Over the last decade reliability-based methods havebeen increasingly utilized in the offshore industry as an efficient tool for optimizingunderwater inspection and maintenance in view of fatigue cracks. the thesis covers a briefoverview of reliability analysis and describe the procedure followed and the method usedfor computation of the fatigue reliability analysis of the jacket welded structuralconnections of the platform in installed condition. Based on result of fatigue analysis andbased on the simplified fatigue reliability method described in this thesis an evaluation ofreliability index has been conducted to assure the safety of the structure.