الفهرس 
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Abstract
In terms of the importance of offshore structures in the oil production, in Egypt, this research was initiated with the objective of investigating their fatigue in order to propose a measure to extend their lifetime and increase their resilience. The research was conducted in the Structural Engineering Department, faculty of Engineering, Alexandria University (Egypt). Primarily, the problem was defined and objectives were set to which a methodology was designed. It encompassed 4 investigation phases (Le. theoretical, modelling, analytical and inferential phases). During Theoretical Phase, literature was reviewed in the field of partially grouted tubular members that increased the fatigue resistance of offshore underwater tubular members. Through Numerical Modeling Phase, a finite element analysis was conducted for 6 tripod models 10, 15 and 20 m high with grouted tripod legs. Tripods models were subjected to one time to variable vertical loads and second time to variable horizontal loads in order to investigate the strengthening mechanism and study its impacts. Moreover, many parametric studies on offshore substructures with variable geometrical properties, grout strength and fatigue load effect are carried out to study the effect of grouting on fatigue resistance and strengthening of main members. Throughout Analytical Phase, the results were compared to previous data to calibrate finite element models for further parametric study. During the course of Inferential Phase, conclusions were deduced to indicate that such structures could, be upgraded to carry new loads thus (extending its lifetime. In addition, design recommendations were suggested regarding the in-grouted tubular T and Xjoints. The results indicated a significantly high value of filled grout for increasing fatigue life, increase their strength of model to carry more loads and reducing the alternative equivalent stresses in legs of models. Moreover the strengthen and fatigue repair process will lead to increased the life time of platforms for many years instead to construct a new platform which is happened Nowadays.