Abstract
The pile foundation nonlinearity and its influence on the ultimate capacity of fixed platforms have not comprehensively been covered by previous researchers. In this study, the seismic behavior and capacity of a newly designed and installed Jacket Type Offshore Platform (JTOP) located in the Persian Gulf is investigated by conducting Incremental Dynamic Analysis (IDA) using a suit of near-fault ground motions. Additionally, two modified models of the original platform are created by slightly increasing the diameter of the pile foundation and also softening the jacket part for evaluating the importance of the pile foundation and seismic soil-pile structure interaction on the dynamic characteristics of the JTOPs. Valuable discussions are provided to explore various aspects of the dynamic behavior of JTOPs by presenting individual and multirecords IDA curves using effective Engineering Demand Parameters (EDPs). Comparing the results of the three platform collapse fragility curves, it is concluded that the pile foundation plays a very important role in the dynamic response of offshore platforms and can drastically alter the ultimate strength of the platform together with its collapse capacity. It is observed that the proportional distribution of nonlinear behavior in the pile foundation and jacket part is the key factor in the enhancement of the ultimate strength of JTOPs. On the basis of the results derived from this paper, it is recommended that some basic requirements should be developed in order to ensure that the coupling ductility of pile foundation and jacket part is optimized during the design process. Furthermore, according to the findings from this study, some practice recommendations are presented to be devised within the design step.
Highlights
Among all lateral loadings acting on the pile supported structures, in seismically active areas, these structures may be subjected to strong ground motions where the behavior of pile foundations under lateral seismic loads becomes an important factor in efficiently assessing the performance of such structures
Strong ground motions have been a major cause of past damage in pile foundations and reliably evaluating the dynamic response of pile foundations against this type of lateral loading plays a paramount role in Jacket Type Offshore Platform (JTOP) design procedure
The ultimate strength, hysteretic response of tubular members, and cyclic inelastic behavior of jacket frames of JTOPs ignoring pile foundation part were investigated in the works of Zayas et al [6], Kayvani and Barzegar [2], Mortazavi and Bea [3], Honarvar et al [7], and Golafshani et al [8] using experimental results of frames
Summary
Among all lateral loadings acting on the pile supported structures, in seismically active areas, these structures may be subjected to strong ground motions where the behavior of pile foundations under lateral seismic loads becomes an important factor in efficiently assessing the performance of such structures. Two modified models of the original platform are created by slightly increasing the diameter of the pile foundation and softening the jacket part for evaluating the importance of pile foundation and seismic soil-pile structure interaction in the dynamic characteristics of the JTOPs. Some individual and multirecords IDA curves in terms of maximum storeylike drift ratio per unit length of pile and maximum interstorey drift ratio of jacket bracing storeys are provided and valuable discussions are presented to explore various aspects of the dynamic behavior of JTOPs. Based on the findings from this study, some practice recommendations are presented to be devised within the design step. By presenting collapse fragility curves for all three models, the effects of the pile foundation and, the proportionality of the stiffness and strength of the pile foundation and jacket part of the platform on the ultimate collapse probability of considered platforms are investigated
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