کاهش پراکندگی پاسخ لرزه ای سکو های ثابت فلزی دور از ساحل در برابر حرکات زمین حوزه نزدیک دارای پالس سرعت

Steel offshore platforms are some of those structures which are built to withstand environmental and accidental loads during oil exploitation operation. Particular attention is being paid to earthquake loads in seismic active areas because it directly influences the capacity of the offshore structure installations. The uncertainties available in earthquake loads as well as in strength of structural components and also the need to gain confidence about the performance of the structure, have convinced the engineers to use probabilistic methods for design purposes. To this end, Probabilistic Seismic Demand Analysis (PSDA) is used to compute the mean annual frequency of exceeding a particular structural response parameter. In this paper, the efficiency of advanced scalar ground motion intensity measures (IM), Inelastic Spectral Displacement (Sdi) which, was proposed by Thosong and Cornell (2007) in Stanford University, has been compared for PSDA of Jacket Type Offshore Platforms (JTOP) with conventional scalar intensity measure, Elastic Spectral Acceleration or correspondingly Elastic Spectral Displacement (Sde). An efficient Im is the one which, leads to lower dispersion in response parameter of structure in an arbitrary level of Im. In this paper, the numerical model of a Jacket Type Offshore Platform in accordance with its real behavior was simulated in OpenSees software. The case study platform has been modeled in OpenSees considering buckling and post buckling behavior of bracing members and material low cycle fatigue effects. In order to consider soil-pile-structure interaction effects, the near field soil was modeled using Beam on Nonlinear Winkler Foundation method including Lateral resistance, skin friction resistance and end bearing resistance. In the current research, Incremental Dynamic Analysis (IDA), which is among one of the most recent and capable approaches in evaluating ultimate capacity of structures, has been performed and a brief discussion has been presented about the efficiency of different Edps in indicating various structural response modes of platform. As a consequence, the same Edp as simple building structures – maximum interstory drift angle – has been proposed for case study platform. Furthermore, the multiple Ida curves in terms of two aforementioned Intensity Measures for 40 pulse-like near fault ground motion records have been depicted and the dispersion of Ida curves in dynamic instability range have been computed for these two Ims. Based on lower computed dispersion for inelastic spectral displacement intensity measure, this Im has been chosen as the most efficient intensity measure for case study platform.