This paper presents a comprehensive comparison of API and ISO seismic design requirements for off... more This paper presents a comprehensive comparison of API and ISO seismic design requirements for offshore structures. The selected critical API and ISO seismic requirements, which have significant impact on the structural design of the offshore platform, includes the simplified design response acceleration spectrum, the detailed probabilistic seismic hazard analysis, the uniform seismic hazard response spectrum, the tubular member strength and stability requirements, and the tubular joint strength requirements. An existing platform had been selected to illustrate the stress ratio comparison of the platform per WSD and LRFD design approaches.
International Journal of Offshore and Polar Engineering, 2013
This paper introduces a spectrum estimation method, called the Thomson spectrum estimation method... more This paper introduces a spectrum estimation method, called the Thomson spectrum estimation method, to effectively identify the structural system and the period of an offshore platform based on recorded topsides acceleration time histories. This method uses several leakage-resistant orthogonal windows, and the centered discrete-time Fourier transforms of these orthogonal windows appear in the solution of a particular form of a prolate spheroidal differential equation of the first order. The performance of the deepwater platform in the Gulf of Mexico under major hurricane conditions (i.e., Hurricanes Ivan, Katrina, Rita, and Ike) in terms of estimated displacement trajectories and recorded accelerations of the topsides is also investigated and presented.
This paper presents important issues that have always existed in the assessment of Arctic environ... more This paper presents important issues that have always existed in the assessment of Arctic environmental actions on exploration drilling structures and the many additional factors that must be addressed for year round production systems. Recent high level Arctic development activities have demonstrated the urgent need for better understanding of the ice strengthening, winterization, and ice management design and operational requirements for the various Arctic regions. Recent international and national Arctic rule development will be critically reviewed and the differences between the recent ISO DIS19906, API RP 2N, IACS, and DNV class requirements will be discussed. The concepts currently proposed for ship shaped, monoand multi-pod, mono-cone, caisson, and spar, drilling and production platforms and LNG terminals will be reviewed. In addition the design philosophy for stiffened plates or shells of revolution that form the basic common load resisting component will be evaluated under ...
Dynamic Response of the Baldpate Compliant Tower Platform to Major Hurricanes in Gulf of Mexico
All Days, 2012
The first free-standing compliant tower structure, Hess Corporation's"Baldpate" pla... more The first free-standing compliant tower structure, Hess Corporation's"Baldpate" platform in Garden Banks Block 260 in the Gulf of Mexico, wasinstalled in a water depth of 1,648 ft in 1998. After its installation, Hessinstalled accelerometers at the upper deck level. Since then, four majorhurricanes have occurred in the Gulf of Mexico: Ivan (2004), Katrina (2005), Rita (2005), and Ike (2008). The platform has been analyzed using hindcasts for several of these storms. Thework for Rita is complete and of some interest, and so it is presented in thispaper. Rita was one of the most intense Atlantic hurricanes ever observed inGulf of Mexico, and its track passed just west of GB260. This paper compares, and shows good correlation between measured and predicted structural responsesfor Rita. In addition, the paper presents analysis results in terms of AISCstress ratios and pile-load safety factors. Also presented is a comparison between: the original design storm criteria;newly...
An explicit closed-form solution for linear systems subjected to nonstationary random excitation
Probabilistic Engineering Mechanics, 1996
Explicit, closed-form solutions are presented for the correlation matrix and evolutionary power s... more Explicit, closed-form solutions are presented for the correlation matrix and evolutionary power spectral density matrix of the response of a linear, classically damped MDOF system subjected to a uniformly modulated random process with the gamma envelope function. The effects of the statistical cross-modal correlations on the evolutionary mean square responses are investigated. A simple MDOF system subjected to ground motion
This paper presents the rigorous methodology and structural analysis procedures required for nonl... more This paper presents the rigorous methodology and structural analysis procedures required for nonlinear dynamic soil-pile-structure-interaction analysis of offshore platforms under ductility level earthquakes with emphasis on the soil liquefaction conditions. The nonlinear inelastic soil properties including the cyclic strain rate, gapping, and the hysteretic energy dissipation are considered. The non-linear beam-column element and non-linear strut element, which were calibrated with numerous test results for offshore structures, are modeled and presented. Three sets of representative ground motion time histories, which characterize the likely envelop of ground intensity, frequency content, phasing and duration expected at the site, are considered in the analysis. The comparison of the evolutionary power spectral density of the earthquake ground motion accelerations is outlined for soil liquefaction and non-liquefaction conditions in terms of the intensity and frequency content of the ground motion accelerations. The impact of the soil liquefaction conditions on the structural response and especially for the pile foundation system design, are illustrated using a recently successfully designed platform in the seismic active area offshore Trinidad. API and ISO seismic design requirements are briefly discussed. The most critical structural components of the pile-jacket connections design are demonstrated by the nonlinear finite element analysis with the large deformation of the platform and the material plasticity of the steel considered.
Fully Nonstationary Analytical Earthquake Ground-Motion Model
Journal of Engineering Mechanics, 1997
... stationary, BXt is infinite. If BXf is finite, the nonstationary pro-cess Xk(t) is termed sem... more ... stationary, BXt is infinite. If BXf is finite, the nonstationary pro-cess Xk(t) is termed semi-stationary. The characteristic width ... process St(i), respectively. The stationary Gaussian pro-cess St(t) possesses a physical interpretation. It can be ...
Earthquake Engineering & Structural Dynamics, 1997
A recently developed earthquake ground motion model non-stationary in both intensity and frequenc... more A recently developed earthquake ground motion model non-stationary in both intensity and frequency content is validated at the inelastic Single-Degree-Of-Freedom (SDOF) structural response level. For the purpose of this study, the earthquake model is calibrated for two actual earthquake records. The objective of a constant (or target) displacement ductility used in conventional earthquake-resistant design is examined from the statistical viewpoint using this nonstationary earthquake model. The non-linear hysteretic structural behaviour is modelled using several idealized hysteretic SDOF structural models. Ensemble-average inelastic response spectra corresponding to various inelastic SDOF response (or damage) parameters and conditioned on a constant displacement ductility response are derived from the two identified stochastic ground motion models. The effects of the type of hysteretic behaviour, the structural parameters, the target displacement ductility factor, and the ground motion model on the statistics of the inelastic response parameters are thoroughly investigated. The results of this parametric study shed further light on the proper interpretation and use of inelastic response or damage parameters in earthquake-resistant design in order to achieve the desirable objective of 'constant-damage design'.
Proceedings, 13th World Conference on Earthquake Engineering, Vancouver, British Columbia, Canada, Aug 1, 2004
SUMMARY New explicit closed-form solutions are derived for the mean upcrossing rate of nonstation... more SUMMARY New explicit closed-form solutions are derived for the mean upcrossing rate of nonstationary response quantities of linear elastic, both classically and non-classically damped, multi-degree-of-freedom (MDOF) systems subjected to a fully nonstationary earthquake ground motion process. The stochastic earthquake ground motion model used in this study captures the temporal variation of both the amplitude and frequency content typical of real earthquake ground motions. The analytical results obtained are applied to ...
This paper details two fatigue analysis approaches, that is, time history and spectral fatigue an... more This paper details two fatigue analysis approaches, that is, time history and spectral fatigue analyses for truss spar under in-place and transocean dry tow environmental conditions. For the efficiency of in-place time history fatigue damage calculation, a method to condense the seastates is introduced based on a closed form solution of the fatigue damage calculation. The typical fatigue hot-spot locations of the deepwater Truss-Spar are identified. The barge structural flexibility effect on the tow fatigue analysis results is summarized. A real TrussSpar platform successfully installed and operated in the Gulf of Mexico (GOM) more than 10 years with water depth greater than 3000 feet is presented. Since this deep-water platform had successfully withstood the major hurricanes (e.g., Ivan, Katrina, Rita, and Ike) and is still operating subjected to under-water inspections as per the requirements of BSEE, it had been proved that the original fatigue analysis approaches are practically...
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