Seismic Reliability of a Fixed Offshore Platform Against Collapse

2014 ◽  
Author(s):  
Mojtaba Dyanati ◽  
Qindan Huang
Keyword(s):  
Seismic Performance ◽  
Limit State ◽  
Shear Capacity ◽  
Offshore Platform ◽  
Ultimate Limit State ◽  
State Function ◽  
Base Shear ◽  
Offshore Structure ◽  
Seismic Reliability ◽  
Fixed Offshore Platform

As many jacket type steel platforms have been constructed in the highly active seismic area, seismic reliability evaluation of such structures is desirable. Ultimate limit state (ULS) with base shear capacity and demand can be used to estimate seismic performance of fixed offshore platform against collapse. Base shear capacity is evaluated from pushover analysis on a 3D finite element model of the offshore structure using different load patterns. Base shear demand is calculated from spectral acceleration at a given site and the total mass of the platform. Uncertainties are considered in both capacity and demand evaluations. With the limit state function, seismic fragility of a prototype structure is assessed using reliability analysis. The results indicate that various load patterns affect the seismic performance evaluation. It is also found that the steel yield stress is a critical parameter in the reliability of the steel jacket platforms.

Wave Load Prediction on a Stationary Bergy Bit Near a Fixed Offshore Platform

2017 ◽  
Author(s):  
Dong Cheol Seo ◽  
Tanvir Sayeed ◽  
M. Hasanat Zaman ◽  
Ayhan Akinturk
Keyword(s):  
Water Level ◽  
Offshore Structures ◽  
Air Gap ◽  
Offshore Platform ◽  
Load Prediction ◽  
Wave Load ◽  
Offshore Structure ◽  
Cfd Simulations ◽  
Simulation Performance ◽  
Fixed Offshore Platform

Offshore oil and gas operations conducted in harsh environments such offshore Newfoundland may pose additional risks due to collision of smaller ice pieces and bergy bits with the offshore structures, including their topsides in the case of gravity based structures particularly in extreme waves. In this paper, CFD (Computational Fluid Dynamics) prediction for wave loads acting on a bergy bit around a fixed offshore platform is presented. Often the vertical column of a gravity based structure is designed against ice collisions, if operating in such an environment. In practices, topsides are usually protected by being placed sufficiently high from the still water level, away from the reach of the bergy bits. This vertical clearance between the still water level and the topside deck is known an air gap. Hence, the amount of the air gap planned for such an offshore structure is an important factor for the safety of the topsides at a given location. In this study a CFD method is applied to estimate the dynamic response of the bergy bit and provide a reliable air gap to reduce the potential risk of the bergy bit collision. In advance of more complex collision simulations using a free-floating ice for the airgap design, CFD analysis of wave load prediction on a stationary bergy bit is carried out and reported in this paper. In the experiments and CFD simulations, the location of the bergy bit is changed to quantify the change of wave load due to the hydrodynamic interaction between the bergy bit and the platform. Finally, the results of the CFD simulations are compared with the relevant experiment results to confirm the simulation performance prior to the free floating bergy bit simulations.

SEISMIC PERFORMANCE OF SCALED IBS BLOCK COLUMN FOR STATIC NONLINEAR MONOTONIC PUSHOVER EXPERIMENTAL ANALYSIS

2017 ◽  
Vol 80 (1) ◽  
Author(s):  
Chun-Chieh Yip ◽  
Abdul Kadir Marsono ◽  
Jing-Ying Wong ◽  
Shu-Chi Lee
Keyword(s):  
Seismic Performance ◽  
Shear Capacity ◽  
Full Scale ◽  
Load Prediction ◽  
Base Shear ◽  
Scaling Factors ◽  
Scaled Model ◽  
Performance Levels ◽  
Non Linear ◽  
Block Column

This paper presents the seismic performance of the down scaled 1:5 model IBS block column with non-linear static analysis. The aim of this research is to access the ultimate capacity and structural behaviour of the IBS block column. This paper demonstrates the theoretical prediction of the full-scale prototype strength based on scaling factors at non-linear state. Besides, this research investigates the ultimate shear capacity, stiffness, bolt strength, inter-storey drift and block separation for prediction of seismic performance levels. Concrete material properties, mix specification and steel reinforcement detailing for scaled model are tabulated in this paper. The methodology of this research begins with full scale prototype design, scaling to the small model and followed by the scaled model fabrication. Theoretical lateral load prediction associated with scaling factors are also performed. The experiment test was carried out on the assembled scaled 1:5 IBS block column with proper displacement measuring equipment on test rig and graphical capture tools. The data of roof top displacement with base shear capacity, inter-storey drift and gap separations were tabulated for discussions. The tested ultimate roof top displacement was 128 mm with 3.1 kN base shear. The calculated elastic stiffness of the IBS block column was 0.137 kN/mm, followed by yielding stiffness of 0.033 kN/mm and 0.014 kN/mm plastic stiffness. The significant inter-storey drift was due to cracking and crushing of column blocks edges. The measured maximum separation gap was 24.4 mm located at 340 mm height due to the rocking of the column. Based on seismic performance levels indicator from FEMA 273 & 356, the column was in the state of immediate occupancy with 21 mm roof top displacement and 1.7 kN base shear. The life safety is limited at 65.27 mm roof top displacement with 2.4 kN of base shear. All scaled down data was then reverted to full scale prototype capacity according with the respective scaling factors. It concluded that the IBS blockwork column is capable of resisting the seismic event without falling of the blocks that endanger the occupant life at the maximum credible earthquakes of 1.3 g horizontal spectral acceleration equivalent to X+ Mercalli’s scale.

Seismic Reliability Analysis of Complex Structure

2012 ◽  
Vol 446-449 ◽  
pp. 2321-2325
Author(s):  
Zhi Yong Zhang ◽  
Wen Bo Huang ◽  
Yue Fa Zhou ◽  
Tian Shu Song
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Reliability Analysis ◽  
Structural Reliability ◽  
Limit State ◽  
Complex Structure ◽  
State Function ◽  
Limit State Function ◽  
Seismic Reliability ◽  
Element Method

The seismic reliability analysis of complex structure is carried out based on the response surface method and finite element method. Firstly, the appropriate design points are selected based on the mean values and standard deviations of the basic random variables. Secondly, the finite element method is employed to obtain the values of the limit state function of the complex structure. Thirdly, with selected design points and the obtained values of the limit state function of the complex structure, a polynomial function is constructed to approximate the original implicit limit state function. Then, with the established explicit polynomial limit state function and available methods of structural reliability analysis, the seismic reliability of the complex structure is estimated. Numerical analyses show that the established method is simple to use for the evaluation of the reliability analysis of complex structure.

Seismic Reliability Analysis Based on Characteristics of Failure Function for RC Frame Columns with Large Eccentric Compression

2011 ◽  
Vol 94-96 ◽  
pp. 1488-1493
Author(s):  
You Bao Jiang ◽  
Yu Lai Zhao ◽  
Wei Jun Yang
Keyword(s):  
Limit State ◽  
State Function ◽  
Rc Frame ◽  
Design Code ◽  
Seismic Reliability ◽  
Earthquake Loads ◽  
Failure Function ◽  
Eccentric Compression ◽  
Practical Limit ◽  
Approximate Linearization

Based on the analytical method, the failure function is obtained for reinforced concrete (RC) frame columns with large eccentric compression under vertical and horizontal loads together. A special characteristic is found that the whole correlative curve of vertical and horizontal loads may contain some rising parts under limit state, and the corresponding determinant condition is also proposed. With the approximate linearization of rising parts, the practical limit state function is also obtained. Then, the seismic reliability is calculated for RC frame columns with large eccentric compression under different combined ratios of gravity and horizontal earthquake loads according to the current Chinese design code. The results indicate that its reliability is lower than the reliability of RC frame beam when the strong column coefficient adopts low values. This provides some useful references for engineers to design RC columns with large eccentric compression reasonably.

Reliability Analysis of Marine Platforms Subject to Fatigue Damage for Risk Based Inspection Planning

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Ernesto Heredia-Zavoni ◽  
Francisco Silva-González ◽  
Roberto Montes-Iturrizaga
Keyword(s):  
Fatigue Damage ◽  
Wave Height ◽  
Limit State ◽  
Probability Of Failure ◽  
Shear Capacity ◽  
State Function ◽  
Strength Ratio ◽  
Inspection Planning ◽  
Reserve Strength ◽  
State Functions

The probability of failure of steel jacket platforms subjected to fatigue damage is computed by means of Monte Carlo simulations using limit state functions in which wave, wind, and deck loadings are expressed in terms of empirical functions of uncertain maximum wave height. Limit state functions associated with the base shear capacity of the jacket and the shear capacity of the deck legs were used. The sensitivity of the probability of failure to the coefficient of variation of resistance, of wave height, of resistance and loading biases, and to parameters in empirical loading functions, as well as the influence of the reserve strength ratio is analyzed using a simplified limit state function. Results from simulations are compared to those obtained with a formulation that relates the reserve strength ratio to the reliability index. An application to risk based inspection planning for extension of the service life of a platform is given.

Reliability Analysis of Mooring Lines of Floating Structures Under Corrosion and Material Degradation

2020 ◽  
Author(s):  
Ricardo Soares Gomes Junior ◽  
Paulo Mauricio Videiro ◽  
Paulo de Tarso Themistocles Esperança ◽  
Luis Volnei Sudati Sagrilo
Keyword(s):  
Reliability Analysis ◽  
Failure Probability ◽  
Limit State ◽  
Gas Production ◽  
Ultimate Limit State ◽  
Offshore Structure ◽  
Material Degradation ◽  
Mooring Lines ◽  
Piecewise Constant Model ◽  
Over Time

Abstract This paper presents a procedure for reliability analysis of mooring lines of floating units for oil and gas production considering corrosion and material degradation over time. The proposed procedure is limited to the ultimate limit state (ULS) and considers mooring lines made up of chain and polyester rope segments, although the same methodology can be applied to cases with steel wire segments. The proposed procedure can also be applied for mooring lines connected to any other type of floating offshore structure. For reliability assessments, it is necessary to consider the distributions and the probabilistic aspects of the random variables involved in the process. The weakest link system is used to model the strength of a mooring line segment. Simplified time-dependent probabilistic models for chain corrosion and polyester degradation are adopted to predict the strength degradation over time. The annual failure probability for different years is estimated by approximating the degraded strength by a piecewise constant model in order to perform a time variant reliability analysis. Monte Carlo simulations are used to determine the failure probability. A study case is also presented, where annual extreme top tension is obtained from long-term statistics considering Brazilian offshore environmental conditions acting on a turret moored floating, production, storage and offloading unit (FPSO).

scholarly journals Evaluating the Behaviour Factor of Medium Ductile SMRF Structures

2017 ◽  
Author(s):  
Djamal Yahmi ◽  
Taïeb Branci ◽  
Abdelhamid Bouchaïr ◽  
Eric Fournely
Keyword(s):  
Limit State ◽  
Pushover Analysis ◽  
Design Procedure ◽  
Ultimate Limit State ◽  
Eurocode 8 ◽  
Q Factor ◽  
Local Response ◽  
Base Shear ◽  
Behaviour Factor ◽  
Steel Moment Resisting Frames

In seismic codes, the capacity of structures is calculated using capacity design procedure based on the concept of base shear. The critical parameter in this procedure is the behaviour factor (q-factor), which allows designing the structures at the ultimate limit state accounting for their ductility and reserve strength. In this paper, the q-factor is evaluated for medium ductile steel moment-resisting frames (SMRF) using pushover analysis. The influence of specific parameters, such as the stories number, the “Column/Beam” capacity and the local response of structural members, is studied. The results show that the most important parameter that affects the q-factor is the local response of first-storey columns, while the “Column/Beam” capacity has a less effect on this factor. Furthermore, it is observed that the q-factor value assigned to the studied frames in Eurocode-8 is systematically underestimated for low-rise frame, while the use of this value for high-rise frame is potentially unsafe.

scholarly journals Seismic Performance of Base-Isolated Precast Concrete Shear Wall Structure with AHW Connections

2018 ◽  
Vol 2018 ◽  
pp. 1-22 ◽  
Author(s):  
Wei Wang ◽  
Aiqun Li ◽  
Xingxing Wang
Keyword(s):  
Seismic Performance ◽  
Base Isolation ◽  
Ground Motions ◽  
Precast Concrete ◽  
Shear Wall ◽  
Shaking Table ◽  
Structure Model ◽  
Base Shear ◽  
Seismic Reliability ◽  
Absolute Acceleration

To improve the seismic performance and seismic reliability of precast concrete shear wall (PCSW) structure with improved assembly horizontal wall connections (AHW connections), base isolation technology was proposed to be applied in the PCSW structure. Two 1/4-scaled structure models using the improved AHW connections were constructed: a lead-rubber bearing (LRB) base-isolated PCSW structure model and a base-fixed PCSW structure model. Shaking table tests were conducted on these two models with three strong ground motions to assess the seismic performance of the structures. It was found that the improved AHW connections in the base-isolated PCSW structure are useful and effective and that they fulfil the requirements to be met by the connections to withstand an earthquake. In addition, the maximum absolute acceleration and base shear force of the base-isolated PCSW structure model were less than those of the base-fixed PCSW structure model, and the isolation effect on the absolute acceleration responses and base shear responses increased with increase in the intensity of ground motions. In a word, the seismic performance and seismic reliability of PCSW structures can be effectively improved using base isolation technology. After this investigation, the seismic responses of the base-isolated PCSW structure model were numerically simulated using OpenSees software. There was a reasonable agreement between the numerically simulated results and test results; thus, the numerical simulation method and analysis model used for the base-isolated PCSW structure model were verified.

scholarly journals Structural Behavior of Large-Scale I-Beams with Combined Textile and CFRP Reinforcement

2020 ◽  
Vol 10 (13) ◽  
pp. 4625 ◽  
Author(s):  
Jan Bielak ◽  
Maximilian Schmidt ◽  
Josef Hegger ◽  
Frank Jesse
Keyword(s):  
Reinforced Concrete ◽  
High Performance ◽  
Large Scale ◽  
Concrete Strength ◽  
Limit State ◽  
Shear Capacity ◽  
Flexural Behavior ◽  
Ultimate Limit State ◽  
Full Potential ◽  
Line Load

With the innovative composite material carbon-reinforced concrete, thin-walled, high-performance components can be realized. A combination of carbon fiber reinforced polymer (CFRP) bars and non-metallic textile grids is advantageous as it exploits the full potential of the high-performance materials to reduce dead loads, increases durability, and extends lifespan. For new components with such mixed reinforcement, applicable design concepts and engineering rules are necessary to accurately determine the structural and deformation behavior. To validate models and detailing rules previously developed, three large carbon reinforced concrete I-beams were designed and tested to failure with a realistic line load. CFRP bars served as principal bending reinforcement, whereas shear and flange reinforcement consisted of textile grids. Results showed that existing models for bending using variation of strain distribution as well as non-linear finite-element analysis predicted the flexural behavior of structural components with mixed reinforcement in ultimate limit state (ULS) appropriately. Yet, calculation of shear capacity requires further studies to determine textile reinforcement contribution and estimate reduction for concrete strength in reinforced compression struts. For serviceability limit state (SLS), three methods for determination of deflection delivered good results. In future, a rethinking is required with regard to the ductility and robustness of CFRP-reinforced concrete components. In this respect, pronounced cracking as well as the large ultimate strain and deflection compensate for the lacking yield capacity of the reinforcement.

scholarly journals Ultimate Limit State Function and Its Fitting Method of Damaged Ship under Combined Loads

2020 ◽  
Vol 8 (2) ◽  
pp. 117 ◽  
Author(s):  
Zhiyao Zhu ◽  
Huilong Ren ◽  
Chenfeng Li ◽  
Xueqian Zhou
Keyword(s):  
Limit State ◽  
Least Square ◽  
Ultimate Limit State ◽  
State Function ◽  
Limit State Function ◽  
Combined Load ◽  
Smith Method ◽  
Fitting Method ◽  
Ultimate Limit ◽  
Damaged Ship

The ultimate limit state function is one of the premises for the assessment of structure strength and the safety of ships under severe conditions. In order to study the residual strength of damaged ships under the combined load of vertical and horizontal bending moments acting on the hull girder, the ultimate limit state function of a damaged ship under combined load, and its fitting methods are investigated in this paper. An improved Smith Method is adopted to calculate the residual load carrying capacity of damage ships, where the rotation and translation of the neutral axis of the damaged cross-section are obtained using a particle swarm optimisation method. Because the distribution curve of the residual load carrying capacity of a damaged ship under combined load is asymmetric, the application of traditional explicit polynomial fitting methods results in poor accuracy. In this study, a piecewise weighted least square fitting method is adopted so as to guarantee the continuity in the transitions, and a method is proposed for fitting the ultimate limit state function of a damaged ship under combined load. Calculations of the residual strength show that the improved Smith Method is more accurate than the original Smith Method for the accurate position of the neutral axis. The error analysis of the fitting methods shows that the ultimate limit state function that is fitted using a piecewise weight least square method is more accurate.

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