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In offshore jacket structures, the stress within the chord thickness of tubular joints arises from both membrane and bending stresses. The Degree of Bending (DoB)—the ratio of bending stress to the total stress—is key to evaluating these joints' fatigue resistance. This study delves into the DoB in tubular X-joints reinforced with fiber-reinforced polymer (FRP) subjected to in-plane bending moment. It begins by validating finite element (FE) analysis accuracy through comparison with existing theoretical and experimental evidence. Following this, the analysis of 166 joints was conducted to examine how variations in FRP characteristics (such as type, layer count, and layout) and the joints' dimensionless geometric factors influence the DoB and its ratio in reinforced joints compared to their unreinforced counterparts. Findings indicate that FRP layers enhance fatigue resistance by lowering hot spot stresses on the chord's inner and outer surfaces and elevating the DoB value by up to 26.16%. Consequently, the study introduces a parametric formula for calculating the DoB in FRP-reinforced tubular X-joints under an in-plane bending moment. This development is significant, as there was no existing parametric formula for determining DoB in FRP-reinforced joints. The proposed formula stands out for its high determination coefficient and minimal error, effectively addressing a notable gap in the field. • The Degree of Bending (DoB) evaluation in FRP-reinforced tubular X-joints under in-plane bending (IPB) is conducted. • 166 finite element models are analyzed for parametric investigation. • The influence of FRP characteristics and geometric factors on the DoB is investigated. • A parametric formula is introduced to calculate the DoB in FRP-reinforced tubular X-joints subjected to IPB moment. [ABSTRACT FROM AUTHOR]

Recent seismic events demonstrated that excessive post-earthquake residual drifts might result in high repair costs, temporary interruption of building functions due to required repairs, or even in the total destruction of the buildings. As such, minimizing residual drifts is a critical step in facilitating the rehabilitation of a building after an earthquake. To this end, a highly resilient post-tensioned self-centering yielding brace system (PT-SCYBS) has been introduced and studied. PT-SCYBS is envisioned to be implemented in new or existing diagonally braced frame systems. This system relies on the inherent self-centering behaviour of post-tensioned wires along with the yielding behaviour of the steel bars to provide a flag-shaped hysteretic response. This paper presents a comparative study of the PT-SCYBS frames, moment-resisting frames (MRFs), and buckling restrained braced frames (BRBFs) using the results from a series of nonlinear dynamic analyses. Then, a comprehensive comparative seismic performance assessment of the PT-SCYBS buildings and the reference MRF and BRBF buildings has been conducted using the FEMA P58 methodology implemented in the PACT software. The results show that the PT-SCYBSs have lower residual drifts than the reference buildings, resulting in significant reductions in the repair costs/time and casualties, and exhibit improved seismic performance. [ABSTRACT FROM AUTHOR]

In this paper, a new optimization algorithm called the search and rescue optimization algorithm (SAR) is proposed for solving single-objective continuous optimization problems. SAR is inspired by the explorations carried out by humans during search and rescue operations. The performance of SAR was evaluated on fifty-five optimization functions including a set of classic benchmark functions and a set of modern CEC 2013 benchmark functions from the literature. The obtained results were compared with twelve optimization algorithms including well-known optimization algorithms, recent variants of GA, DE, CMA-ES, and PSO, and recent metaheuristic algorithms. The Wilcoxon signed-rank test was used for some of the comparisons, and the convergence behavior of SAR was investigated. The statistical results indicated SAR is highly competitive with the compared algorithms. Also, in order to evaluate the application of SAR on real-world optimization problems, it was applied to three engineering design problems, and the results revealed that SAR is able to find more accurate solutions with fewer function evaluations in comparison with the other existing algorithms. Thus, the proposed algorithm can be considered an efficient optimization method for real-world optimization problems. [ABSTRACT FROM AUTHOR]

This paper investigates the lateral buckling of simply supported nonprismatic I-beams with axially varying materials by a novel finite element formulation. The material properties of the beam are assumed to vary continuously through the axis according to the volume fraction of the constituent materials based on an exponential or a power law. The torsion governing equilibrium equation of the simply supported beam with free warping is numerically solved by employing the power series approximation. To this end, all the mechanical properties and displacement components are expanded in terms of the power series to a known degree. Then the shape functions are obtained by representing the deformation shape of the axially functionally graded (AFG) web and/or flanges tapered thin-walled beam in a power series form. At the end, new 4 × 4 elastic and buckling stiffness matrices are exactly determined from the weak form expression of the governing equation. Three comprehensive examples each of axially nonhomogeneous and homogeneous tapered beams with doubly symmetric I-sections are presented to evaluate the effects of different parameters such as axial variation of material properties, tapering ratio and load height parameters on the lateral buckling strength of the beam. The numerical outcomes of this paper can serve as a benchmark for future studies on lateral-torsional critical loads of AFG beams with varying I-sections. [ABSTRACT FROM AUTHOR]

In this paper, a new hybrid approach is presented based on the combination of the power series expansions and the Rayleigh-Ritz method for stability and free vibration analyses of axially functionally graded non-uniform beams resting on constant Winkler-Pasternak elastic foundation. In the proposed novel technique, the power series approximation is first adopted to solve the motion equation. Regarding this numerical methodology, the transverse displacement and all mechanical properties are expanded in terms of power series of a known degree. By solving the eigenvalue problem, one can acquire the fundamental natural frequencies. According to aforementioned method, the expression of vibrational mode shape is also determined. Based on the similarities existing between the vibrational and buckling deformation shapes, Rayleigh-Ritz method is finally employed to construct eigenvalue problem for obtaining the critical loads. In order to illustrate the correctness and convergence of the method, several numerical examples of axially non-homogeneous and homogeneous beams are conducted. The obtained outcomes are compared to the results of Finite Element Analysis in terms of ANSYS software and those of other available numerical and analytical solutions. The accuracy of the method is then remarked. [ABSTRACT FROM AUTHOR]

An improved approach based on the power series expansions is proposed to exactly evaluate the static and buckling stiffness matrices for the linear stability analysis of axially functionally graded (AFG) Timoshenko beams with variable cross-section and fixed–free boundary condition. Based on the Timoshenko beam theory, the equilibrium equations are derived in the context of small displacements, considering the coupling between the transverse deflection and angle of rotation. The system of stability equations is then converted into a single homogeneous differential equation in terms of bending rotation for the cantilever, which is solved numerically with the help of the power series approximation. All the mechanical properties and displacement components are thus expanded in terms of the power series of a known degree. Afterwards, the shape functions are gained by altering the deformation shape of the AFG nonprismatic Timoshenko beam in a power series form. At the end, the elastic and buckling stiffness matrices are exactly determined by the weak form of the governing equation. The precision and competency of the present procedure in stability analysis are assessed through several numerical examples of axially nonhomogeneous and homogeneous Timoshenko beams with clamped-free ends. Comparison is also made with results obtained using ANSYS and other solutions available, which indicates the correctness of the present method. [ABSTRACT FROM AUTHOR]

Abstract The single edge notched tension (SENT) test is commonly used to evaluate the less-conservative fracture toughness of pipeline steels. The R-curve (crack tip opening displacement (CTOD)-crack growth) behavior measured by SENT tests is similar to that measured during full-scale tests. This paper compares the ductile fracture mechanism of X42 grade steel, including crack initiation and propagation, using the extended finite element method (XFEM) with experimental data obtained from SENT tests. Two major parameters in XFEM (maximum principal stress and fracture energy) were calibrated in numerical models using experimental results obtained from SENT tests performed on six X42 grade steel samples to provide a CTOD-crack growth curve. With appropriate values of maximum principal stress and fracture energy, the numerical models can reasonably reproduce the experimental results. This method could be used to anticipate full-scale test behavior and simulate crack propagation in pipelines under operational loading conditions. [ABSTRACT FROM AUTHOR]

Corrosion is identified as one of the most important deterioration factors for structural integrity of offshore platforms. For reliability analysis of these platforms, a probabilistic model for prediction of long-term corrosion loss as a function of time is essential. The purpose of this study is to propose a novel model for steel corrosion of jacket platforms in the Persian Gulf region. Field measurements for members in seawater are collected and statistically analyzed to identify the probability function for corrosion loss at different times. A new probabilistic model with time-dependent parameters is suggested, based on the statistical analysis results. Application of above-mentioned model in the reliability analysis of jacket platforms is investigated by introducing a new reliability analysis framework. This framework is a general solution for probabilistic analysis of jacket platforms with several stochastic variables which can be used for the platforms with different configuration and loads. In this framework, direct analysis is performed in each stage of first-order reliability method (FORM) instead of using the response surface method which is a common approach to obtaining the required response. This framework is applied to three jackets and the annual probability of failure (Pf) over the platforms service life is computed. Comparison of results revealed that among the years beyond the platform design life, the amount of annual Pf is increased in parabolic function. Also, studying the results is illustrated that in the case of ignoring the corrosion loss as a stochastic variable, Pf is estimated 7% lower than values obtained in actual condition. [ABSTRACT FROM AUTHOR]

A comprehensive experimental project including tension and single edge notch tension (SENT) tests was carried out on 22 inch OD X42 welded pipeline steel to determine the mechanical properties and fracture toughness of the base and weld materials. In addition to traditional clip gauge measurements, digital image correlation (DIC) methodology was applied. Crack tip opening displacement (CTOD)-crack growth and crack mouth opening displacement (CMOD)-force curves were generated for SENT specimens subjected to monotonic tension loading using a multiple specimen technique. Significant differences were observed in the behavior of base metal and weld specimens. The evidence of fracture resistance measured from the weld metal specimens being lower than that from base metal specimens is important with respect to avoiding overestimation of R-curves in integrity assessment procedures. Additionally, the weld metal tolerated more force when the CMOD was less than 0.9 mm but the base metal tolerated more force after this point, while both CMOD-force curves reached a similar value of maximum force. [ABSTRACT FROM AUTHOR]

Lattice transmission towers are critical components of power infrastructures. Collapse of a transmission tower may cause major economic and social impacts. The present study aims to evaluate the progressive collapse vulnerability of a lattice tower in a 400 kV power transmission line. The load increase factors (IF) after an instantaneous element removal are determined for application in static analyses and for design purpose. The capacity-to-demand ratios (C/D) are proposed to identify critical members after different removal scenarios. This proposed parameter is examined by comparison with Overload Factor (OF) from pushdown analysis. In addition, the pushdown analysis is used to determine the remaining capacity of the structure after removing an element. It is found that tower may resist progressive collapse because of the possible alternative load paths. It is also observed that the studied structure has less susceptibility to progressive collapse in scenarios of element removal at higher elevations. [ABSTRACT FROM AUTHOR]

Prediction of structural response to seismic loads is a complex problem with many parameters involved that some of them can behave highly uncertain. Nonetheless, it is needed to have a clear understanding of how these uncertainties affect seismic structural performance. In this matter, it is convenient to separate uncertainties into two categories: aleatory (due to variability of strong ground motions) and epistemic (related to numerical model of structure). This paper aims to investigate effects of structural uncertainties on seismic performance of steel moment resisting frames, through extended IDA of two sample 5-story frames. In this regard, damping, mass, yield strength and ultimate strength of structural steel have been considered as probabilistic variables. Latin Hypercube Sampling (LHS) has been used to create random realizations of structures. With the aid of reliability methods, different sources of uncertainty and their ranges of influence on seismic performance have been disaggregated. Two steel moment frames, despite having the same geometry, have been designed with different levels of ductility. This can give an idea about how the ductility of structure affects different aspects of probabilistic performance evaluations. Considering the results, it can be seen that uncertainties in selected parameters have important effects on seismic performance. In other words, capacity and demand estimations based only on deterministic procedures may ignore some substantial points. Including these uncertainties in performance calculations can considerably change, at some levels, the probability of achieving desired performance. Also, a clear superiority in performance capacities can be seen for special moment frame. [ABSTRACT FROM AUTHOR]

Steel jacket type offshore platforms are highly susceptible to damage because of the severe environmental condition, therefore ensuring its proper performance and detection of probable damage is very important and undeniable. In this paper, by studying on experimental results of a prototype scaled offshore platform subjected to dynamic loading for different damage conditions, efficiency of Rate of Signal Energy using Wavelet Packet Transform for damage detection of this kind of structures has been carried out. Experiments results of two support conditions including hinge based and pile supported cases have been used. Wavelet packet analysis was used to determine the location of damage for different damage scenarios. The results demonstrate that proposed method can predict location of damage accurately. It can be concluded that this method can be used for prediction of damages similar to damages considered in this paper by using a continuous measurements and monitoring of platform responses. [ABSTRACT FROM AUTHOR]

In tubular joints of offshore platforms, joints may exhibit considerable flexibility since the materials in the chord members near the intersection zone of brace-chord behave as shell-like structures. The resulting flexibility may have significant effects on the local and overall behavior of offshore platforms. This study describes the derivation of a three-dimensional joint flexibility element which is based on physical interpretation of behavior of a tubular joint upon deformation. The element is developed on the basis of flexibility matrix and implemented in a finite element program to account for local joint flexibility effects in numerical models of jacket-type offshore platforms. Results are validated by more sophisticated multi-purpose software and compared against conventional rigid-joint models which are widely employed in practice. According to the results, the accuracy of response predictions is improved when the effects of joint flexibility are considered. This model can be used for predicting more accurate response of jacket-type offshore platforms. [ABSTRACT FROM AUTHOR]

Near field ground motions have caused several structural damages in recent decades. As a result, seismic codes are being updated with related requirements. In this paper a comparative study on the seismic behavior of concentrically braced frames (CBFs) designed based on different seismic codes is performed. Reliability of various frames with different heights and bracing types are analyzed based on the results of "Incremental Dynamic Analysis" (IDA) under near field ground motions. Fragility curves corresponding to 10 (Immediate Occupancy) and CP (Collapse Prevention) limit states are extracted based on IDA curves. Results imply that, frames designed based on the near field seismic design criteria of UBC-97 are more reliable under near field ground motions and their failure probability is less comparing to others. [ABSTRACT FROM AUTHOR]

The design of structures to withstand seismic loading is primarily governed by horizontal ground motion, and the effects of vertical ground motion have long been deemed unimportant or secondary. However, an emerging body of evidence suggests that vertical ground motions have great destructive potential, especially for certain site conditions.Using nonlinear dynamic analyses, the seismic performance of frames is evaluated by simultaneously applying the horizontal and vertical components of earthquake motion. Three special moment frames are subjected to 15 recorded near-field earthquake motions and the results of the analyses are used for performance evaluations, based on FEMA 350 guideline. It is found that, within the elastic range of response, considering the vertical component of ground motion, does not alter the dynamic structural response significantly, however, some tangible differences emerge in nonlinear range of response once the horizontal component of ground motion is accompanied by the vertical component. [ABSTRACT FROM AUTHOR]

Abstract: This paper introduces a new algorithm, namely the Extended Progressive Collapse Analysis (EPCA) algorithm, whose features, such as potential and capacity of buildings for occurrence of progressive collapse, were investigated. Their failure modes were determined by using pushdown and vertical incremental dynamic analyses. Moreover, by applying this procedure, the element removal impact factor and the most critical locations of such removals were obtained. This algorithm was utilized for progressive collapse analysis of two newly designed concentrically braced frames with different numbers and locations of braced bays in order to quantitatively determine its effect on mitigating progressive collapse. Using this method, the minimum residual capacity and the most critical locations of element loss as well as element removal impact factor for the frames that were studied were determined. Results showed that the frame with two braced bays had more robustness for mitigating progressive collapse, at least to the rate of 17.21% comparing to the frame with three braced bays. [Copyright &y& Elsevier]

Abstract: A new nonlinear two-dimensional tubular joint element is developed in this study on the basis of flexibility equations and the interaction between the axial force and the in-plane bending moment in the joint. Empirical equations are used to define the joint yielding in the axial direction and the in-plane rotation. An elastic–perfectly plastic yield function is adopted to include the combined effects of axial loads and bending moments on the yielding of the joint. The element formulation is straightforward, and it can readily be implemented in nonlinear finite element programs. Verification studies are carried out for the element to prove its suitability for the modeling of tubular joints of offshore jacket structures. It is concluded that the nonlinear joint model that has been developed produces accurate results, verified against experimental data as well as against sophisticated multi-axial finite element joint models. [Copyright &y& Elsevier]

Abstract: Earthquake hazards effect significant damage to structures and cause widespread failure throughout buildings. Moment resisting frames are widely used as lateral resisting systems when sufficient ductility is to be met. Generally three types of moment resisting frames are designed in practice namely Special, Intermediate and Ordinary Moment Frames, each of which has certain level of ductility. Comparative studies on the seismic performance of these three different types of structure are performed in this study. Analytical models of connections are employed including panel zone and beam to column joint model. Incremental dynamic analysis is then utilized to assess the structural dynamic behavior of the frames and to generate required data for performance based evaluations. Maximum annual probability of exceeding different limit states may reveal the superiority of a ductile structure in which a greater behavior factor is employed. Special moment resisting frames are expected to perform better once a certain level of ductility is to be met but the amount of superiority may be the subject of investigation especially from a performance based design standpoint. [Copyright &y& Elsevier]

Abstract: In this paper, pushover analysis of fixed jacket offshore platforms with the application of “Fiber Elements” which are capable of modeling post-buckling behavior of braces has been conducted and case study on two functional jacket offshore platforms in the Persian Gulf region has been performed. Two-dimensional models of the mentioned platforms are simulated using “DRAIN-3DX” software and the wave force is considered as the lateral load pattern on the structures. In this paper, pushover analysis of jacket offshore platforms is performed by developing numerical models that incorporate different foundation conditions for considering pile–soil-structure interaction. Increasing the displacement of the platforms and recording the relative load factors by incorporating the displacement control method is the basis for performing the analysis. In order to consider the importance of pile–soil interaction, six individual cases are examined which include pile–soil interaction analysis with actual soil in-situ characteristics. Pile head fixed below mud line elevation, pile head hinged below mud line elevation, application of linear pile stubs, application of non-linear pile-stubs & finally a combination of linear and non-linear pile–soil characteristics. In the analyses performed herein, the condition in which pile–soil interaction is considered is set to be the base case. The results from incorporating the non-linear pile stub have the most compatibility with the base case. Application of Linear pile stubs and the combination of linear and non-linear pile has much deviation with the base case. Ultimate strength of the platform in the non-linear pile stub case was very close to the base case. [Copyright &y& Elsevier]

• A newly designed post-tensioned self-centering yielding brace system is developed. • Experiments are conducted on a set of PT-SCYBS with different configurations. • Evaluation indices are proposed to examine the hysteretic response of the PT-SCYBS. • PT-SCYBS exhibits a desirable response with the self-centering capability. • A finite element baseline model is proposed and validated against the test results. This paper presents the results of an experimental study for a post-tensioned self-centering yielding brace system (PT-SCYBS). This newly designed bracing system is comprised of high-strength post-tensioned (PT) wires with highly ductile steel bars in parallel, providing an easy-to-construct supplemental device. A full-scale PT-SCYBS prototype was fabricated, and a set of PT-SCYBS specimens with different configurations are experimentally studied. The main objective of this paper is to examine the hysteretic response of the proposed PT-SCYBS by evaluating the effects of various parameters, including the number and diameter of PT wires and the diameter of steel bars, the post-tensioning ratio of PT wires, the loading protocol, and the loading rate. As confirmed by the experiments, the PT-SCYBS provides a repeatable flag-shaped hysteretic response with the self-centering capability, which would in turn, leads to a reduced residual displacement in this system. The experimental results show that increasing the post-tensioning ratio of the PT wires results in negligible residual displacements in the PT-SCYBSs. For the same post-tensioning ratio, when a specimen has a larger energy dissipation unit (i.e., a larger number of steel bars), it has a greater cumulative energy dissipation capacity and effective stiffness. Furthermore, the residual displacement of the PT-SCYBS can be controlled by changing the number and diameter of the PT wires and the steel bars' diameter. Finally, a nonlinear finite element baseline model is calibrated for the PT-SCYBS; and a good agreement has been observed between the experimental and numerical results. [ABSTRACT FROM AUTHOR]

Jacket platforms are widely used for hydrocarbon production in the oil and gas offshore field so far. After years of operation in jacket platforms, a structural integrity check is required to investigate whether the structure of the jackets is fit for purpose or not. So, maintenance, repair, and strengthening become an ongoing and continual process during the jacket platform's life. Corrosion, fatigue, vessel collisions, heavy dropped objects, and severe storms are the main reasons for damages. These events lead to perforation, dent, failure, and strength reduction of jacket elements. In this paper, a set of finite element models is used to model each damage case. Moreover, Strengthening, Modification, and Repair (SMR) techniques observe the members' behavior and the efficiency of the repair action. Also, multi-criteria analysis is presented for prioritizing the SMR techniques using the technique for preference by similarity to ideal solution (TOPSIS) method. The results and insights, the ultimate strength for both damage and repaired cases, provide a supportive view to the engineers to design a proper repair method. What is more, the results provide an ideal solution in selecting alternatives for repair methods. [ABSTRACT FROM AUTHOR]

Offshore structures usually are implemented in harsh environmental conditions which make the structures disposed to different failures. Negligible failures may lead to catastrophic ones. To prevent potential catastrophic failure, development of robust damage detection methods for offshore structures is necessary. Damages change structure's dynamic characteristics. Among different dynamic characteristics, modal frequencies and mode shapes are utilized more often. Due to various problems regarding damage detection methods for offshore structures such as sensor installation and data acquisition in water, damage detection methods using limited sensors seems very vital. In this paper, a novel method called Improved Modal Strain Energy Decomposition Method (IMSEDM) is developed to detect structural damage of jacket-type offshore platforms using a limited number of sensors just above the water. The proposed method has two main contributions. The first is simultaneous use of both modal frequencies and mode shapes which make damage detection more accurate. The second is decomposition of modal strain energy into axial and bending. IMSEDM locates damaged elements by considering the impacts of the damage on axial and bending modal strain energy. The method is evaluated using an experimental jacket type offshore platform. The results confirm that IMSEDM can effectively detect damages with incomplete data. • A new method for damage detection of jacket type offshore platforms. • Limited sensors above the water level to overcome data acquisition difficulties. • 2-directional acceleration sensors signal processing to extract modal data. • Expanding limited experimental modal data using numerical model in ABAQUS. • Demonstrating the method sensitivity to the distance between damages and sensors. [ABSTRACT FROM AUTHOR]

• A new optimization method called Search and Rescue optimization algorithm (SAR) is proposed. • SAR is tested on 13 constrained benchmark functions and CEC2010 benchmark functions. • Experiment results show superiority of SAR compared with other optimization methods. • SAR is also used for solving 7 engineering optimization problems. • The results on the engineering problems prove the performance of SAR in practice. A new optimization method namely the Search and Rescue optimization algorithm (SAR) is presented here to solve constrained engineering optimization problems. This metaheuristic algorithm imitates the explorations behavior of humans during search and rescue operations. The ε-constrained method is utilized as a constraint-handling technique. Besides, a restart strategy is proposed to avoid local infeasible minima in some complex constrained optimization problems. SAR is applied to solve 18 benchmark constraint functions presented in CEC 2010, 13 benchmark constraint functions, and 7 constrained engineering design problems reported in the specialized literature. The performance of SAR is compared with some state-of-the-art optimization algorithms. According to the statistical comparison results, the performance of SAR is better or highly competitive against the compared algorithms on most of the studied problems. [ABSTRACT FROM AUTHOR]

Semi-active control is one of the most effective methods for damage reduction in offshore platforms subjected to intense environmental forces. Despite its advantages, probable device time delays may drastically decrease the real performance of the control algorithm. Thus, the uncertainty could make the control process non-optimal. In this paper, a Kalman Filter is used to ponder previous responses and the history of the measured errors in order to estimate the real state variables of an offshore structure equipped with Magneto-Rheological (MR) dampers. In the current article, the amount of applied voltage to the MR damper is optimized via the Adaptive Particle Swarm Optimization (APSO) method. Furthermore, the structure is controlled by the Linear–Quadratic Regulator (LQR) algorithm. A newly installed offshore platform, located in the Persian Gulf at a depth of 64 m is considered as an example to demonstrate the performance of the controller. The offshore structure is assumed to be excited by near- and far-field earthquakes. The results of the parametric studies indicate that all the earthquake-induced vibrations of the platform can be effectively suppressed by the designed control system. Moreover, the life spans of the dampers may increase with the predicting-optimizing algorithm. A predictor-optimizing semi-active control system is designed to reduce structural responses of a fixed metal offshore platform equipped by horizontal MR dampers under earthquake excitations. The controller estimates the responses of the structure considering probable noises to reduce the time delays and inefficient actuator forces. In addition, the inlet voltages of the dampers are optimized to develop the dampers' duration and reduce the structural responses. Image 1 • Optimizing voltages of MR dampers placed on offshore platforms. • Structural state estimation for improving the efficiency of a control system. • Considering instrument noises and time delays to reach the real-time control. • Optimum-state estimating controller on a structure under far/near-field earthquakes. • Life span increase of semi-active Magneto-Rheological dampers. [ABSTRACT FROM AUTHOR]

Lognormal distribution is one of the most applicable distributions in many different probabilistic seismic assessments such as seismic hazard analysis, fragility analyses, and reliability evaluations. This study compares the sample median (SM), sample geometric mean (SGM) and Sample Bias Corrected Geometric Mean (SBCGM) as three different estimators of lognormal central estimator from different aspects. To this end, the efficiency of each estimator is investigated by calculating their bias and minimum squared error (MSE) using Monte Carlo Simulations. Further, probabilistic performance of four Steel Moment Resisting Frames (SMRF) is investigated using Incremental Dynamic Analysis (IDA), and the stochastic seismic performance of one of them (5 story frame) is investigated considering the aleatoric and epistemic uncertainties. Additionally, the probabilistic seismic performance of a sample jacket type offshore platform based on the mentioned statistical estimators of lognormal central tendency is investigated implementing the IDA procedure. The results show that the efficiency of SM is significantly lower than the other two estimators. In general, SBCGM is the most efficient one for small sample sizes. However, SBCGM and SGM show the same efficiency as the sample size increases. Also, noticeable differences can be observed in the seismic performance of the structures based on each estimator. According to the results of goodness of fit tests and the likelihood ratio evaluations, SBCGM is recommended for achieving more reliable seismic assessments when using small number of records. As another marginal conclusion, the conducted statistical study revealed that the lognormal assumption is approved for collapse fragility curves considering both aleatoric and epistemic sources of uncertainty. [ABSTRACT FROM AUTHOR]

A novel approach to damage detection based on dispersion analysis and signal processing methods is described. The proposed method was used on a scaled experimental model of a jacket-type offshore platform. A forced vibration test was conducted on the platform to acquire the acceleration signals. The frequency spectrum of the first intrinsic mode function of the recorded signals was obtained by the Hilbert transform (HT); it was found that damage engendered dispersion in the extracted frequencies. A novel damage index, capable of accurate damage detection and based on the Mahalanobis distance dispersion of the HT frequency spectrum was thus developed. The results of this work show that the proposed index can determine the location and severity of damage with acceptable accuracy. [ABSTRACT FROM AUTHOR]

Fixed offshore platforms in seismic active areas may be subjected to strong ground motions, causing the platform to undergo deformation well into the inelastic range. In this paper, incremental dynamic analysis (IDA) of jacket type offshore platforms subjected to earthquake was performed in order to study the linear and nonlinear dynamic behavior of this type of structures. IDA is a parametric analysis method that has been recently presented to estimate structural performance under seismic loads. By using incremental dynamic analysis of jacket type offshore platforms, the assessment of demand and capacity can be carried out. The method was used to predict nonlinear behavior of three newly designed jacket type offshore platforms subjected to strong ground motions. The engineering demand parameters of the platforms in terms of story drifts and intermediate elevation maximum displacement for different records were compared. This method was used for the performance calculations (immediate occupancy, collapse prevention, and global dynamic instability) needed for performance-based earthquake engineering of the above mentioned platforms. Two different behaviors were observed for the third platform in the X and Y directions. Particular attention has to be paid for the seismic design of this kind of platform. The results of jacket type offshore platforms incremental dynamic analysis shows that the method is a valuable tool for studying dynamic behavior in a nonlinear range of deformation. Because of high uncertainty in the nonlinear behavior of this type of structures, it is recommended to use this method for the assessment and requalification of existing jacket type offshore platforms subjected to earthquake. [ABSTRACT FROM AUTHOR]

With the help of Structural Health Monitoring (SHM) methods, it is possible to identify the occurrence of damage at its early stages and prevent fatality and financial damages. Great advances in signal processing methods in combination with Machine learning tools have led to better achieve this goal. In the present paper, the two major techniques, that is, Empirical Mode Decomposition (EMD) and Discrete Wavelet Transform (DWT) are combined with Artificial Neural Network (ANN) through processing raw acceleration responses measured on a scaled jacket type offshore platform which was constructed and tested as a benchmark structure at K.N. Toosi University of Technology. In this way, ANN was trained by the signals obtained from EMD and DWT for three different conditions of the jacket platform to determine the relative damage severity. The envelope of the obtained signal's energy (ENV) as an appropriate damage index was used to determine the damage location. The results of the application of this procedure on the case study indicated that DWT, compared to EMD, is a more reliable signal processing method in damage detection due to better noise reduction. [ABSTRACT FROM AUTHOR]