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This study proposes a hydroelastic optimization method for multiseparated modules of high-specific-strength floating structures with low-weight cores and high-strength surfaces in two-dimension. A sixth-order dynamical model of this floating composite structure is deduced from the fluid-structure interaction condition of the wave surface. Drawing upon potential flow theory and separation of variables, we discretize the water domain into plate-covered areas and open water areas, in which the analytical solution for the interaction between waves and the floating composite structure with any number of separated modules is derived. The convergence and accuracy of the analytical solution are verified by calculating the transmission and reflection coefficients of the waves and various hydrodynamic parameters, including deflection, bending moment, and shear force. Furthermore, the effects of the number of modules, module spacing, and core thickness on the hydrodynamic parameters of the floating structure are investigated. The module number and structural-component-material parameters are coupled in influencing the hydroelastic behavior and mechanical responses of this floating cluster. This proposed method is an alternative optimization technique for considering the sea state, spatial modules, structural features and material properties in practical engineering applications. • A hydroelastic optimization method for multiseparated modules of high-specific-strength floating structures was proposed. • The interaction between waves and the floating structure with any number of separated modules is derived. • The structural-component-material parameters are coupled in influencing the hydroelastic and mechanical behaviors. [ABSTRACT FROM AUTHOR]

This paper presents the fatigue reliability prediction for welded planar tubular joints of offshore fixed jacket support structures. A coupled model is employed to calculate the dynamic response of the jacket support structure under wind and wave loads. Stress concentration factors (SCFs) are evaluated using Efthymiou parametric equations, and the hot-spot stresses at eight locations on the chord and brace of the tubular joints are derived by summing the stress components from axial, in-plane, and out-of-plane actions. The stress distribution is determined using the rainflow counting method, fatigue damage from an S–N curve, and Miner's rule. Uncertainties associated with the fatigue lifetime evaluation procedure are identified, quantified, and modeled. The focus is specifically given to modeling the uncertainty related to the SCFs, and a framework is proposed to evaluate the fatigue reliability of the joint by incorporating individual uncertainties for each degree of freedom of the SCFs (i.e., axial load crown, axial load saddle, in-plane bending moment, and out-of-plane bending moment). The results reveal that assuming the same uncertainty level (Coefficient of Variation of 0.2) as recommended by DNV-RP-C210 for each degree of freedom of the SCFs and including the uncertainty after obtaining the stress distribution from rainflow counting does not consistently yield conservative reliability index values, as it depends on the critical hot spot. It is essential to note that the simplified assumptions derived from the oil and gas sector may not directly translate to the offshore wind industry due to differences in loading conditions. A reduction of up to approximately 24% in the reliability index is observed for one critical hot spot, while an increase of up to 20% was observed for another. Overall, this paper provides valuable insights into the complex interplay of factors affecting the reliability of joints in offshore fixed jacket support structures, shedding light on the need for tailored approaches to address uncertainties in the specific context of the offshore wind industry. • Fatigue reliability of welded tubular joints in offshore wind turbine (OWT) jacket. • The stress distribution is determined using the rainflow counting method. • Fatigue damage is assessed using an S–N curve and Miner's rule. • Incorporates individual uncertainties for each degree of freedom (DOF) of SCFs. • SCFs uncertainty most impacts hot spot reliability index in OWT jacket joints. • The same uncertainty in each DOF of SCFs does not ensure conservative reliability. [ABSTRACT FROM AUTHOR]

Glass fiber reinforced polymer (GFRP) has been applied in hull structures for small and medium-size ships due its lightweight, high strength and easy fabrication. When the action load coming from the ship self-weight and the ocean environment becomes extremely large, the GFRP hull structure may present special failure modes and their evolution processes. How to define the ultimate strength study for GFRP hulls is a critical issue for vessel safety design. In this paper, one GFRP girder to represent the structural properties of the actual hull structure is selected as the research object. The GFRP girder is made of plates of varying thickness strengthened by hat stiffeners and foam. The hat stiffener, its attaching plate and core foam are made using an integral vacuum forming technique to avoid local construction defects. The sectional corners of the GFRP girder are provided with sufficient support by a combination of adhesive bonding and bolt secure connections. The failure experiment for the GFRP girder is performed on a four-point bending facility with a single hydraulic actuator to apply the bending moment. The strain variation is recorded by the digital image correlation (DIC) system on deck upper surface and 42 strain gauges on other critical regions. The deformation data is measured by 11 displacement sensors during a step-like increase of the applied load. The deformed shape are also recorded by the DIC system and the camera. Based on the experimental results, curves of the applied load and structural displacement are plotted to obtain the ultimate strength of the experiment girder. The failure modes and their evaluation processes are also discussed based on the video recordings. Finally, the failure process of the experiment GFRP girder is simulated using the nonlinear finite element method to study the effect of local delamination at various locations where the ultimate strength is determined. Both the experimental results and direct calculations demonstrate that the GFRP girder may exhibit a kind of brittle failure after the limit load point. The conclusions obtained in this paper will provide a guide for the design of GFRP ships and the modification of ship rules. • Investigation of failure modes and ultimate strength of composite structure under bending load. • A thin-walled girders made of GRRP is investigated by an model experiment and numerical studies. • The corner connection with foam and adhesive layer has sufficient strength during the experiment loading. • The FE method in this paper can give a consistent evaluation of ultimate strength as the experiment. • The adhesive layer is a critical region for the connection of composite structure. [ABSTRACT FROM AUTHOR]

Models used in hydro-elastic experiments should not only reflect the geometries of the hull form, but also the elastic characteristics of the prototype. Two types of models have been generally developed for this purpose: segmented and fully elastic models. When scaling sectional properties, most studies have only considered similarity in the vertical bending mode. Container ships may also experience high torsional moments in addition to vertical bending moments, because of their large openings on the deck. To investigate the various hydro-elastic response of container ships, we develop and present a fully elastic ship-shape model in this study. Applying a novel structural design with internal structures resembling a container ship allows the vertical bending, horizontal bending and torsional vibration modes to be similar to those of a prototype container ship. Strain gauges instrumented throughout the model measure the hydro-elastic structural response including vertical bending moment, vertical shear force, and torsional moment. We studied the elastic parameters of the model comprehensively through a series of experiments and further tested the model in different wave conditions and forward speeds through wave experiments. We found the measured global structural responses agree with those of numerical simulations. The methodologies developed in this study provide new insights into how to design a fully elastic model which can be used to investigate the hydro-elastic responses of container ships. • Fully elastic ship-shape model with internal structures resembling a container ship. • Strain gauges instrumented at various locations are calibrated through static tests. • Structural dynamic properties identified with impact hammer test, and compared with numerical models. • Model towed both in head sea and oblique sea environments. • Hydro-elastic response measurement including vertical bending moment, vertical shear force, and torsional moment. [ABSTRACT FROM AUTHOR]

An improved scaled method for box girders subjected to a hogging moment is developed based on maintaining the similarity of section properties and slenderness. The section area, moment of inertia, section modulus, plate slenderness, and column slenderness are considered as factors influencing the determination of the ultimate hogging moment. A smaller scale ratio is required to reduce the load-carrying capacity of scaled models, which poses challenges in ensuring that the designed scaled model aligns with the requirements of the construction process. Based on the discussion of several design strategies, a reasonable design of scaled models can be achieved through the following steps. First, the similarity of the plate slenderness is maintained by adjusting the number of stiffeners. Secondly, the similarity in column slenderness is maintained by adjusting the plate length. Third, the similarity of the section properties is improved by maintaining the similarity of the area of the local part. Simultaneously, the scaling strategy of the stiffeners is changed to ensure the similarity of the collapse modes. Fourth, modification methods for the similarity of the moment of inertia and section modulus are proposed to further improve the similarity of the ultimate bending moment. Furthermore, the criteria for choosing a modification of the section modulus and moment of inertia were proposed. • A comparative analysis on typical scaling strategies was conducted. • An improved scaled method of the box girders subjected to a hogging moment was proposed based on the similarity in the slenderness and section properties. • A method to improve the similarity in section modulus and moment of inertia was proposed based on the theoretical derivation. • A selection criterion for achieving similarity in the moment of inertia or section modulus was proposed based on the stress level of the deck plate. [ABSTRACT FROM AUTHOR]

A good understanding of cross-sectional loads of the support structures of floating wind turbines (FWTs) serves as a basis for achieving a reasonable floater design to ensure its safety and reliability over the lifetime at a low cost. While many studies have investigated global motion responses of FWTs, minimal attention has been directed toward the structural load effect analysis of the support structures. This paper deals with an experimental study of a 5-MW semi-submersible FWT in shallow water, in which a multi-segment hull is manufactured to measure the internal cross-sectional loads of the floater based on strain measurements. Model tests of the FWT are carried out at a 1:50 scale in a wave basin under multiple environmental conditions to investigate the characteristics of global dynamic responses of the FWT and internal cross-sectional loads of the hull. The results unveil that the vertical bending moment of the hull's cross-section is notably influenced by resonant responses in heave and pitch motions, as well as the platform motions within the wave-frequency region. Conversely, the horizontal bending moment remains impervious to resonant responses of the hull in the low-frequency range and is mainly governed by platform motions in the wave-frequency region. In addition, the wind loads also exert a certain influence on the vertical bending moment of the hull, but have limited impact on the horizontal bending moment. This paper contributes to establishing enhanced model test methods and provides a basis for improving the design and analysis of semi-submersible hulls of FWTs. • An experiment study of a semi-submersible FWT with a multi-segment hull under shallow water. • An FBG-based method was used to measure the internal structural loads of the hull. • Both global responses and internal structural loads of the hull are analyzed. • Nonlinear wave-induced responses are addressed under bi-chromatic and extreme wave conditions. • Correlation between platform motion and internal cross-section loads of the hull is revealed. [ABSTRACT FROM AUTHOR]

A novel theoretical model is proposed to study the continuum damage mechanical (CDM) behavior of reinforced thermoplastic pipes (RTPs) under bending moments, in which stress analysis of composites, failure evaluation and stiffness degradation are combined in loop calculation. Based on the existing homogenization assumption, the stress distribution of every ply could be calculated according to the equilibrium equations between the RTP and a hypothetical homogenous pipe. Once stresses of composite plies satisfy Hashin-Yeh failure criterion, dominant failure modes are determined by filtering failure coefficients. Subsequently, the stiffness degradation model would be performed, in which a sine weight function is employed to consider the damage distribution along the hoop direction. Meanwhile, the von Mises criterion and Ramberg-Osgood curve are used to simulate the material nonlinearity of liner and coating. Four-point bending tests and numerical simulations were conducted to verify the proposed theoretical model. A user-defined VUMAT subroutine was employed to simulate the progressive failure of 3D composites. Compared with experimental tests and numerical simulations, the proposed model could give accurate predictions on the linear and nonlinear responses, such as the bending stiffness, the stress field and the damage propagation. Furthermore, different methods for the four-point bending test were also compared and good correlation found. • A theoretical continuum damage model is proposed to study the progressive failure of RTPs under bending moments. • Four-point bending tests were conducted on 6 RTP specimens. • A user-defined VUMAT subroutine was employed in the four-point and pure bending simulations. • Experimental, analytical and numerical results agreed well. • Different methods for the four-point bending test were also compared and discussed. [ABSTRACT FROM AUTHOR]

are presented of a benchmark study organised by the Marstruct Virtual Institute on motion and global wave loads on a warship model in regular waves. The aim of the study is the quantification of the uncertainty in numerical whipping predictions. Nine institutions participated in the benchmark with 6 codes, quantifying the hydroelastic responses. The seakeeping methods employed include non-linear strip theory, 3D boundary element method formulated in frequency and time domain, and computational fluid dynamics (CFD). Euler and Timoshenko beams are used for modelling the hull girder stiffness. Experimentally based methods, CFD and momentum theories are employed for calculating slamming loads. The study encompasses a comparison of wet natural frequencies of ship vertical flexural vibration, vertical ship motions, vertical wave bending moments and whipping bending moments at midships. Wave-induced and whipping responses are analysed for regular head waves of different steepness and for two ship speeds. For most comparisons, experimental results are available from previously performed and published model-scale experiments on a Canadian Patrol Frigate. Frequency-independent model error, which is commonly used for uncertainty quantification of rigid body seakeeping responses is extended to quantify uncertainties in whipping bending moments. It is found that fully coupled CFD and finite element method (FEM) provide results consistent with measurements, but such simulations are prohibitively computationally expensive and the interpretation of results can be challenging. The combination of the potential theory seakeeping method with correction based on CFD-FEM simulation for limiting number of cases is a promising alternative. • Results are presented of a benchmark study on motion and global wave loads on a warship model in regular waves. • The aim of the study is the quantification of the uncertainty in numerical whipping predictions. • Nine institutions participated in the benchmark with 6 codes, quantifying the hydroelastic responses. • Only methods using fully coupled CFD and FEM provide results consistent with measurements the combination of the potential theory seakeeping method coupled with CFD-FEM simulation is a promising alternative. [ABSTRACT FROM AUTHOR]

The present paper deals with a systematic study of the shear lag effect on the bending moment distribution in girders of representative pontoon-type floating bridges (PTFBs). Comparative and parametric studies for well-developed beam and linear shell models for representative structural components of a reference PTFB subject to representative static and dynamic loads, e.g. self-weight load condition, traffic loads, and wave-induced vertical dynamic loads on PTFB's pontoons are carried out. The study is partly based on a simplified, generic PTFB model, denoted GPTFB. The study shows that elementary beam element models, for which shear lag effects are not accounted for, might, to some extent, inaccurately predict the bending stiffness, eigenmode shapes and eigen frequencies of PTFBs with large width and relatively short span lengths (e.g. the ratio of span length to girder width of PTFBs is less than 7.24), while the inaccurate prediction of beam model in weak axis bending moment in girder of the PTFBs is related to the load pattern and dynamic load frequency range. A practical method is proposed to judge when caution is needed in using elementary beam model for estimating the weak axis global bending moments in girder of PTFBs. In addition, a case study presented in this paper, shows that the part of the girder near the bank abutment might be subjected to complex boundary conditions since the girder is supported by floating pontoons and bottom fixed columns. In this part of the bridge girder, a significant influence of shear lag on weak axis bending moments is observed. Further analysis by using shell elements is necessary to estimate the stresses, including the effect of shear lag, in this part of the girder. • This paper extends shear lag study to statically indeterminate boundary conditions and dynamic behavior. • Well-developed beam and linear shell models for representative cases are systematically analyzed to show shear lag effect. • It finds shear lag makes weak-axis bending stiffness of floating bridge girders different to that of elementary beam theory. • It finds shear lag makes eigenmode frequency and shape of floating bridges different to that of elementary beam theory. • It finds shear lag makes weak-axis bending stiffness of floating bridge girders different to that of elementary beam theory. • It finds shear lag is related to structural boundary conditions, structural geometry and the spatial load pattern and frequency. • It finds shear lag decreases with increasing ratio of effective length to girder width. • A case study shows shear lag decreases to negligible level by increasing effective length to girder width ratio to 7 or more. • Shear lag effect on bending moment, fatigue and extreme response of a curved floating bridge under wave loads is analyzed. • A method is proposed to judge when shear lag effect needs to be accounted for in global dynamic analysis. [ABSTRACT FROM AUTHOR]

During service period, offshore wind turbines are subjected to both monotonic and cyclic loads, causing the rotation or translation of caisson foundations in the seabed. However, most of the existing studies focused on the performance of caisson foundations under monotonic static loading, and there are few studies about the effects of caisson-soil contact mode and soil strength reduction during installation in numerical simulations. This paper therefore systematically investigates the bending moment capacity and failure mechanism of caisson foundations under monotonic and cyclic loading in clay using finite element analyses. Three typical caisson-soil contact modes in different loading scenarios are considered, and the influence of soil strength condition, caisson aspect ratio on the bending moment capacity and failure mechanism of caisson foundations is explored. It is found that under monotonic loading, the bending moment capacity in the tensionless mode and the fully-bonded mode could be used as the lower and upper limit, respectively. Under cyclic loading, the fully-bonded mode always yields the highest moment capacity, while the frictionless mode and the tensionless mode produce the lowest in the case with small loading amplitude and the case with large loading amplitude, respectively. In addition, the behavior of cumulative angular displacement under combined load of wind and wave is also studied to provide insight for caisson foundation design. • The mechanical response of caisson foundation subjected to both monotonic and cyclic loading is numerically investigated. • Three typical caisson-soil contact modes in different loading scenarios are considered. • Recommendations in the design of caisson foundations under different loading conditions are provided. [ABSTRACT FROM AUTHOR]

The rapid growth of marine renewables has led to the development of very large floating structures (VLFS) that are designed to operate in deep seas. It is significant to understand the mechanism of the coupled effects between deformable VLFS and catenary mooring system. This paper presents a time-domain hydro-elastic-moored model developed by integrating a quasi-static mooring module into a fully coupled Computational Fluid Dynamics (CFD) - discrete-module-beam (DMB) approach. The model is used to investigate the coupled effects between structural hydroelasticity and loose-type mooring systems on a deformable VLFS in waves. The mooring and hydroelasticity codes are validated separately and show favourable agreement with other numerical and experimental results. Then the coupled effects between the mooring system and structural hydroelasticity are evaluated by assigning various design parameters, i.e., VLFS structural stiffness and mooring stiffness. The numerical results, including dynamic motions, longitudinal vertical bending moments (VBMs) and mooring tension forces are presented and analysed. These results can be used to design a VLFS with mooring in medium-deep sea, and help with the conventional mooring design for a less-stiffness VLFS due to hydroelastic response. • Quasi-static mooring in 2-way FSI studies VLFS-catenary mooring hydroelasticity. • VLFS's loose mooring system is evaluated in different wave conditions. • It is shown that VLFS structural elasticity significantly affects mooring tensions. [ABSTRACT FROM AUTHOR]

In this article, the seismic response of four different Offshore Wind Turbines (OWTs) from 5 to 15 MW, founded on monopiles embedded in homogeneous and non-homogeneous soil profiles with equivalent shear-wave velocities from 100 to 300 m/s is analysed. Two types of variable soil profiles with a semi-parabolic variation of the shear-wave velocity as depth increases are considered. The system seismic response under ten different accelerograms is computed through a finite element substructuring model in frequency domain. The foundation behaviour is obtained by a continuum model including kinematic and inertial interaction. Several models, in addition to that of rigid base condition, are considered to determine the influence of soil-structure interaction (SSI), as well as the contribution of each kinematic interaction (KI) factor. The seismic response of the OWTs is obtained in terms of maximum shear forces and bending moments at mudline level, as well as the acceleration amplification factor at hub level. It is found that the maximum response is produced when SSI is considered, including both the inertial and kinematic interaction. The differences arising due to the soil profile definition are shown to be mainly related to the rotational KI factor, which significantly affects the second vibration mode of the system. The largest responses are obtained for the homogeneous equivalent profile. • The seismic response of monopiled OWTs on different seabed profiles is studied. • The effects of SSI and of each KI factor on the seismic response are analysed. • Higher responses are obtained when a homogeneous profile and SSI are considered. • KI only has a significant effect if the rotational KI factor is taken into account. • The influence of the soil profile arises when the rotational KI factor is included. [ABSTRACT FROM AUTHOR]

This paper proposed a simplified formula for the long-term maximum wave-induced vertical bending moment (VBM) of ships. First, as a general theory independent of the type of ship response, the relationship between the long-term response and the peak value of the response amplitude operation (RAO) was discussed and its governing factors were clarified, and the methodology of the simplified formula development approach was presented. In particular, if the RAO has two properties, " band parameter-invariance " and " peak value-wavelength correspondence, " the long-term response can be expressed by only the peak value of RAO. Based on this approach, a simplified formula for the long-term maximum VBM was presented. First, focusing on the characteristics of the VBM-RAO in the case of zero speed, a formula with zero speed was derived, and based on this, a formula with a speed of 5 knots was derived. These formulae were validated by comparison with the results of a numerical analysis using 154 actual merchant ship models. The proposed method for developing the simplified formula is physically clear and is valid for all types of ships and responses. • A simplified formula for the linear long-term maximum response of ships in a general form, regardless of the ship type and size, is presented. • The long-term response corresponds to the peak value of the response amplitude operator (RAO). • The formula is expressed very simply when the non-dimensional RAO has two characteristics: band parameter-invariance and peak value-wavelength correspondence. • Simple and accurate formulae of long-term vertical bending moment were derived for the 0 knot and 5 knots cases. [ABSTRACT FROM AUTHOR]

Abstract The fatigue life of tubular joints commonly found in offshore structures is not only dependent on the value of hot-spot stress (HSS), but is also significantly influenced by the through-the-thickness stress distribution characterized by the degree of bending (DoB). In the present research, data extracted from the finite element (FE) analyses carried out on 81 two-planar tubular DT-joint models was used to study the effects of geometrical parameters on the DoB values in DT-joints subjected to six different types of loading including two types of axial loading, two types of in-plane bending (IPB) moment loading, and two types of out-of-plane bending (OPB) moment loading. Generated FE models were validated using available parametric equations. The determination of DoB values in a tubular joint is essential for improving the accuracy of fatigue life estimation using the stress-life (S N) method and particularly for predicting the fatigue crack growth based on the fracture mechanics (FM) approach. Geometrically parametric investigation was followed by a set of nonlinear regression analyses to develop three DoB parametric formulas for the fatigue analysis and design of two-planar DT-joints. Highlights • Geometrical effects on the DoB values in two-planar tubular DT-joints were studied. • Altogether, 81 FE models were generated and analyzed to extract the DoB values. • Six types of axial, IPB moment, and OPB moment loadings were considered for the parametric investigation. • A set of fatigue design equations was developed for the calculation of the DoB in two-planar DT-joints. [ABSTRACT FROM AUTHOR]

Abstract A linear model for efficient design evaluation of spar floating wind turbines is presented, and verified against a nonlinear time domain model with regards to long-term fatigue and short-term extreme response for two different spar designs. The model uses generalized displacements and a semi-analytical approach to establish the equations of motion for the system, which are solved in the frequency domain. The results show agreement within ± 30% for the long-term fatigue considering operational conditions, however, the linear fatigue damage estimates are sensitive to the accuracy of the estimated natural frequency of the first bending mode. The results also suggest that a small number of environmental conditions can be simulated with a nonlinear time domain model to verify and possibly tune the linear model, which then can be used to run the full long-term analysis. Short-term extreme tower base bending moments and surge and pitch motions are observed to be nearly Gaussian above cut-out wind speed, as the response is dominated by wave forces. Consequently, the linear model is able to accurately capture the upcrossing rates, which are used to calculate the characteristic largest extreme response. For an operational case near rated wind speed, the response is somewhat non-Gaussian, which gives larger discrepancies between the linear and nonlinear models. However, due to large mean values in this condition, the total error in the extreme response is reduced, and reasonable agreement is achieved. Highlights • A linear frequency domain model for spar floating wind turbines has been developed. • The model has been compared to a nonlinear time domain model. • Good agreement for tower fatigue, but results were sensitive to first bending mode. • The largest short-term extreme response were found near rated wind speed. • Extreme response were nearly Gaussian above cut-out wind-speed. [ABSTRACT FROM AUTHOR]

Abstract Probability distribution models are essential for the reliability-based analysis and design of offshore structures. The objective of the present research was developing a probability distribution model for the local joint flexibility (LJF) factor, f LJF , in two-planar tubular DK-joints commonly found in jacket-type offshore wind turbines and oil/gas production platforms. A total of 324 finite element (FE) analyses were carried out on 81 FE models of DK-joints subjected to four types of out-of-plane bending (OPB) moment loads. Generated FE models were validated using the available experimental data, FE results, and design formulas. Based on the results of parametric FE study, a sample database was prepared for the f LJF values and density histograms were generated for respective samples based on the Freedman-Diaconis rule. Nine theoretical probability density functions (PDFs) were fitted to the developed histograms and the maximum likelihood (ML) method was applied to evaluate the parameters of fitted PDFs. In each case, the Kolmogorov-Smirnov and chi-squared tests were used to evaluate the goodness of fit. Finally, the lognormal model was proposed as the governing probability distribution function for the f LJF. After substituting the values of estimated parameters, four fully defined PDFs were presented for the f LJF in tubular DK-joints subjected to four types of OPB moment loads. Highlights • 324 FE analyses were conducted to investigate the local joint flexibility of two-planar tubular DK-joints. • Four types of OPB loading were considered for the parametric study. • Extracted data was used to develop a probability distribution model for the f LJF. • The lognormal model was selected as the best-fitted distribution. • Four fully defined PDFs were proposed for the f LJF of OPB-loaded two-planar tubular DK-joints. [ABSTRACT FROM AUTHOR]

Abstract Monopiles are currently the preferred option for supporting offshore wind turbines (OWTs) in water depths up to about 40 m. Whilst there have been significant advancements in the understanding of the behaviour of monopiles, the guidelines on the prediction of long term tilt (Serviceability Limit State, SLS) under millions of cycles of loads are still limited. Observations and analysis of scaled model tests identify two main parameters that governs the progressive tilt of monopiles: (a) Loading type (one-way or two-way) which can be quantified by the ratio of the minimum to maximum mudline bending moments (M min /M max); (b) factor of safety against overturning i.e. the ratio of the maximum applied moment (M max) to the moment carrying capacity of the pile or Moment of Resistance (M R) and therefore the ratio M max /M R. Due to the nature of the environmental loads (wind and wave) and the operating conditions of the turbine, the ratio M min /M max changes. The aim of this paper is to develop a practical method that can predict the nature of loading for the following governing load cases: Normal Operating Conditions, Extreme Wave Load scenario, and Extreme Wind Load scenario. The proposed method is applied to 15 existing wind farms in Europe where (M min /M max) and (M max /M R) are evaluated. The results show that the loading ratio is sensitive to the water depth and turbine size. Furthermore, under normal operating conditions, most of the wind turbine foundations in shallow waters are subjected to one-way loading and in deeper waters and under extreme conditions the loading is marginally two-way. Predictions for the nature of loading for large wind turbines (8 MW and 10 MW) in deeper waters are also presented. The results from this paper can be used for planning scaled model tests and element tests of the soil. Highlights • Deterministic methodology to calculate minimum (M min) and maximum (M max) moments on a monopile due to wind and wave loads. • Range of M min /M max for 15 operating wind turbines in normal operating conditions and extreme conditions. • Prediction of (M min /M max) for large wind turbines in deeper waters. [ABSTRACT FROM AUTHOR]

For piggyback pipelaying operations, current-induced force and its effect on the piggyback pipe have not been thoroughly studied. In the present study, an improved method in hydrodynamic load calculation and structural modelling is proposed to simulate the pipelaying of a piggyback pipeline. In order to obtain the mean drag and lift force coefficients for the piggyback pipeline subjected to different inflow angles, two-dimensional Computational Fluid Dynamics (CFD) simulations are performed by modelling the piggyback pipeline as two cylinders attached to each other without gap. Then, the acquired force coefficients are used to calculate the hydrodynamic loads through a user-defined function in OrcaFlex based on a cross-flow principle approach. The interaction between the pipeline and the piggyback cable is modelled using two types contact elements which are ring penetrator and non-penetrating contact. The present proposed method is compared with other two widely used engineering methods based on (1) the equivalent diameter and (2) two separate cylinders without accounting for hydrodynamic interaction, in terms of the top tension, and the bending moments at Hang-off Clamps (HOC) and sagbend of the pipeline. The comparison shows that the two widely used engineering methods are not always conservative in force and response predictions. Hence, it is important to consider the hydrodynamic and structural interactions between the piggyback cable and the pipeline. With different current directions, the bending moments at the HOC predicted by the present method vary from 40% lower to 100% higher than those predicted by the two widely used engineering methods. • The influence of piggyback pipeline modelling methods on the calculation of installation loads in deepwater is investigated. • An improved method that considers the interactions between the pipeline and the piggyback cable is proposed. • Drag and lift coefficients on the pipeline and piggyback cable are computed using 2D CFD simulations of flow past two adjacent smooth circular cylinders. • A user-defined function is implemented to calculate the hydrodynamic forces on the pipeline and the piggyback cable. • The proposed model can capture the hydrodynamic and structural interactions between the pipeline and the piggyback cable. [ABSTRACT FROM AUTHOR]

Marine engineering structures may be subjected to various levels of vessel collisions, causing different degrees of damage to the RC piles. However, the influence of different combinations of impact mass and velocity under the same initial kinetic energy or momentum on the impact behavior of RC piles has not been explored. A numerical investigation of the impact responses of RC pile structures (including plumb piles and inclined pile groups) considering the material strain rate effect is carried out using the software ABAQUS/Explicit in this paper. Parametric studies are conducted based on the validated finite element models of RC piles subjected to horizontal impact. The internal force distributions, as well as the effect of the impact kinetic energy and the momentum (including different combinations of impact mass and initial velocity) on the impact response of RC piles, are discussed. The results indicate that the development path of the bending moment‒overall structural displacement curves in the plastic hinge regions of RC piles are almost identical under both impact and static loading conditions. Compared to momentum, the impact response of RC piles is insensitive to the variation of impact kinetic energy with different combinations of impact mass and velocity. Therefore, the impact kinetic energy is more suitable for evaluating the structural deformation of RC piles after impact. Finally, a performance-based impact-resistance design framework for RC piles is proposed. • A numerical investigation of the impact responses of RC pile structures is carried out. • The internal force distributions on the impact response of RC piles are discussed. • The effect of different combinations of impact mass and initial velocity on the response of RC piles is studied. • A performance-based impact-resistance design framework for RC piles is proposed. [ABSTRACT FROM AUTHOR]

The concept of a shared mooring system was proposed to reduce mooring and anchoring costs. Shared moorings also add complexity to the floating offshore wind farm system and pose design challenges. To understand the system dynamics, this paper presents a dynamic analysis for a dual-spar floating offshore wind farm with a shared mooring system in extreme environmental conditions. First, a numerical model of the floating offshore wind farm was established in a commercial simulation tool. Then, time-domain simulations were performed for the parked wind farm under extreme wind and wave conditions. A sensitivity study was carried out to investigate the influence of loading directions and shared line mooring properties. To highlight the influence of the shared line, the results were compared to those of a single spar floating wind turbine, and larger platform motions and higher tension loads in single lines are observed for the wind farm with shared moorings. The loading direction affects the platform motions and mooring response of the floating offshore wind farm. Comparing the investigated loading directions to the 0-deg loading direction, the variation of mean mooring tension at the fairlead is up to 84% for single lines and 16% for the shared line. The influence of the shared line properties in the platform motions and the structural responses is limited. These findings improve understanding of the dynamic characteristics of floating offshore wind farms with a shared mooring system. • A shared mooring system is applied to a dual-spar floating offshore wind farm. • Extreme wind and wave conditions are considered in the dynamic analysis. • Dynamics of the wind farm is compared with that of a single floating wind turbine. • Mooring stiffness linearization is performed to elucidate physical characteristics. • Mooring tension, tower-bottom bending moment, and platform motions are analyzed. • The influence of loading directions and shared line properties on responses is shown. [ABSTRACT FROM AUTHOR]

Internal solitary waves with a huge amount of energy easily trigger the large dynamic responses of riser-wellhead system and threaten its structural safety. However, previous studies have only focused on the dynamic response of the riser under internal solitary waves. The riser may experience excessive traction from the platform, especially from the mooring platform, in response to the arrival of internal solitary waves. The bottom of the riser connects to the wellhead system, which in turn exerts a reaction force on the riser. To address this problem, a coupled dynamic model of deep-water drilling mooring platform-riser-wellhead system under internal solitary waves is developed in this paper. A dynamic response analysis method based on the fourth-order Runge-Kutta method and finite element method is also proposed for the mooring platform-riser-wellhead system. A dynamical solver for the coupled system is then developed using MATLAB. The dynamic response characteristics of the riser-wellhead system under internal solitary waves are calculated. Results show that the displacement and bending moment of the system initially increases and then decreases along with the propagation of internal solitary waves, and finally reach equilibrium position. The displacement and bending moment reach their peak before the trough of internal solitary waves passes through the riser-wellhead system. The dynamic responses of the riser-wellhead system under the influence of internal solitary wave loads are much larger than those without the effect of internal solitary wave loads. The riser system experiences shearing loads at the interface of internal solitary waves, which trigger a step-like bending moment variation. The bending moment of the conductor under the mudline is greatly increased by the internal solitary waves. • A coupled dynamic model of deep-water mooring platform-riser-wellhead system under internal solitary waves is developed. • A dynamic response analysis method for the coupled dynamic model is proposed. • The dynamic responses reach their peak with the influence of the trough of internal solitary waves. • The riser-wellhead system has much larger dynamic response under the internal solitary wave loads. • The bending moment of the riser at the interface of internal solitary waves has a "step"-like form. [ABSTRACT FROM AUTHOR]

A model of a composite-to-steel hybrid balcony overhang is tested to find its strength and stiffness under imposed shear and bending loads. The configuration tested is representative of a solution being considered for the balconies of cruise ships, where the substitution of steel by composites aims at weight saving. The steel component is a channel type of structure made of two plates that serve as external supports of the sandwich plate. A finite element model is used to compare with the experimental results and to predict the critical regions of stress concentration. The results include load-deflection and load-strain curves with the maximum value of the shear and bending loads. The critical locations and failure loads have been investigated too. [ABSTRACT FROM AUTHOR]

This study reports a multi-scale structural analyses of a mainline floating double carcass marine hose (nominal diameter 508 mm, length 10.7 m, design pressure 2.1 MPa, weight 4100 kg). A material change in the reinforcement cords of the traditional hose is proposed, from polyester and polyamide to hybrid aramid/polyamide cords, allowing an improvement in design, reducing weight and increasing flexibility. Two models have been developed to obtain the hose responses. Firstly, a finite element model of the traditional system was built to perform a macro-scale analysis of global hydrodynamics loads in the hose line using Orcaflex™ software. Then, a non-linear finite element model was developed for meso-scale analysis using Abaqus™ software. Rubber and cords were modeled using hyperelastic models, and axial, bending and torsional stiffnesses were evaluated. Experimental tests were carried out to assess the mechanical response of an actual full-scale hose. The reduced number of layers of the hose using hybrid cords, compared to the traditional one, allowed a reduction in weight of 15%, and brought also a decrease in specific axial, torsional and bending stiffnesses of 43.9%, 52.2% and 21.6%, respectively. The multi-scale analysis predicted well the structural response of the hose line, and the reduced potential failure may increase life-time of the structure. [ABSTRACT FROM AUTHOR]

Wind and wave loadings induce stochastic bending moments in grouted connections for monopile offshore wind turbines; thus, the fatigue behavior under bending moment is extremely important. This paper presents test results on five cylindrical monopile grouted connection specimens with shear keys, which have an outer diameter of 612 mm, and different lengths of 4365 mm, 4475 mm, and 4585 mm. They were designed and tested under constant range of fatigue cyclic bending moments. The load ranges were established based on the ultimate limit state bending capacity of each specimen. It was found out that, although some local degradation exists, the whole grouted connection in the first four specimen can still survive two million load cycles with no obvious degeneracy in bending capacity. Furthermore, no obvious cracks were found at the end section of the grouted connections. Meanwhile, in the longest specimen, due to its maximum load range, the welded structures cracked after about 1.28 million load cycles indicating the end of testing. In addition, no destruction was found in the grouted connection itself. Moreover, after comparing the specimens with different lengths, the authors determined that the recommended minimum design length for grouted connections with shear keys was conservative in the commonly used design code. [ABSTRACT FROM AUTHOR]

This paper concerns the fracture assessment of a clad pipeline subjected to large bending moment, and identifies different parameters influencing the fracture behaviors. The evolution of Crack Tip Opening Displacement (CTOD) of a pipeline containing a canoe shape crack on the external surface of the girth weld is studied under pure bending and combined pure bending and internal pressure through 3D elastic-plastic Finite Element (FE) simulations. Various parameters affecting the evolution of CTOD like crack depth, crack length to perimeter diameter ratio, internal pressure and the weld geometrical configurations have been investigated. It is observed that only the average width of the weld has a significant influence on the fracture response under pure bending, while the weld reinforcement height and fusion line slope have a moderate influence on the fracture behavior under biaxial loading. The crack at the interface between the weld and back steel has a similar fracture response to that of a crack located in the weld with equivalent effective crack depth. Finally, a strain based Failure Assessment Diagram (FAD) is proposed and compared with the fracture assessments produced by BS7910:2013, and 3D elastic-plastic FE simulations suggest that the British Standard is more conservative especially for deep cracks. [ABSTRACT FROM AUTHOR]

The anchored sheet pile quay wall with a separate pile-supported platform was invented to meet the functional and serviceable requirements of engineering practice, including the higher elevation of retained soils and smaller wall deflection, based on the conventional anchored sheet pile structure. This paper presents the field testing as well as the three-dimensional numerical analysis on the first practical case of the new structure. The performance of the structure and soil is described and discussed, including the lateral deflection, bending moment, axial force, tensile force, and lateral earth pressure. The measured data and computed results show that the lateral deflection of the sheet pile wall can be significantly reduced, and the measured maximum lateral displacement is approximately 0.21% of the wall height in this case. The bending moment and axial force of the supporting piles are generally greater than those of the sheet pile and anchor wall, indicating that the pile-supported platform is efficient for reducing the loads acting on a sheet pile. The effects of the pile-supported platform can be summarized as a combination of blocking effect of the supporting piles to carry the lateral earth pressures as well as a load-relieving effect of the platform to transfer the vertical loads to deeper foundation soils through the pile. Compared to the numerical results, Coulomb's earth pressure theory significantly overestimates the earth pressure loads acting on the sheet pile at higher elevations. Furthermore, the dredging activity has greater effects on the behaviours of the sheet pile wall and front-pile than the superstructure construction. [ABSTRACT FROM AUTHOR]

Modern offshore jacket structures are designed with piles that are carrying variable axial loads, large shear forces and bending moments. Even if the geometry of the grouted connection is quite simple the load transfer mechanism is complex. It involves friction, contact stresses, brittle material, abrasion, cyclic degradation, etc. Current design recommendations were developed based on relatively small scale test and with only a few tests performed with cyclic loads that include change of load direction. In order to study the capacity of grouted connections with shear keys for alternating axial load, four (4) segment specimens were tested. The specimens were full scale representation of a segment of a part of the annulus of an axially loaded pile sleeve connection. The load-carrying axial capacity under cyclic loading was found. [ABSTRACT FROM AUTHOR]

This paper addresses collapse behaviour of Very Large Floating Structure (VLFS) under extreme vertical bending moment. The study is performed as part of risk analysis to evaluate the consequence of a rare collapse event. Elastic and plastic deformation of VLFS develops under the extreme vertical bending moment while the deformation interacts with the fluid around VLFS. Therefore, hydro-elastoplasticity analysis need be developed taking account of these effects. In this study, the whole VLFS structure is modeled as two elastic beams with an elasto-plastic hinge embedded at the connection. The structural deformation is formulated by using finite element method (FEM). The hydrodynamic behaviour is modeled by using Rankine source panel method in time domain based on two-dimensional potential theory. The two models are coupled. A series of scaled model tests is performed for validation. Simulation and tank test results for the basic collapse behaviour of VLFS are presented and discussed. The numerical method is applied further to a realistic VLFS design to clarify its collapse behaviour. [ABSTRACT FROM AUTHOR]

A systematic study was performed in laboratory model tests to assess the response of cement-improved reinforced monopiles to lateral monotonic and cyclic loading in clay. The overall load‒deflection behavior and profile of the bending moment was fully studied in monotonic tests, in addition to the p - y curves of the reinforced and unreinforced piles. Cyclic loading tests were carried out at different cyclic magnitude values and load ratios, and the cement-improved soil reinforcement range was also varied. This study provides several insights into the ongoing development of the deflection, unloading stiffness and bending moment of cement-improved soil reinforced piles as cycling progresses, which can provide empirical design recommendations for cement-improved soil reinforced monopiles subjected to lateral cyclic loading. Based on the typical p - y curve models of pile in soft clay and stiff clay, by considering the proportion of soil resistance shared by cement-improved soil and soft clay around a pile under lateral load, the modification factors of two parameters p u and y 50 are derived, and then a modified p - y curve model of cement-improved soil reinforced piles in soft clay is established. • A systematic study for the monotonic response of the cement-improved soil reinforced piles have been fully studied. • Several fresh insights into the ongoing development of deflection, unloading stiffness and bending moment of reinforced pile as cycling progresses are provided. • The modification factors of two parameters p u and y 50 are derived, and a modified p - y model of cement-improved soil reinforced pile in clay is established. [ABSTRACT FROM AUTHOR]

For offshore wind farms which are planned in sub-arctic regions like the Baltic Sea and Bohai Bay, support structure design has to account for load effects from dynamic ice-structure interaction. There is relatively high uncertainty related to dynamic ice loads as little to no load- and response data of offshore wind turbines exposed to drifting ice exists. In the present study the potential for the development of ice-induced vibrations for an offshore wind turbine on monopile foundation is experimentally investigated. The experiments aimed to reproduce at scale the interaction of an idling and operational 14 MW turbine with ice representative of 50-year return period Southern Baltic Sea conditions. A real-time hybrid test setup was used to allow the incorporation of the specific modal properties of an offshore wind turbine at the ice action point, as well as virtual wind loading. The experiments showed that all known regimes of ice-induced vibrations develop depending on the magnitude of the ice drift speed. At low speed this is intermittent crushing and at intermediate speeds is 'frequency lock-in' in the second global bending mode of the turbine. For high ice speeds continuous brittle crushing was found. A new finding is the development of an interaction regime with a strongly amplified non-harmonic first-mode response of the structure, combined with higher modes after moments of global ice failure. The regime develops between speeds where intermittent crushing and frequency lock-in in the second global bending mode develop. The development of this regime can be related to the specific modal properties of the wind turbine, for which the second and third global bending mode can be easily excited at the ice action point. Preliminary numerical simulations with a phenomenological ice model coupled to a full wind turbine model show that intermittent crushing and the new regime result in the largest bending moments for a large part of the support structure. Frequency lock-in and continuous brittle crushing result in significantly smaller bending moments throughout the structure. • Scale-model tests for offshore wind turbines interacting with sea ice were performed using a real-time hybrid test setup. • Four regimes of ice-induced vibrations for offshore wind turbines were found. • The effect of turbine operation on the development of ice-induced vibrations was found to be minor at low ice speeds. • Multi-modal interaction and intermittent crushing lead to the largest bending moments in the support structure. [ABSTRACT FROM AUTHOR]

Lattice cement soil mixing (LCSM) walls are constructed to relief the marine slope soil movement that will trigger failure of the pile-supported wharf, the structural performance and pile-soil interactions after the LCSM implementation are major concerns. This paper investigated motion modes, load-displacement relations, soil and pore pressures, and bending moments of pile-supported wharfs with LCSM walls subjected to yard load-induced slope soil movement via centrifuge modeling. Results showed that the LCSM wall tilted to compress the soil and pile, inducing the tilting of the wharf. The lateral structural displacement was effectively restricted by the LCSM wall compared with that of a nonreinforced wharf, but the LCSM wall was not superior to the other lattice wall type with legs in limiting the lateral structural displacement, and the deep LCSM wall worked better at larger soil movement. The rear piles were evidently affected by slope soil movement and were compressed in the middle part. Soil pressures generally increased with increasing yard loads, whereas their distributions were deeply affected by different LCSM wall depths. Pore pressures were greater around the tilting LCSM wall because of larger soil shear areas but dissipated when soil movement stopped. Bending moment distributions indicated evident waterside curvatures in rear piles, whereas waterside curvatures occurred in the upper part and landside curvatures occurred in the lower part in front and middle piles, the effects of LCSM wall types and depth on bending moment distributions were tremendous. • The LCSM wall effectively restricted the lateral displacement of the wharf structure, but was not superior to the FCSM wall. • The LCSM wall tilted to compress the soil and pile, inducing the tilting of the wharf. • Rear piles were evidently affected by slope soil movement and were compressed in the middle part. • Pore pressures increased in soil shearing areas but dissipated when soil movement stopped. • Bending moment distributions indicated evident waterside curvatures in rear piles. [ABSTRACT FROM AUTHOR]

The three-planar tubular Y-joint (3Y-joint) is the main part of the fatigue assessment of tripod substructures of offshore wind turbines (OWTs). As typical multiplanar tubular joints, 3Y-joints are affected a lot by multiplanar interaction between braces. Moreover, the locations of hot spot stress (HSS) can vary considerably under different load types. Thus, the distributions of stress concentration factor (SCF) and multiplanar interaction factor (MIF) along weld toe curves are necessary to calculate HSS. Considering these requirements, this study focuses on the 3Y-joint considering the wide application of the tripod substructure of OWT. A finite element (FE) analysis method is introduced and validated. Then, a numerical database is established covering common ranges of parameters used in practice. The SCF and MIF of 3Y-joint under in-plane bending moment are analyzed. Distribution formulas are proposed and proved suitable for calculating HSS in engineering design. • The database used to derive empirical formula covers common ranges of geometric parameters used in practice. • The stress concentration factor is most sensitive to θ , while the multiplanar interaction factor is most sensitive to β. • The R 2 of distribution formulas of SCF is greater than 0.99 and that of MIF is greater than 0.92. [ABSTRACT FROM AUTHOR]

Ships avoid severe sea states for the safety of lives and property and to save energy. Therefore, the actual sea states encountered by ships differ from nature and are affected by human operational effects that we refer to as the "ship operational effect". The evaluation of the ship operational effect is crucial for the rational design of structural strength of the hull. In this study, we derived the sea states encountered over 25 years in the North Atlantic, by considering storm avoidance by merchant ships. We then performed long-term predictions of the ship motions and wave loads of 75 merchant ships. Existing pioneering studies used automatic identification system (AIS)-based ship locations and timestamps to subsample wave hindcast data along ship tracks for a limited duration. Unlike existing studies, we used a statistical storm avoidance model of merchant ships to reconstruct the sea states, encountered over 25 years, in the North Atlantic. Owing to the ship operational effect, the long-term prediction values of roll motion, pitch motion, vertical bending moment amidships, and hydrodynamic pressure on bottom centerline amidships of merchant ships, at the probability level 10−8, were reduced by approximately 10–20%, and the coefficient of the ship operational effect was 0.8–0.9. Furthermore, we evaluated the uncertainties in the ship operational effect. The values deviated by as much as 6%, depending on the choice of wave hindcast products (TodaiWW3-NK, IOWAGA, and ERA5). The variation based on the parameter settings of the storm avoidance model (severity of the storm, radius of influence of the storm, and number of ship locations) was up to approximately 1 m at a probability level of 10−5 of the encountered sea states for 25 years. • Evaluation of ship operational effect is carried out considering encountered sea states for the design lifetime of ships in North Atlantic. • Long-term prediction of ship motions and wave loads at 10−8 were reduced by about 10∼20% due to ship operational effect. • Uncertainties related to ship operational effect were discussed in terms of the hindcasts, ship lengths, and parameters setting of the storm avoidance model. [ABSTRACT FROM AUTHOR]

Box-shaped damage affected volumes are applied, with parametric variation of their positions and extensions, to an otherwise intact shuttle tanker in full load condition. The vessel's deadweight is numerically calculated and the lightweight is estimated using semi-empirical formulations to a great extent. For each damage configuration, the final position attained by the ship is investigated and the corresponding global loads are assessed, in terms of still water vertical bending moment and shear force. The ship is considered to be floating in the absence of waves and a quasi-static version of a generalized adaptive mesh pressure integration technique code, for progressive flooding of floating objects, is used to model the progression of the floodwater and the vessel's attitude. The probabilistic model suggested by the Marine Environment Protection Committee of the International Maritime Organization (MEPC-IMO) is considered for the collision induced probabilistic distribution of the damage boxes. A total of 90 damage cases are considered and comparisons of the maximum loads and the location where these take place is carried out relative to the intact case. The minimum design values for still water bending moment and shear force, included in the Common Structural Rules for Bulk Carriers and Tankers of the International Association of Classification Societies (IACS), are introduced in the analysis and their envelopes are compared with the numerically obtained values in light of a probabilistic assessment. Several conclusions are taken regarding the effects of the damage parameters variation, and important findings are presented specifically when accounting for the MEPC-IMO probabilistic distribution, in opposition to a uniform distribution of the damage cases. [ABSTRACT FROM AUTHOR]

Hull girder ultimate strength is an essential parameter for the ship's structural design. Numerous research studies have been done about hull girder bending. However, few experimental tests have been carried out due to the fabrication cost, the difficulty of monitoring loads, and mapping surfaces of models on large- and medium-scale. This paper conducted a four-point bending test of a small-scale hull box girder. The dimensions of the box girder model are defined from geometric slenderness ratios representing a double bottom panel at the midship of a typical Suezmax tanker. Numerical finite element models are developed, where the friction coefficient between the model and its supports is determined based on experimental correlation. The numerical models with different initial imperfection distributions are considered to perform ultimate strength analyses. Initial imperfections implemented in the models are based on least-squares regression of the geometric imperfections measured from the experimental models. Strain gauges were installed at the upper panel and obtained measurements compared with local numerical strains. Both experimental and numerical models showed that the upper panel of the box girder presented initial structural failure in the plating between stiffeners, which evolved to the stiffeners, following the expected buckling sequence of a reinforced panel. IACS formulation and direct methods have been employed to evaluate the ultimate bending moment. A correlation between the theoretical and experimental results indicates that the IACS formulation better predicts the ultimate bending moment, with the additional advantage of estimating the curvature. This paper also provides methodology and parameters for future studies of the ultimate strength of ship panels with different slenderness ratios. • Ship ultimate longitudinal strength based on box girder modeling. • Laboratory test of small-scale box girder using four-point bending. • Numerical and experimental correlation for different initial imperfection distributions. • Box girder bending strength, including IACS formulation. [ABSTRACT FROM AUTHOR]

Previous investigations have shown that water-pier interaction has a considerable effect on the seismic response of bridge piers in deep water. However, most of those studies assumed that the foundation is rigid and there are few studies on the hydrodynamic effects on the piers considering soil-structure interaction under earthquakes. To investigate the hydrodynamic effects on bridge piers built on soft ground, series of centrifuge shaking table tests were conducted. In the tests, a pile foundation bridge pier was scaled down by a factor of 1:50. The height of the pier was 340 mm, and the length of the pile was 200 mm. The pile foundation pier was installed in soft soil contained in a laminar shear box. Three depths of water, i.e., no water, 150 mm and 300 mm, were considered. The dynamic responses of pier displacement, acceleration and bending moment of the pier and piles, hydrodynamic pressure on the pier, soil pressure on the pile and pore-water pressure in the soil were measured. The results show that the natural frequency of the pier decreases as the water depth increases, and the displacement of the pier with a water depth of 300mm is significantly reduced in comparison with that of no water. However, water increases the acceleration and bending moment of the pier and the pile. The results also show that as the water depth increases, the hydrodynamic pressure acting on the pier and the dynamic soil pressure exerted on the pile both increase under earthquakes. • Seismic dynamic tests of a pile foundation bridge pier in soft soil considering water-pier interaction using centrifuge shaking table were conducted. • Three water depths, i.e., no water, low water and high water, were considered. • The effects of hydrodynamic pressure on the seismic response of a pile foundation bridge pier considering pile-soil interaction were explored. • The influence law of hydrodynamic pressure on the pier under different water depths was revealed. The influence of dynamic soil pressure on the pile under different water depths under earthquakes was revealed. [ABSTRACT FROM AUTHOR]

The historic canal wall structures in many Northern European cities have been built as masonry walls on a timber deck founded on timber piles. For analysis of the resistance of those structures and assessment of their remaining service life, suitable and accurate calculation models are needed. Thereto an analytical method was developed for modelling laterally loaded pile groups in layered sloping soil. In the proposed method, the bending of a pile, which is subjected to a lateral load and axial load , is described by a beam on a Winkler elastic foundation in which the soil behaviour is represented by a series of independent p-y springs, idealized with a bilinear elastic-perfect-plastic approximation. The plastic limit was computed with Brinch Hansen ultimate soil resistance and the elastic soil response by the Ménard stiffness. The plastic limit was corrected for each depth, based on the reduction of the passive soil wedge due to pile group effects and the presence of a sloping surface. The analytical model was calibrated and validated with three field experiments, one full-scale lateral load test of a 3 × 5 pile group in soft clays and silts (Snyder, 2004), one full scale lateral load test of a single pile located on a slope in layered soils (Mirzoyan, 2007) and one small scale lateral load test of a single pile located near a slope in sand (Abdelhalim et al., 2020). The proposed method can adequately predict bending moment distributions and pile deflections and in addition, a good consistency between the analytical model and experimental tests was observed. The method is very fast, making it suitable for probabilistic, Monte Carlo type, simulations and reliability updating to determine the probability of failure of quay walls or other structures with horizontally loaded piles. • Analytical model describing lateral loaded piles in sloping layered soil is developed. • Pile group and slope effects are based on a new passive wedge interaction method. • The model allows fast computation making it suitable for probabilistic analysis. • With relatively little input, a proper estimate of the pile behaviour can be made. [ABSTRACT FROM AUTHOR]

Almost all the researchers devoted themselves to the ultimate strength of ship girder in static method previously. Ships sailing in the waves are always in motion, so that the hull structures are subjected to dynamic loads such as dynamic wave bending moment and slamming loads and generate dynamic response. The ultimate strength of structures under dynamic loads can reflect the safety level of ships more truly. Based on the Idealized Structural Unit Method (ISUM) and the solution method of dynamic equation, this paper develops the ISUM and applies it to the analysis of dynamic ultimate strength of stiffened plate. The accuracy and efficiency of ISUM are verified by comparing the calculation results with FEM, and the difference characteristics of structural strength under dynamic and static loads are analyzed. The influences of strain rate effect, damping and loading period on the ultimate strength of stiffened plate are discussed. This analysis is of reference significance for the safety and reliability design of ship structure. • Dynamic solution is derived and program is developed based on the Idealized Structural Unit Method (ISUM). • Dynamic analysis considering the strain rate effect, dynamic yield stress and damping effect is conducted to obtain the dynamic collapse behavior of typical stiffened plate. • Dynamic ultimate load is related to the structures and dynamic load parameters. The obvious strain rate effect and inertia effect can be observed with shorter load period and/or higher frequency. [ABSTRACT FROM AUTHOR]

When technically specifying ships for the future, the following aspects are examples of what we will have even more focus on than today: bigger, lighter, and faster. Thereby, the hydroelastic type of structural response will be more and more significant. Furthermore, it is well-known that the whipping-induced stresses are having a higher frequency than the ordinary wave-induced stresses; hence, some doubts are cast on the probability that the dynamic effects may provide additional strength reserves. Therefore, this research aims to analyze the dynamic ultimate capacity of ultra-large container ships under realistic loading scenarios. The hull-girder is subjected to a combined bending moment, resulting from a long-term hydroelastic analysis, with the lateral loads and to local loads given by different cargo loading cases. The numerical results are discussed, and the dynamic load factors are derived as the ratio between the dynamic capacity and the quasi-static one. Finally, it is shown that the strain rate effect is negligible in the analysis of the ultimate strength of ship structures subjected to whipping-induced stresses. • an extensive investigation of the dynamic ultimate strength is performed using state-of-the-art finite element analyses to investigate the influence of the dynamic effects induced by slamming-induced whipping over the structural capacity of a large container ship. • The effect of three different loading conditions: pure bending, full load, and one-bay empty, is investigated and summarized; for each condition, the dynamic load factors are computed as the ratio between the dynamic capacity and the quasi-static one are derived. • The detailed procedure and definition of the dynamic ultimate strength analysis is documented, including valuable discussion on the limitation of the available strain-rate sensitivity constitutive models. [ABSTRACT FROM AUTHOR]

Present article proposes improved assessment of the ultimate bending capacity (ultimate bending moment), i.e. enhancement of the ultimate limit state evaluation in the concept design of the monotonous thin-walled structures predominantly subjected to vertical bending loads during their exploitation. An alternative progressive collapse analysis method is proposed, which incorporates direct consideration of various relevant distributed load effects and consequently enables more sophisticated evaluation of the ultimate bending capacity and more accurate and reliable identification of the critical cross section and its collapse sequence. Relevant aspects of the employed approximate model for the cross sectional warping due to vertical bending are considered and determination of the (longitudinal) warping displacements and strains, shear strains and stresses, as well as the corrected longitudinal strains is described. Influence of the (ultimate) shear capacity on the (ultimate) bending capacity is discussed and detailed description and critical overview of the proposed method is given. Finally, various aspects of the considered problem and accuracy of the proposed approach are discussed and demonstrated on example of the thin-walled box-girder, whereby detailed comparison of the results obtained by the proposed approach and nonlinear finite element method analyses is given. [ABSTRACT FROM AUTHOR]

The paper focuses on time-variant longitudinal strength of bulk carriers under corrosion wastage, applying both Taylor series expansion method and Monte Carlo simulation. Hull girder section modulus and ultimate bending moment capacity are determined, by classical beam theory and the commonly applied incremental-iterative approach, respectively. Two main aspects are fully discussed and investigated, according to the final recommendations of last ISSC Report. The former regards the covariance between annual corrosion rates of individual structural members, commonly assumed as uncorrelated. Really, as it is conceivable that a certain correlation exists, three different cases are investigated: uncorrelated variables, fully correlated variables, full correlation between structural members belonging to the same category of compartments. The latter investigates the probability density function of both hull girder section modulus and ultimate bending capacity, because the Central Limit Theorem cannot be applied when correlation among random variables exists. Finally, as a test example, the bulk carrier section, presented in the last ISSC benchmark study, is analysed. [ABSTRACT FROM AUTHOR]

Abstract: An experimental study is presented of three box girders made of mild steel subjected to pure bending moment, with different spacing between frames. The moment curvature curves are presented, allowing for the analysis of elastic–plastic behaviour until collapse and the evaluation of the ultimate bending moment and post collapse behaviour for each experiment. The residual stress relief during loading and unloading path is also analysed. The effect of the span between transverse frames on the ultimate bending moment of the box girder is studied and thus its dependence on the column slenderness of the panel under compression can be established. The energy dissipated by internal friction during each load cycle is evaluated and compared with elastic potential energy. [Copyright &y& Elsevier]

Abstract: This paper describes full-scale measurements of the wave-induced vertical bending moment amidships a 9400 TEU container carrier and focuses on the effect of the hydro-elastic high-frequency vibration on the extreme hogging wave bending moment. One extreme event, where the vertical wave-induced hogging bending moment amidships slightly exceeds the design value, is analysed and the measurements are verified by the use of the relationship between measurements of accelerations and strains and simple beam theory. The measurements are found to be reliable. In the extreme case, the high-frequency vibrations caused by impulsive loads are observed to be of the same magnitude as the rigid-body wave-induced response and thus acts to double the total vertical bending moment amidships. It was also found that even though the ship is sailing in bow quartering seas, only the 2-node vertical vibration mode is apparently excited. Following the extreme event analysis and verification, three hours of strain measurements are used for establishing a Gumbel distribution for the extreme value prediction, and it is found that the probability of exceeding the rule design wave bending moment by 50% in the given sea state is quite significant. Finally, the hydro-elastic behaviour of the hull girder is assessed by simple approximations using the measured statistical properties and closed-form expressions and the agreement with the actual measurements is found to be good. [Copyright &y& Elsevier]

Abstract: In this study, we propose a numerical procedure to analyze floating plate structures with multiple hinge connections in regular waves and investigate the maximum bending moment and deflection in the plate structures. The directly coupled equations of motion for the hydroelastic analysis are discretized by the boundary element method for fluid and the finite element method for plates. The hinge connection is modeled by releasing the rotational degrees of freedom of the plate finite elements, in which a complete condensation procedure is used considering structural mass and stiffness and fluid-structure interaction terms. Wave tank experiments have been performed to verify the numerical results. The modeling capability of the proposed numerical procedure is demonstrated through floating plate problems with 1- and 2-directional multiple hinge connections. The numerical analyses show the effect of the number of hinge connections used on the maximum bending moment and deflection of the floating plate structures according to the aspect ratio, bending stiffness and incident wavelength. [Copyright &y& Elsevier]

Abstract: Vertical bending moment (VBM) is of crucial importance in ensuring the survival of vessels in rough seas. With regard to conventional vessels, wave-induced maximum VBM is normally considered to be experienced in head seas. It is conservative to determine the extreme VBM based on either numerical simulations or model tests in long-crested head seas. Extensive model tests have been conducted in head seas with focus on the nonlinear vertical responses in severe seas, and the measured results were compared with numerical calculations for validation. Unexpected phenomena, however, were observed during the model tests of an ultra-large containership. The maximum sagging and hogging VBMs were encountered in oblique seas. Furthermore, the significant wave height used in oblique seas was even smaller than that used in head seas. The nonlinear vertical load effects in oblique seas require further investigations for this particular vessel. Limited experimental results in oblique seas have been reported, in which the lateral responses were always more concerned than the vertical responses. Up to now, rare systematic comparisons of the nonlinear vertical responses between head and oblique seas have been published, especially when the hydroelastic effects are also accounted for. A 13000-TEU ultra-large containership model, which was designed by Hyundai Heavy Industries (HHI), has been tested in the towing tank and the ocean basin at the Marintek center in Trondheim. The experimental results in regular waves are first compared between head and oblique seas. The statistical characteristics of the VBM amidships under nineteen irregular wave conditions are then investigated. Next, the extreme hogging and sagging VBMs are compared under different wave conditions with focus on the extreme hogging VBMs. At the end of the paper, the uncertainties in the experiments are discussed. [Copyright &y& Elsevier]

Abstract: The deformation of boat hull bottom panels during the initial phase of slamming is studied analytically using a linear elastic Euler–Bernoulli beam as a representation of the cross section of a bottom panel. The slamming pressure is modeled as a high-intensity peak followed by a lower constant pressure, traveling at constant speed along the beam. The problem is solved using a Fourier sine integral transformation in space and a Laplace–Carson integral transformation in time. Deflection and bending moment as functions of time and position for different speeds, bending stiffnesses, etc. are given. In particular the effect of slamming load traveling speed on structural response of the simplified bottom structure is investigated. It is found that rather large deflections and bending moments are encountered at certain speeds of the pressure, which suggests that bottom panels may benefit from tailoring their stiffness and mass properties such that loads are reduced. This would vary with boat particulars and operation (deadrise angle, mass, speed, sea state, etc). The importance of the high-intensity pressure peak often encountered during slamming is also studied. It is seen that for relatively slow moving slamming loads the pressure peak has little influence. However, for faster moving loads its influence can be significant. [Copyright &y& Elsevier]