Piles and suction caissons are the most common foundation solutions for fixed Offshore Wind Turbines at intermediate water depths. They are generally used as a single element, presenting large ...diameters and short aspect ratios. These specific dimensions drastically differ from the ones of classical applications (offshore platforms, bridges, tall buildings etc.). Thus, in this paper the validity of their modelling as beam elements for the particular problem of OWT is revised. The results of a soil-beam model, based on the integral Reciprocity Theorem in Elastodynamics and specific Green’s functions for the layered half-space for the soil behaviour coupled with Timoshenko’s beam Finite Elements, are benchmarked against the ones of a soil-shell model, based on Boundary Elements for the soil coupled with shell Finite Elements. The comparative study is conducted in terms of foundation characterization variables (impedance functions and kinematic interaction factors). Their influence on the OWT seismic response is also studied through a substructuring procedure. From the results, some expressions for determining the applicability range of the beam simplification are proposed as functions of the relative foundation-soil stiffness ratio. It is observed that this applicability range goes beyond that the one commonly considered. .
Abstract In the last few years, offshore wind energy has been increasing significantly, being the energetic potential of this technology much higher than that of other renewables energies. Most of ...Offshore Wind Turbines (OWTs) installed in Europe are founded to the sea floor but, due to the increase in offshore wind turbine installations and the visual impact problem, new locations are being considered with greater depths and increasing seismic risk. In this field, jackets substructures are one of the most attractive options. Despite the low natural frequencies that characterise these systems, the effect of the kinematic interaction can be highly relevant in OWTs on monopiles. For this reason, the need arises to analyse the importance of the influence of kinematic interaction on the seismic responses of multi-supported substructures, such as jackets with deep foundations. This paper presents a comparison of the kinematic interaction effects on the seismic response of two types of substructures for OWTs. OpenFAST is used to analyse the dynamic behaviour of OWTs founded either on monopiles or through jacket substructures on deep foundations, taking soil-structure interaction into account. The comparative study shows that the influence of kinematic interaction in both cases is notably different. As expected, in the case of the monopile, the rotational motion has a strong effect on the accelerations and the internal forces in the structure, although the impact of the translational filtered signal is small. However, in the jacket, the influence of the rotational motion is less pronounced.
The potential use of pile barriers as a ground vibration mitigation measure is analysed through an efficient numerical model. The soil is modelled as an elastic half space, using the reciprocity ...theorem and specific Green’s functions for the layered half space, while the piles are treated as beam elements. After benchmarking the proposed model against a Boundary Element model, it is used to study this type of barrier, with particular focus on how the presence of a rigid bedrock alters its performance. A significantly different behaviour when compared to the case of the half space is found if the piles reach the rigid stratum, increasing the barrier performance around the layer second natural frequency.
Summary
This paper presents a wide parametric study aimed at elucidating the influence, on the computed seismic response of bridge piers, of two related aspects of the model: (1) the adoption of the ...classical hysteretic or the causal Biot's damping models for the soil and (2) the use of two different lumped parameter models of different complexity and accuracy to approximate the impedances of the pile foundation. A total of 2072 cases, including different superstructures, pile foundations, soil deposits, and seismic input signals, are studied. The results are presented so that the influence of the different parameters involved in the analysis can be assessed. From an engineering point of view, both lumped parameter models provide, in general, sufficiently low errors. The choice of the most adequate model for each case will depend not only on the configuration of the structure and the soil‐foundation system but also on the assumed soil damping model, whose influence on the computed seismic responses is relevant in many cases. The nonphysical behaviour provided by the classical hysteretic damping model for the soil at zero frequency generates issues in the process of fitting the impedance functions. It is also found that larger deck displacements are predicted by Biot's model due to the higher damping at low frequencies provided by the classical hysteretic damping model.
•Reductions in the ductility demand of RC piers by using inclined pile foundations.•Reductions in the input seismic energy to the system due to FIM peculiarities.•Displacement-based design ...methodologies requires a strategy to account for the SSI.•Takeda’s model is used to represent the non-linear response of the plastic hinges.•Good estimations of yielding energies and ductilities are obtained with simple rules.
This paper studies the effects of the use of inclined pile foundations on the seismic response of bridges, and shows that this type of foundation is able to promote significant reductions in the ductility demand of reinforced concrete piers. To this end, a set of nine multi-span roadway viaducts with different pier heights and span lengths is defined. Each configuration is designed and dimensioned in detail following a displacement-based approach, considering both linear and non-linear expected behaviours and assuming different target ductilities for piers. The systems are assumed to be founded on a specific soil profile, and suitable pile foundation layouts and dimensions are determined for each case, with four different pile rake angles (including the vertical case) in each configuration. Soil-structure interaction phenomena are incorporated through the corresponding frequency-dependent impedance functions and kinematic interaction factors. The transverse response of the viaducts, subject to a set of seven suitable scaled real accelerograms, is computed and analysed making use of a substructuring approach and non-linear time-domain analysis in which a lumped parameter model is adopted to represent the foundation response. Results, presented not only in terms of ductility demand but also of energy dissipated in the structural system by damping or by yielding, suggest that inclined piles are clearly beneficial to the seismic response of bridges, contributing to significant reductions in ductility demand due to the particular kinematic seismic response of this type of foundations and associated reductions in the input seismic energy to the system.
This work studies the structure-soil-structure interaction (SSSI) effects on the dynamic response of nearby piled structures under obliquely incident shear waves. For this purpose, a ...three-dimensional, frequency-domain, coupled boundary element – finite element (BEM–FEM) model is used to analyse the response of a configuration of three buildings aligned parallel to the horizontal component of the wave propagation direction. The SSSI effects are studied in terms of the maximum shear force at the base of the structures in both frequency- and time-domains. The results are presented in a set of graphs so that the magnitude of the interaction effects in configurations of buildings with similar vibration properties depending on the distance between them and the angle of incidence can be easily estimated. These results show a high influence of the wave type and angle of incidence on the interaction effects, not always corresponding the worst-case scenario with the commonly assumed hypothesis of vertical incidence. It is found that for configurations of non-slender structures, the SSSI effects can significantly amplify or reduce the single building maximum response depending on the separation between structures and excitation.
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•The response of groups of piled buildings to obliquely incident S-waves is studied.•The interaction effects are quantified in terms of the structural maximum shear force.•Maximum efforts can increase up to 20% due to the presence of near constructions.•Interaction is mainly observed among buildings with similar vibration properties.•Vertical incidence hypothesis does not always correspond to the worst-case situation.
The paper presents a Winkler‐based numerical model for the analysis of the dynamic response of caisson foundations. The model allows the evaluation of the impedance functions and of the foundation ...input motion (FIM), which can be used in the framework of the substructure approach to compute inertial soil‐foundation superstructure interaction analyses. In addition, kinematic stress resultants due to seismic shear waves propagating into the soil can be estimated. The caisson is modelled as a Timoshenko beam and the soil‐caisson interaction forces are derived from the analyses of the plane‐strain vibration problem of an annular rigid ring embedded into the soil. The problem solution is obtained in the frequency domain exploiting the finite element approach and generic soil stratigraphies can be considered in the applications. The model, which is characterised by a very low computational effort, is validated by performing a parametric investigation, comparing results with those obtained from more rigorous BEM‐FEM models of the soil‐caissons systems. Finally, some applications to real caisson foundations of offshore wind turbines (OWTs) are shown to demonstrate the model accuracy in capturing the seismic response of the foundations obtained from more rigorous models.
Many international standards highlight the relevance of studying the compatibility of forces and displacements between the structure and the foundation that supports it. In the case of pile ...foundations, some authors use continuum models that rigorously reproduce the interaction of the pile with the surrounding soil. However, their high computational cost justifies the use of simplified methodologies that allow obtaining sufficiently accurate results in significantly less time. This work presents a surrogate model based on Artificial Neural Networks (ANNs) trained from a synthetic dataset generated by a continuum numerical model. A good regression capacity is observed by the proposed model, also requiring very short evaluation times. Two use examples are presented to illustrate the smooth behaviour of the ANNs model and its ability to determine the critical pile length. This surrogate model allows introducing soil–structure interaction in problems with large volume of evaluations in a feasible way without significantly compromising the confidence of the results.
•An ANN-based model can reproduce the pile stiffness in a non-homogeneous soil.•The proposed model agrees with analytical expressions present in the literature.•Active length of the pile is adequately reproduced by the surrogate model.
Purpose
Impedance data obtained by electrochemical impedance spectroscopy (EIS) are fitted to a relevant electrical equivalent circuit to evaluate parameters directly related to the resistance and ...the durability of metal–coating systems. The purpose of this study is to present a novel and more efficient computational strategy for the modelling of EIS measurements using the Differential Evolution paradigm.
Design/methodology/approach
An alternative method to non-linear regression algorithms for the analysis of measured data in terms of equivalent circuit parameters is provided by evolutionary algorithms, particularly the Differential Evolution (DE) algorithms (standard DE and a representative of the self-adaptive DE paradigm were used).
Findings
The results obtained with DE algorithms were compared with those yielding from commercial fitting software, achieving a more accurate solution, and a better parameter identification, in all the cases treated. Further, an enhanced fitting power for the modelling of metal–coating systems was obtained.
Originality/value
The great potential of the developed tool has been demonstrated in the analysis of the evolution of EIS spectra due to progressive degradation of metal–coating systems. Open codes of the different differential algorithms used are included, and also, examples tackled in the document are open. It allows the complete use, or improvement, of the developed tool by researchers.
This paper presents a three–dimensional linear numerical model for the dynamic and seismic analysis of pile-supported structures that allows to represent simultaneously the structures, pile ...foundations, soil profile and incident seismic waves and that, therefore, takes directly into account structure–pile–soil interaction. The use of advanced Green’s functions to model the dynamic behaviour of layered soils, not only leads to a very compact representation of the problem and a simplification in the preparation of the data files (no meshes are needed for the soil), but also allows to take into account arbitrarily complex soil profiles and problems with large numbers of elements. The seismic excitation is implemented as incident planar body waves (P or S) propagating through the layered soil from an infinitely–distant source and impinging on the site with any generic angle of incidence. The response of the system is evaluated in the frequency domain, and seismic results in time domain are then obtained using the frequency–domain method through the use of the Fast Fourier Transform. An application example using a pile-supported structure is presented in order to illustrate the capabilities of the model. Piles and columns are modelled through Timoshenko beam elements, and slabs, pile caps and shear walls are modelled using shell finite elements, so that the real flexibility of all elements can be rigorously taken into account. This example is also used to explore the influence of soil profile and angle of incidence on different variables of interest in earthquake engineering.
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