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F. Besseling

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Evaluation of performance of analytical and numerical methods to account for liquefaction effects on the seismic response of anchored quay walls

Conference paper (2017) - W.A. van Elsäcker, F. Besseling, H.J. Lengkeek, R.B.J. Brinkgreve, R.B.J. Brinkgreve, J.G. de Gijt, Sebastiaan N. Jonkman

Liquefaction induced by earthquakes has shown to have potential devastating influence on seismic performance of anchored quay walls. Therefore, measures to mitigate liquefaction are commonly part of the design of quay walls in
seismically active regions. Such mitigation measures are costly. Moreover, these measures are difficult to implement for existing structures in operation. For these reasons, proper tools that can accurately predict the effects of liquefaction on anchored quay walls are valuable for engineering purposes. Numerical tools like finite element analysis can potentially replace simplified code based methods, such as the Mononobe-Okabe method. However, performance of numerical models that account for liquefaction and pore pressure accumulation is crucial towards the use of numerical tools for this purpose. Initial stress states influence both the liquefaction resistance of the soil as well as the performance of the constitutive model. This study proposed a new calibration procedure in order to deal with the influence of static shear and overburden stress in the model. Zones around the structure with specific corresponding stress states are defined for which the stress state dependent constitutive model behaviour is calibrated based on laboratory results and literature.This study evaluates the performance of finite element calculations with the UBC3D-PLM soil constitutive
model based on a reported case study of two quay walls in Akita Port, Japan for the 1983 Nihonkai Chubu earthquake. It also evaluates to what extent Mononobe-Okabe calculations with code-based corrections for liquefaction effects could reproduce the observed performance of the Akita Port quay walls. The results shown by the analysis employing the new developed calibration procedure indicate good correspondence with observations in the field. On the other hand, Mononobe-Okabe methods including corrections for liquefaction effects give a poor fit to the observed behaviour. The response indicates that dynamic analysis with the UBC3D-PLM model using the proposed calibration procedure is capable to give insight in effects of excess pore pressures on the seismic performance of an anchored quay wall. This study mainly only focussed on liquefaction triggering as a function of stress state and the post-liquefaction stress-strain behaviour predicted by UBC3D-PLM was only evaluated at a basic level.@en

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Influence of temperature on natural vibrations of steel bridges

Master thesis (2020) - C.N. Kortendijk, A. Metrikine, E. Lourens, F. Besseling, C Jolink, C. Kasbergen

Response of an Offshore Wind Turbine supported by a Non-Local Winkler Foundation

An Efficient 1D Time-Domain Model accounting for the 3D Frequency-Dependent Dynamic Soil Stiffness

Master thesis (2019) - Y.S. Hasper, A. Metrikine, K.N. van Dalen, F. Besseling, J.S. Hoving, Pim Versteijlen

With increasing evidence of human-induced accelerated climate change, the need of sustainable, non-polluting, energy sources becomes evident. Offshore wind generated electricity is currently one of the most promising sources of energy to create a sustainable global energy mix. The offshore wind industry has developed rapidly over the last years. The cumulative installed capacity shows an exponential growth. Monopiles remain the most popular substructure type of all installed substructures in Europe. This thesis focuses on calculation methods to evaluate the response of that foundation type.

The interaction between a monopile and soil is called soil-structure interaction (SSI). In the offshore wind industry, SSI is commonly modelled as a 1D local Winkler foundation with local nonlinear elastic springs to represent the lateral soil stiffness. The stiffness is often based on semi-empirical relations between the lateral displacement of the pile and the soil pressure (p-y method). This approach neglects the interaction effects between different soil layers and there are uncertainties regarding the validity of applying this method to large diameter, rigidly behaving, monopiles.

In this thesis, a 3D linear-elastic (LE) finite element (FE) model is used to compute 1D global (non-local) complex-valued dynamic soil stiffness, which captures the coupled 3D reactions of soil to the pile. The frequency dependence of local and non-local linear-elastic lateral, rotational and coupling dynamic soil stiffness is analysed for heterogeneous soil stratigraphy. The effect of different boundary conditions in the 3D model formulation to the frequency dependence of dynamic soil stiffness is analysed.

The complex-valued-frequency dependent dynamic soil stiffness kernels are approximated by frequency independent coefficient matrices for added mass, damping and stiffness. The performance of the coefficient matrices in terms of representing the complex-valued dynamic soil stiffness is analysed with cost functions. It was found that the dynamic soil stiffness can be approximated by frequency independent added mass, stiffness and damping coefficient matrices in the frequency range of interest for offshore wind.

A 1D Timoshenko beam model is developed in the frequency-domain and is discretised in space by Euler’s central finite difference method. The added mass, stiffness and damping matrices, which represent the non-local Winkler foundation, are incorporated in the model. The SSI response of the 1D model to the dynamic loading is compared with the response of the 3D LE FE model in the frequency domain.

As a last step, a superstructure and turbine are integrated with the monopile SSI model and the total integrated model is transferred to the time domain. Time domain computations are performed for free vibrations, harmonic loading and realistic aero-/hydrodynamic loading scenarios. The transformation into the time domain is important since it allows the user to incorporated nonlinear wave and wind loading and air-turbine interaction effects that are considered to have a major impact on the resulting dynamic system response. The developed time-domain model is computationally very efficient in predicting the time-domain SSI response of an offshore wind turbine for varying loading scenarios.