This paper presents the development and testing of a lab-scale Gentle Driving of Piles (GDP) shaker. Conventional impact piling for offshore monopile installation faces challenges due to noise regulations and its adverse marine environmental impacts. The GDP method, which integrates high-frequency torsional vibrations with low-frequency axial vibrations, aims to mitigate these issues. In this work, a new GDP shaker is designed and tested to enhance vibratory pile driving by independently controlling torsional and vertical vibration amplitudes and frequencies. Laboratory tests were conducted using the newly designed shaker for pile driving in sandy soil to evaluate its performance. The results indicate a significant reduction in power consumption and improved pile drivability with high-frequency, low-amplitude torsional vibrations. This study highlights the importance of optimizing dynamic inputs for enhanced pile penetration and reduced environmental impact, showcasing the potential of the GDP method as a promising alternative to traditional impact piling techniques.

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The reliable design of high-rise buildings subject to wind-induced vibrations is important for ensuring comfort and safety. However, the Eurocode recommendations and common design practices used to estimate natural frequency and damping parameters in the design stage have been found to be inaccurate, leading to unreliable predictions of building accelerations. Previous studies have shown that soil-structure interaction (SSI) can have a significant influence on these parameters, especially for high-rise buildings on soft soils. This study presents a formulation of a simple model to include soil-structure interaction effects in the natural frequency and damping parameters. It also demonstrates the compatibility of this model with the current Eurocode procedures. The study compares the results of the simple SSI model with those of a continuous model of the New Orleans tower under design wind loading. In previous work, this continuous model was validated against in-situ measurements on the New Orleans tower. The results demonstrate that the simple SSI model significantly improves the accuracy of the predicted building accelerations under wind loading for the New Orleans tower, compared to accelerations determined in the original design and accelerations computed with the Eurocode guidelines.@en

This paper presents a new shaker design for the Gentle Driving of Piles method. Specifically, a lab-scale vibratory device has been developed that can simultaneously apply axial and torsional vibrations, both possessing frequency-amplitude decoupling. This design was implemented and tested in a lab-scale experimental campaign, where both pile and soil were extensively instrumented. The monitoring of the dynamic pile and soil behaviours during driving with various installation settings is of utmost importance to comprehend the governing mechanisms of the process. In that manner, the optimization of pile installation may be realized both for axial vibratory driving and GDP. In this work, the frequency-amplitude decoupling is pivotal, as it is showcased that both enhanced installation performance and reduced power consumption can be attained with proper selection of the installation settings and exploitation of high-frequency torsion.

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For offshore wind turbines (OWTs), the monopile comprises the most common type of foundation and vibratory driving is one of the main techniques for monopile installation (and decommissioning). In practice, prior to pile installation, a pile driving analysis is performed to select the appropriate installation device and the relevant settings. However, pile penetration results from a complicated vibrator-pile-soil interaction and better understanding of the latter is necessary for an efficient installation process. During the course of installation, the interface and boundary conditions of the pile continuously alter due to the soil layering and the non-linearity of the soil reaction. In this paper, a set of experimental data from an onshore experimental campaign are employed in a numerical scheme to identify the pile strain field based on in vacuo modes of simpler yet related systems. By mapping the pile strain field onto physically-based shape functions, the evolution of the soil reaction during pile installation can be studied, in order to facilitate the back-analysis of driving records and, by extension, improve pile drivability and vibro-acoustics predictions.

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Gentle Driving of Piles (GDP) is a new technology for the vibratory installation of tubular (mono)piles. Its founding principle is that both efficient installation and low noise emission can be achieved by applying to the pile a combination of axial and torsional vibrations. Preliminary development and demonstration of the proposed technology are the main objectives of the GDP research programme. To this end, onshore medium-scale tests in sand have been performed on piles installed using both impact and vibratory driving methods (including GDP). After presenting the development of a purpose-built GDP driving device and the geotechnical characterisation of the site, this paper covers the execution of GDP installation tests. Focus is on the installation performance of GDP-driven piles, which is discussed with the aid of structural and ground monitoring data. The comparison between piling data associated with GDP and standard axial vibro-driving points out the potential of the proposed installation technology, particularly with regard to the beneficial effect of the torsional vibration component. The findings of this study encourage further development of the GDP method and its future extension to offshore full-scale conditions.

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In this paper, the energy flux in a pile modeled as an elastic shell, is studied theoretically and experimentally. Based on this analysis, a new procedure is proposed to quantify the pile installation efficiency. This procedure is of importance for vibratory installation of the foundations of offshore wind turbines and it is believed to be the first procedure that relies directly on the energy propagating down the pile rather than the energy supplied by the vibratory shaker. The proposed approach is tested on piles installed by two distinct vibratory techniques, i.e. the axial vibratory driving and the recently developed Gentle Driving of Pile (GDP) method. The field data obtained during an experimental campaign were analyzed with the proposed energy flux approach. The cumulative energy flux in the pile normalized by the energy input of the shaker is found to be the best measure for quantification of the installation efficiency. Correspondingly, the main proposition of this paper is that the installation efficiency will be maximized provided that the normalized cumulative energy flux is at its maximum.

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The focus of this study is to characterize delamination using static and dynamic tests and to assess the interface failure mechanism of an innovative hybrid concrete beam, made out of conventional concrete and a special class of fibre reinforced material, known as Strain Hardening Cementitious Composite (SHCC). Three SHCC beams were subject to four-point bending tests, differing in the interface surface preparation and curing method. Damage and delamination were gradually induced due to increasing loads in steps of 2.5 kN, and their propagation was tracked by the use of linear variable differential transformers and Digital Image Correlation technique. Dynamic hammer tests were also carried out to identify the natural frequency variation due to progressive damage. The outcome of this comparison allowed us to assess the capability of using a frequency-based monitoring technique for possible early-stage delamination detection of hybrid civil structures. To understand the influence of delamination on the dynamic response, a simplified finite element modelling approach of delamination was adopted. The induced damage was modelled in a simplified manner by reducing the stiffness of the elements in the damaged area. This model can be potentially integrable into large-scale numerical models for Structural Health Monitoring purposes.@en

A novel pile-driving technique, named Gentle Driving of Piles (GDP), that combines axial low-frequency and torsional high-frequency vibrations has been developed and tested recently. During the experimental campaign, several piles were installed onshore, making use of the GDP shaker. Besides those, a number of additional piles were installed using conventional pile-driving techniques, i.e. impact piling and axial vibratory driving. After the completion of the installation phase, the installed piles have been subjected to impact hammer tests with the following goals. First, the in-situ dynamic properties of the pile-soil system have been identified. Second, the post-installation soil state has been investigated, along with its evolution in time for each pile driving scenario. Preliminary analyses, of the data collected during the impact tests show dissimilar trends in the overall dynamic response between the piles installed with impact hammer and those installed with the axial and the GDP shakers.This observation suggests a difference in the post-installation dynamic behaviour of the pile-soil systems related to different pile-driving techniques. In this paper, a first attempt is made to identify the differences in the overall pile-soil dynamic behaviour of the piles installed by means of the three different pile-driving techniques.

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In this paper the dynamic behaviour of a high-rise building with complex structural system is studied. In some cases, to optimize the building design, the horizontal stability of the building is accomplished by the contribution of several structural components. This is the case of the JuBi tower, the building studied in this paper. The horizontal stability of the building is accomplished by three cores and outer walls. The cores and the walls are connected through the floors and the foundation. The data recorded during the experimental campaign carried out in this building show a double-peak behaviour corresponding to two closely spaced modes in the translational directions. This is caused by the weak coupling between the structural components. To study this phenomena, in this paper, a yet unique double-beam model is used. The parameters of the model are tuned so as to resemble the experimental response of the building. Results of the model evidence that the weak coupling is caused by the beams and the foundation. Also, it is shown that the two closely spaced modes correspond both to bending shape modes.

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In this paper, the energy dissipated in a tall building is identified by means of the energy flow analysis. This approach allows assessing energy dissipation within a specific domain or element of the structure. In this work, the focus is placed on the superstructure, which is the part of the building above the ground, and on the foundation. Damping operators for the superstructure and the foundation are formulated based on the identified energy dissipation in these parts of the building. The obtained damping operators are used to compute the modal damping ratios in a simplified model of the building. The modal damping ratios of the three lowest modes of vibration are compared to those identified in full-scale measurements by means of the half-power bandwidth method.

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Buildings are becoming taller, lighter, slenderer. These changing characteristics make tall buildings more sensitive to environmental loads, including wind gusts. A building is considered "tall" when its height and slenderness influence the design. Given the demand of improving building performance, the serviceability limit state (SLS) has become the most important design criterion of tall buildings. The structural serviceability is directly related to the building motions generated by wind gusts. These motions can influence the well-being of the building occupants. Whereas the human perception of movement is related to the jerk sensation, acceleration is the widely accepted parameter for measuring comfort level. In literature, a few well-established criteria for determining human perception to building vibrations can be found. In this work, the van Koten criteria are used to study human perception of building vibrations, using data collected from full-scale measurements of several high-rise buildings in The Netherlands. Whereas results clearly show that acceleration levels are barely perceptible, people still often feel insecure in the interior of high-rise buildings, meaning that human perception is extremely subjective. Dynamic systems are governed by their mass, damping, and stiffness. Damping can be understood as the energy dissipation in a system. Therefore, it determines the maximum acceleration that can be felt. Given its physical complexity, damping is the most uncertain parameter to be predicted. Presently, there are several damping predictors to determine damping in high-rise buildings. The resultant damping obtained by means of damping predictors is the result of the contribution of two main energy dissipation sources: the soil foundation interaction and the internal damping in the structure. Using these predictors, damping related to soil-foundation is a constant value, whereas structural damping increases with respect to the amplitude of vibration. Unfortunately, the use of these predictors result in large scatter compared to the experimentally identified damping values of buildings located in The Netherlands. Given that the parameters of these predictors are tuned based on full-scale experimental values, the discrepancy between experimentally identified damping of the buildings and the resultant values obtained by means of damping predictors is not easy to explain. In this work, a predictor based on the same principles, and tuned to fit the data collected from the full-scale measurements is presented and applied. Unfortunately, this predictor does not give enough insight to understand the behaviour of the dissipation mechanisms in a tall building. It is therefore the aim of this work to develop a tool for better assessing the energy dissipation in high-rise buildings to improve damping prediction. In a tall building, there are three types of energy dissipation (i.e the structural energy dissipation; soil energy dissipation and energy dissipation caused by the wind around the building). In this work, the aerodynamic damping caused by the wind around a building is considered negligible. To get a better overall damping prediction, an attempt to identify the contribution of the different damping sources to the overall damping is carried out. However, given the fact that wind loads cannot excite higher frequency modes in a tall building, the energy dissipation of specific areas of the structure cannot be adequately identified by using modal based techniques. Therefore, a different approach is needed to identify the energy dissipated in local areas without a modal description of the structure. In this work, the energy-flux analysis is proposed as a damping identification tool. This approach isolates a certain area of the structure to formulate an energy balance around it. The connection between this local area and the rest of the structure is made via the energy flux, which accounts for the energy coming in and going out of the local area. By doing this analysis, the energy dissipation of a local area can be identified. In Chapters 4 and 5, an energy-flux analysis is used to identify the energy dissipation in local areas of the structure. Then, a damping operator can be quantified. Another advantage of this approach is the added possibility of studying the behaviours of different damping operators by computing their energy dissipation. To validate the method two lab-scale structures, a lab-scaled beam, a lab-scaled steel-frame building and a full-scale high-rise building are used. This is done in the following manner. First, the structures are instrumented using accelerometers in the case of the lab-scale beam and accelerometers and strain gauges in the case of the lab-scale steel frame and high-rise building. Then, equivalent viscous damping is experimentally identified by means of the collected data. Second, a model representative of the structure to be analysed is developed. The model is made with continuous and discrete structural elements (e.g. beams, springs, dashpots). These models are used in order to interpret energy change, energy flux and dissipation energy. The energy balance can be formulated around a specific area of the model. Then, by making use of experimental data, the energy enclosed in this specific area can be computed, and energy dissipation can be identified. To compare percentages of critical damping, the energy dissipation is formulated in terms of a damping operator. This operator can be used to compute equivalent viscous damping, which makes use of the energy-flux analysis by comparing it to the experimentally identified equivalent damping values. Based on the results presented in this work, it is proven that this approach is a consistent framework for damping identification. In Chapter 6, a basic model for tall-building damping assessment during the design phase is presented. The model combines different models. The cone model describes the soil-foundation interaction and a Euler-Bernoulli beam model represents the building. Assuming a small vibration field, the mechanism responsible for the energy dissipation in the building is presumed to be directly related to the building's deformation. Therefore, the influence of building damping is studied based on the bending of the beam model used to describe the building. This influence varies with the change in the building deformation caused by different foundation stiffnesses. Likewise, the influence of soil-building interaction damping varies when changing the soil-foundation stiffness. Results provide evidence that the soil-foundation interaction of tall buildings may play an important role in the overall damping identification for certain soil characteristics, like the ones present in The Netherlands.@en

In this paper, the overall damping as function of the velocity of vibration of two tall structures subjected to wind is studied. The overall damping ratio is studied by means of two simple, but representative and complementary models and it is compared with that identified in two buildings in The Netherlands. In the models, the soil-structure interaction is computed using the cone model for embedded foundations developed by Wolf. Relevant parameters of the structure are identified by means of experimental data and Jeary's damping predictor. The results of the modelling show a large contribution of the foundation damping ratio to the overall damping ratio when soft soil conditions are considered.

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In this paper, identification of energy dissipation in the joints of a lab-scale structure is accomplished. The identification is carried out by means of an energy flow analysis and experimental data. The devised procedure enables to formulate an energy balance in the vicinity of the joints to obtain local energy dissipation. In this paper, a damping matrix based on the locally identified damping coefficients is formulated. The formulated damping matrix is later used in a five-degrees-of-freedom (5DOF) system for validation. The results obtained with the proposed method are in good agreement with the experimental data, especially in the low frequency range.

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The aim of this paper is to identify the local energy dissipation in a lab-scale structure by means of the energy flow analysis. In most of the existing approaches the damping is identified either in terms of the modal damping factors or at the material scale. In this paper, an alternative method to these global and material-based approaches by studying the energy flow around a certain part of the structure is proposed. The approach presented in this paper accounts for the energy flow through specific boundaries that surround the structural part of interest. Within this approach, the local energy dissipation can be calculated by isolating specific parts of the structure while taking into account the rest of the structure by means of the energy flux thorough the boundaries. This approach allows to identify both the total energy dissipation and the specific damping operator in the chosen part of the structure.

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In this paper the dynamics of a frame with bolted connections is studied both theoretically and experimentally. The connections are described using the Lund-Grenoble(LuGre) model. The problem of the dynamic response of the frame to a pulse load is studied using the Galerkin approach that reduces the governing equations to a set of nonlinear ODE's. They are latter solved numerically. It is shown that the theoretical predictions match the experimental observations well.

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