This thesis investigates the estimation of period lengthening (T˜/T) in structures using model updating, which assesses frequency shifts due to changes in boundary conditions, such as flexible bases. A 2D finite element (FE) model based on Timoshenko beam elements was developed and optimized through Sequential Least Squares Quadratic Programming (SLSQP) to align simulated dynamics with measured natural frequencies and mode shapes of a steel structure.

The research was divided into two phases. Phase one utilized synthetic modal data to validate the model updating process in an error-free environment, showing that the algorithm effectively resolves stiffness-to-mass ratios rather than individual properties. Period lengthening predictions proved more accurate and stable with stiff springs, while soft springs demonstrated higher sensitivity and discrepancy. Phase two applied real measurement data, yielding results consistent with synthetic data but revealing a “plateau” in the cost function, where optimal parameter determination was challenging due to model and measurement uncertainties.

The findings indicate that model updating is a feasible method for estimating period lengthening, especially for flexible foundations. However, results are sensitive to modeling and measurement uncertainties, necessitating careful evaluation to ensure optimization convergence and parameter precision. The study recommends further research to mitigate uncertainties and enhance the method’s applicability in high-rise building design.

In the Netherlands, there is an increasing need to create residential spaces in its already crowded cities to accommodate the growing population. Constructing high-rise buildings is one way to try to solve the issue. However, high-rise buildings are sensitive to wind-induced vibrations. The accurate prediction of the dynamic response is important in high-rise building design. In building design practice, calculating the dynamic response of high-rise buildings under wind loading typically involves simplifying the structure as a single degree of freedom system, characterised by the first eigenmode properties and subjected to a white noise spectrum. The damping and natural frequency of the building substantially impact its dynamic response. These parameters are challenging to predict with accuracy. Additionally, in the presence of soft soils, soil-structure interaction can play an important role in energy dissipation and influence the structure's natural frequency. In practice, soil-structure interaction is either disregarded or simplified.
In order to assess the effect of soil-structure interaction on the dynamic response of the building, this study models in a robust manner: the foundation, the tower structure, and the wind load. This newly developed model is addressed as the HF model. The investigation consists of a case study and a parametric study. Additionally, this study compares the predictions by the newly developed model with those obtained with a model as specified in the Eurocode. The case study provides a comparison between the models and the measured dynamic response of the New Orleans Tower. The parametric study looks into the influence of soil stiffness and material damping on the dynamic response of high-rise buildings. Furthermore, it investigates how these parameters affect the dynamic response of structures with various slenderness ratios.
The case study was used to demonstrate that the developed model accurately predicts the measured dynamic response of the New Orleans Tower in the along-wind direction. For all the examined dynamic properties, the error compared with the measurements was lower than 7%. In the case of the Eurocode model, the results demonstrate that, when using the natural frequency estimation recommended by the Eurocode, it provides a 30%–35% underestimation of the peak acceleration compared to measurements. This Eurocode model overestimates the natural frequency and overall damping, which causes it to underestimate peak acceleration. However, the natural frequency determined in the design phase of the New Orleans Tower was significantly lower than the value obtained with the recommended estimation method in the Eurocode. With this lower natural frequency, the peak acceleration is overestimated by around 50%. This underestimation of the natural frequency and overestimation of the damping provided acceptable conservative results. Although this showcases the importance of accurate predictions of both natural frequency and damping, having poor predictions that cancel out each other’s effects is not desirable.
The results from the parametric study support the findings from the case study. This shows that the case study’s findings apply to the more extensive range of building configurations investigated in the parametric study. In general, the Eurocode model, for slender structures on soft soil, overestimates the natural frequency and overall damping, which causes it to underestimate peak acceleration.
The parametric study revealed that the building's first natural frequency and global damping ratio are significantly influenced by the soil stiffness and soil material damping, which can result in various effects on the peak acceleration. In the case of soil material damping, not considering it at all or considering a higher value could lead to 20% overestimation and 40% underestimation of peak acceleration, respectively. Soil stiffness had more intricate effects since it affected the natural frequency and the amount of energy dissipated by the soil radiation damping, the soil material damping and the structure material damping. For particular combinations of parameters, soil stiffness had up to a 40% increase in the peak accelerations compared to the fixed foundation.
The results of this research show that the soil stiffness and soil material damping, for the ranges of properties relevant to the Netherlands, significantly influence the accurate predictions of the wind-induced dynamic response of high-rise buildings. Especially, there was found a higher influence on the dynamic response for the extreme cases of high slenderness ratio structures on very soft soils.

As buildings get taller and lighter, structural engineers are increasingly faced with the consequences of the dynamic response of high-rise buildings to wind. Damping is an important property for the dynamic response of high-rise structures, but is a combination of many mechanisms, which makes it a complex phenomenon to account for in the structural design. Empirical damping predictors currently exist, but a large scatter is found among predictors, as well as between predictors and identified damping from measurements. Damping values are prescribed in codes, but are not consistently conservative. Therefore, there is a strong desire from both structural engineers and researchers to obtain further understanding of damping behaviour in high-rise structures.

Damping identification techniques, such as the Half-power Bandwidth method and the Random Decrement technique are commonly used. However, these are not applicable to buildings with closely spaced modes, and require extensive measurements. Besides, they only provide a damping value, and cannot find damping of separate components of a system. A novel technique, the Energy Flux Analysis, approaches damping from an energy point of view, making it more widely applicable, and allowing for damping identification in components of a structure. The Energy Flux Analysis has been verified to lab structures, but its performance when applied to a high-rise structures using in situ measurements is still unknown.

The aim of this research is to investigate the sensitivities of and prerequisites for the application of the Energy Flux Analysis to high-rise buildings excited by wind using spatially limited measurements. The sensitivities were sought for in the uncertainty of required input for the Energy Flux Analysis: structure motion, which includes internal forces, wind load, data acquisition, and structural properties. The research was performed through application of the Energy Flux Analysis to the New Orleans tower in Rotterdam.

While the sensitivity to structural properties and the magnitude of measurements is limited, the Energy Flux Analysis demonstrated to be highly sensitive to the phase of structural motion, internal forces, and wind load. The first two points are relevant for computing the energy flux at the boundary of a system, when one is interested in damping in the superstructure and due to soil-structure interaction separately. The last point is relevant when one is interested in the total or superstructure damping.

The phase differences occurring between structure motion and internal forces are a direct result of damping. Material damping resulted in a phase difference between stress and strain in the numerical model, while a local damper resulted in a phase difference between structure motion at different locations. The many damping mechanisms occurring in a high-rise structure may each affect the phase of structure motion and internal forces differently. When these phase differences are not taken into account in the Energy Flux Analysis, for instance due to extrapolation of measurements, an erroneous result will be obtained. A brief investigation was performed as to whether these effects can be expected in true structures, but additional research is required.

The fluctuating wind load at the natural frequency of the structure is dominant for the flux of energy from wind to the structure, which is obtained by multiplication of the wind load with the structure velocity. Again, the phase of this wind load is highly important. When measured at one location, little is known about the phase of the wind load at other heights. Different approaches of extrapolating the measured wind load demonstrated a large scatter in the Energy Flux Analysis results. In this research, the Energy Flux Analysis found not to be repeatable, which was proven to be a direct result of the phase difference between the measured wind load and structure velocity. Possible causes for this varying phase difference were formulated.

It is essential, but due to the major advantages of the Energy Flux Analysis also profitable, to perform further research into its application to high-rise structures. Therefore, this study provides extensive recommendations mostly focused on simple numerical and lab experiments.