Open Access

The Federal Institute of Material Research and Testing has performed many impact tests, from very small laboratory tests to very big “free-field” tests with heavy containers on stiff foundations. The first measurements have been done on a big foundation where it should be guaranteed that the foundation is rigid and the container is tested properly. Later, a smaller drop-test facility has been built on the ground inside an existing building. It had to be controlled by prediction and measurements to ensure that the drop test will not Damage the building. Tests from different heights on soft, medium, and stiff targets have been done to find out rules which allow to identify acceptable and unacceptable drop tests. Later, the biggest drop test facility has been built for masses up to 200 t. It was necessary for the design of the foundation to estimate the forces which occur during the drop tests. In addition, the acceptable tests should be selected and controlled by measurements where the impact duration is important. Different sensors, accelerometers, accelerometers with mechanical filters, geophones (velocity transducers), strain gauges, and pressure cells have been applied for these tasks. Signal transformations and model calculations have been used to check and understand the dynamic measurements. The simplest law is the conservation of the momentum which is a good approximation if the impact is short. If the soil under the foundation has an influence on the deceleration of the container, the maximum foundation velocity is lower than the simple estimation.

As demand for wind energy capacity increases and many old wind farms approach the end of their permitted lifetime, stakeholders must decide on the future of the existing structures – lifetime extension, partial or full repowering, or decommissioning. This complex decision combines technical, economic, environmental, and regulatory aspects. This contribution introduces the ReNEW research project, which aims to develop a modular quantitative framework, conceived as a digital decision-support tool to identify the end-of-life solution with the highest utility. Given the large number of modules in the project, this contribution focuses specifically on technical aspects, in particular the use of structural health monitoring (SHM) data for load reconstruction and lifetime assessment. The main developments and results concern a physics-based virtual sensors approach, combining a dynamic wind turbine model and a joint state and input estimator based on a Kalman filter. The proposed approach utilizes available measurements, such as strain and acceleration to a) reduce uncertainty in load estimation, b) provide additional information at uninstrumented or inaccessible locations such as the mudline, and c) reconstruct time histories of equivalent wind and wave loading. The related uncertainty quantification is discussed, and the method’s practical applicability is validated numerically and with real offshore wind farm data.

Suction bucket foundations offer significant advantages for offshore wind applications, enabling fast and cost-efficient installation. However, installation failures due to piping erosion remain a critical challenge, particularly in loose or highly permeable seabeds. Understanding the interplay between seepage flow, soil properties, and foundation geometry during suction installation is essential for improving design guidelines and installation strategies. In this contribution, fully-resolved numerical simulations are provided, that allow a detailed, grain-scale view of the suction installation process. A coupled Lattice Boltzmann-Discrete Element Method (LBM-DEM) framework is employed, in which fluid flow is resolved at a scale significantly finer than the particle size. This allows to capture pore-scale flow effects, particle rearrangements, and evolving soil resistance during installation, offering a higher level of detail compared to unresolved or continuum methods. The modeling approach is used to explore how soil characteristics and installation parameters influence the development of piping erosion and the resulting installation performance. By systematically varying key parameters, conditions are identified that promote either stable penetration or the onset of piping erosion, highlighting the critical role of seepage near the skirt tip. Beyond identifying failure envelopes, the simulations provide micromechanical insight into how local forces, flow paths, and soil resistance evolve as erosion initiates and progresses. These insights enable the critical examination of common assumptions regarding resistance distribution inside and outside the bucket during suction-driven installation. Additionally, the fully resolved simulation data can serve as a reference for calibrating and improving continuum-based models, bridging the gap between particle-scale mechanisms and engineering-scale predictive tools. The results illustrate how fully resolved LBM-DEM modeling can complement experimental and field studies, providing a powerful tool for developing more robust suction bucket installation strategies in challenging seabed conditions.

This presentation discusses a geology-informed probabilistic framework for propagating spatial and statistical uncertainties from raw in-situ measurements through to infrastructure-scale reliability analysis of offshore monopile foundations. Using CPT data from a real North Sea wind farm, Gaussian process regression with MCMC-based hyperparameter uncertainty quantification is employed to construct a 3D map of cone tip resistance. Site-to-site correlations transfer characterisation uncertainties into friction angle distributions, which are subsequently propagated into finite element-based probability of failure estimates, enabling a traceable uncertainty chain from in-situ measurement to foundation reliability assessment.

The structural health monitoring of bridges and slender towers is usually done by modal analysis. The recent research is focused on better tools for operational modal analysis, on removing environmental conditions and especially the influence of the temperature, on automated monitoring, statistical methods and the use of artificial intelligence. Many structures, however, are not as isolated as bridges or slender towers. They are coupled to other structures, like a floor in a building, or coupled to the soil such as buildings, foundations, or railway tracks. These structures need alternative methods for system and damage identification. This article, which is an extended version of the contribution to the special session about “other structures” of the 10th International Conference on Operational Modal Analysis, presents some additional or complementary methods to modal analysis and their application to different structures. Section 6.2 derives a method of system identification which is based on the measured frequency response functions and the transformed and weighted system equations. This simple method is applied to the dynamic driving behaviour of a car (Section 6.2) and to the modal analysis of beams and floors (Section 6.3). A special method to extract different mode shapes for closely spaced eigenfrequencies of neighbouring floors and its application to a large wooden multi-bay floor in a castle is presented in Section 6.3. The problem of local hammer excitation, global ambient excitation and global modes is addressed in Section 6.3 for the weakly coupled floor beams in the castle and in Section 6.4 where the condition of a truss member in a roof construction had to be analysed. In Section 6.5, a railway bridge is investigated by modal analysis and by a moving-load method. The quasi-static moving-load method with a slowly moving vehicle and with measured inclinations is further demonstrated for a long six-span footbridge, a short single span foot bridge, and on a laboratory beam in Section 6.6. In Section 6.7, damages of railway tracks are identified from the moving-load responses to normal train operation and by frequency response functions from hammer impacts. The railway tracks are coupled to the soil and the radiation damping into the soil prevents or hides any resonance so that modal analysis is no option. The soil-structure interaction is calculated by a combined finite-element boundary-element method, and the suitable soil properties as well as the extent of the damage are found by a manual model updating. The manual model updating for the identification of suitable soil parameters is demonstrated in Section 6.8 for a small building which is excited by ground vibrations.