TY - CONF A1 - Zinas, Orestis A1 - Wilhelm, Sigrid T1 - CPT-based probabilistic design of monopile foundations N2 - This work was presented in the two-day workshop ‘Reliability-based methods in geotechnics’ organized by BAM and DGGT AK 2.15 in cooperation with the DGGT Academy. The presentation provides an overview of the sources of uncertainty in geotechnical analyses. A probabilistic 3D ground model of the cone-tip resistance from CPTs is developed utilizing sparse CPT data from a real offshore wind farm site in the North Sea. The predictive cone tip resistance model is used to derive a design property, such as the friction angle, using geotechnical transformation models. The friction angle profiles are then used to show an example of monopile design under uncertainty. T2 - Workshop: Einführung in die zuverlässigkeitsbasierte Bemessung in der Geotechnik 2024 CY - Berlin, Germany DA - 19.11.2024 KW - Geotechnical site-characterization KW - CPT KW - Spatial variability KW - Gaussian process regression KW - Design of monopiles KW - Offshore wind farms PY - 2024 AN - OPUS4-61716 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Zinas, Orestis A1 - Papaioannou, Iason A1 - Schneider, Ronald A1 - Cuéllar, Pablo A1 - Baeßler, Matthias T1 - 3D spatial modelling of CPT data for probabilistic preliminary assessment of potential pile tip damage upon collision with boulders N2 - Tip damage of monopiles from boulder collisions during installation has emerged as a critical design issue, primarily due to the combination of the widespread use of large-diameter piles and the complexity of the ground conditions at the available sites. Recently, a framework relating potential pile tip damage to cone tip resistance from Cone Penetration Tests (CPTs) has been proposed in the literature. Gaussian processes are powerful stochastic models that enable probabilistic spatial interpolation of soil data at any location within a site. On this basis, this study utilizes sparse CPT data from a site in the North Sea, to first develop an efficient Gaussian process regression model, which is used to derive a three-dimensional (3D) probabilistic predictive map of the cone tip resistance. Assuming deterministic loading conditions and a factual collision with a boulder of pre-defined properties, the cone tip resistance predictive model is subsequently used for a probabilistic preliminary assessment of potential pile tip damage. Results of the analysis are realistic 3D probability maps of potential damage that aim to support engineering judgment and contribute towards cost-effective site investigation planning and offshore wind farm design. T2 - 5th International Symposium on Frontiers in Offshore Geotechnics (ISFOG 2025) CY - Nantes, France DA - 09.06.2025 KW - CPT data KW - Gaussian process regression KW - Boulder impact KW - Preliminary pile tip damage assessment PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-634417 SN - 978-2-85782-758-0 DO - https://doi.org/10.53243/ISFOG2025-323 SP - 505 EP - 510 PB - International Society for Soil Mechanics and Geotechnical Engineering CY - London AN - OPUS4-63441 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Zinas, Orestis A1 - Papaioannou, Iason A1 - Schneider, Ronald A1 - Cuéllar, Pablo T1 - Multivariate Gaussian Process for 3D subsurface stratigraphy prediction from CPT and labelled borehole data N2 - Quantifying uncertainties in subsurface properties and stratigraphy can lead to better understanding of the ground conditions and enhance the design and assessment of geotechnical structures. Several studies have utilized Cone Penetration Test (CPT) data and employed Bayesian and Machine Learning methods to quantify the geological uncertainty, based on the Robertson’s soil classification charts and the Soil Behaviour Type Index (Ic). The incorporation of borehole data can reduce the stratigraphic uncertainty. Significant challenges can arise, however, mainly due to the intrinsic differences between field and laboratory-based soil classification systems, which can potentially lead to inconsistent soil classification. To this end, this study proposes a multivariate Gaussian Process model that utilizes site-specific data and: i) jointly models multiple categorical (USCS labels) and continuous (Ic) variables, ii) learns a (shared) spatial correlation structure and the betweenoutputs covariance, and iii) produces two types of dependent classification outputs. The results indicate that the integration of geotechnical and geological information into a unified model can provide more reliable predictions of the subsurface stratification, by allowing simultaneous interpretation of USCS and Ic profiles. Importantly, the model demonstrates the potential to integrate multiple variables of different types, aiming to contribute to the development of a methodology for joint modeling of geotechnical, geological and geophysical data. T2 - 7th International Conference on Geotechnical and Geophysical Site Characterization CY - Barcelona, Spain DA - 18.06.2024 KW - Geotechnical site-characterization KW - Probabilistic KW - Soil classification KW - Gaussian Process PY - 2024 SP - 1733 EP - 1740 AN - OPUS4-60712 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Zinas, Orestis A1 - Papaioannou, Iason A1 - Schneider, Ronald A1 - Cuéllar, Pablo T1 - Spatial modeling of heterogeneous geotechnical site investigation data using multivariate Gaussian Process N2 - This presentation is part of the Engineering Risk Analysis group open seminars. It aims to showcase the results of an ongoing study centered on developing a novel probabilistic methodology for 3D geotechnical site characterization. This methodology integrates data from Cone Penetration Tests (CPTs) and categorical borehole data. The presentation covers the mathematical details of the proposed Multivariate Gaussian Process model and demonstrates its application to a real geotechnical site in New Zealand. T2 - ERA Seminars CY - Munich, Germany DA - 24.07.2024 KW - Geotechnical site-characterization KW - CPT KW - Boreholes KW - Gaussian Process PY - 2024 AN - OPUS4-60716 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Zinas, Orestis T1 - 3D Probabilistic Site Characterization N2 - The aim of the study is to infer the soil stratification from the provided CPT and borehole data. We infer the soil type at any location within the domain of interest from the SBT index Ic (Robertson, 2009). This index can be directly related to the CPT data through an empirical correlation model. In addition, the soil classes contained in the borehole logs can be expressed as bounds on Ic. A log-transformation was applied to Ic, Y = ln(Ic), and Y was modelled by a 3D Random Field, with a fully Bayesian hierarchical Gaussian Process model to explicitly capture uncertainties. T2 - 19th eawe PhD Seminar CY - Hannover, Germany DA - 06.09.2023 KW - Wind Energy KW - Site-characterization KW - Probabilistic PY - 2023 AN - OPUS4-58940 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Zinas, Orestis T1 - 3D spatial modelling of CPT data for probabilistic preliminary assessment of potential pile tip damage upon collision with boulders N2 - Tip damage of monopiles from boulder collisions during installation has emerged as a critical design issue, primarily due to the combination of the widespread use of large-diameter piles and the complexity of the ground conditions at the available sites. Recently, a framework relating potential pile tip damage to cone tip resistance from Cone Penetration Tests (CPTs) has been proposed in the literature. Gaussian processes are powerful stochastic models that enable probabilistic spatial interpolation of soil data at any location within a site. On this basis, this study utilizes sparse CPT data from a site in the North Sea, to first develop an efficient Gaussian process regression model, which is used to derive a three-dimensional (3D) probabilistic predictive map of the cone tip resistance. Assuming deterministic loading conditions and a factual collision with a boulder of pre-defined properties, the cone tip resistance predictive model is subsequently used for a probabilistic preliminary assessment of potential pile tip damage. Results of the analysis are realistic 3D probability maps of potential damage that aim to support engineering judgment and contribute towards cost-effective site investigation planning and offshore wind farm design. T2 - 5th International Symposium on Frontiers in Offshore Geotechnics (ISFOG) CY - Nantes, France DA - 09.06.2025 KW - CPT data KW - Gaussian process regression KW - Boulder impact KW - Preliminary pile tip damage assessment PY - 2025 AN - OPUS4-63444 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Zinas, Orestis T1 - Stochastic variational Gaussian process for 3D site characterization N2 - This work was presented at the the 2nd Workshop on Future of Machine Learning in Geotechnics (2FOMLIG) & the 5th Machine Learning in Geotechnics Dialogue (5MLIGD), in Chengdu, China. In this study, we propose an efficient multivariate Gaussian process regression model, utilizing the Linear Model of Coregionalization, stochastic variational inference and Dirichlet-based transformations, to jointly model continuous CPT and categorical (USCS) borehole variables. The predictive performance of the model is assessed using a real dataset from a site located in Christchurch, New Zealand. T2 - 2nd Workshop on Future of Machine Learning in Geotechnics (2FOMLIG) & the 5th Machine Learning in Geotechnics Dialogue (5MLIGD) CY - Chengdu, China DA - 11.10.2024 KW - Geotechnical site-characterization KW - Cone Penetration Tests KW - Multivariate Gaussian process regression KW - Categorical borehole data KW - Stratigraphy prediction KW - Linear Model of Coregionalization PY - 2024 AN - OPUS4-61775 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Zinas, Orestis T1 - CPT-based probabilistic analysis of monopile foundations considering spatial and transformation uncertainties N2 - This study utilizes cone penetration testing data data from a real offshore windfarm project in the North Sea and presents a method for incorporating both, statistical and spatial uncertainties, in a reliability-based assessment of monopile foundations. Initially, a Gaussian Process regression model is constructed to predict a 3D map of the cone tip resistance and the associated uncertainties in the predictions and the hyperparameters, leveraging Markov Chain Monte Carlo methods. The CPT-based prediction is combined with a correlation derived from data collected at a nearby site to predict the probability distribution of the friction angle at a test location, which is subsequently used to evaluate the probability of failure for a monopile foundation with a finite element model. T2 - 9th International Symposiumon Geotechnical Safety and Risk (ISGSR) CY - Oslo, Norway DA - 25.08.2025 KW - Monopile design KW - Cone Penetration Test KW - Gaussian process regression KW - Bayesian Inference PY - 2025 AN - OPUS4-64001 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Zinas, Orestis T1 - Potentials of probabilistic approaches in offshore foundation installation N2 - This presentation discusses the potentials of probabilistic methods in offshore foundation installation, from the perspective of probabilistic ground models and data-driven site characterization. We discuss about methodologies for utilizing site-specific geotechnical (CPT) and geological data, aiming to construct an integrated ground model that can predict stratigraphic profiles and useful for geotechnical design parameters at any location within a 3D domain. The predicted parameters and stratigraphy are then used to predict the probability of potential pile tip damage, upon collision with a boulder. T2 - Colloquium Buckling of Offshore Wind Energy Structures CY - Berlin, Germany DA - 14.02.2024 KW - Wind KW - Offshore KW - Buckling KW - Probabilistic KW - Ground PY - 2024 AN - OPUS4-59538 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Zinas, Orestis T1 - A Modular Gaussian Process Regression Toolbox for Uncertainty Aware Geotechnical Site Characterization N2 - A modular Gaussian Process Regression toolbox for efficient large-scale geotechnical site characterization from sparse 1D data was presented at the Third Future of Machine Learning in Geotechnics (3FOMLIG), Florence, Italy, October 16, 2025. The PyTorch/GPyTorch-based framework enables multivariate modeling of correlated soil properties and joint regression-classification of continuous CPT parameters with categorical soil units through Dirichlet transformations. Stochastic Variational Inference reduces computational complexity from O(N³) to O(M³), enabling GPU-accelerated processing of 100,000+ measurements. Validated on a 33 km² North Sea offshore wind farm site with 100+ sparse investigation points, the toolbox generates uncertainty-aware 3D predictions, supporting univariate, multivariate (LMC), and sequential multi-group modeling strategies. T2 - Third Future of Machine Learning in Geotechnics (3FOMLIG) CY - Florence, Italy DA - 15.10.2025 KW - Probabilistic site-characterization KW - Gaussian process regression KW - Bayesian inference KW - Offshore Wind Farms PY - 2025 AN - OPUS4-64423 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Wiehle, Philipp A1 - Härder, M. A1 - Strangfeld, Christoph T1 - Moisture behaviour of earth block masonry under natural climate conditions – experimental and numerical studies N2 - The compressive stength of unstabilised earth masonry depends on the moisture content. Knowledge of the moisture content is necessary in order to be able to account for the impact of moisture on the structural design of earth block masonry. For conventional building materials it is possible to precisely forecast the component moisture according to the layered structure on the basis of hygrothermal simulations. However , it is still not clear to what degree these numerical calculations can offer valid results for earth building materials. Earth building materials have a number of special properties related to moisture storage and moisture transport that differ significantly from the physical simplifications that are a component of existing material models. The swelling and shrinking of earth materials and their organic components results in changes to the pore space, the sorption behaviour exhibits a clear hysteresis, and the experimental determination of hygrothermal parameters in continuous contact with liquid water is almost impossible. To adequately forecast the moisture content of earth block masonry under natural climate conditions, extensive investigations of the moisture behaviour of load-bearing earth block masonry have been carried out within the framework of this project. These efforts began with the performance of magnetic resonance spectroscopic tests on two load-bearing earth blocks, in order to quantify the adsorption and desorption processes at relative humidities of between 50 % and 90 % under controlled, isothermal laboratory conditions. Once this had been done, a modified test setup was used to determine the water absorption coefficient , from which the liquid transport coefficients were derived. Based on the hygrothermal parameters values that were thus determined, the model was calibrated using the WUFI software program [7]. Finally, long-term moisture measurements were conducted on an earth block masonry wall that was ex-Increasing shortages of raw materials and rising energy prices are resulting in continuous growth in the demand for earth construction. In comparison to conventional building materials, earth building materials offer three significant advantages that have become even more important in light of the energy crisis in 2021 and the associated increase in the price of building supplies by approx. 40 percent [1]. Firstly, water solubility makes it possible to fully separate and recover all of the material components, and in particular the sand component. Secondly, energy-intensive firing processes, such as those required for cement production or brick manufacture, are eliminated. And thirdly, earth is a local raw material that is available in large quantities [1]. However, the load-bearing capacity of earth building materials is very much dependent on the moisture content. An increase in the relative humidity results in a reduction in the clay mineral cohesion , and this in turn results in a decline in both the compressive strength and the modulus of elasticity. In this regard, the mechanical properties of earth block masonry change in inverse proportion to the relative humidity. In other words, with every percentage point increase in relative humidity, both the compressive strength and the modulus of elasticity decline by one percent [2] [4]. The internal walls of heated living areas are generally only subject to relatively small fluctuations in relative humidity (between 40 % and 60 %) [5], and short periods in excess of these levels (such as in bathrooms or kitchens) only lead to a significant increase in the moisture content of the uppermost layers [6]. Exterior walls, on the other hand, are subject to large seasonal fluctuations in temperate climates, with a relative humidity in excess of 90 % in winter months. However, the exterior walls of heated living areas must be insulated in accordance with the German Buildings Energy Act (GEG), and with masonry this is generally done us T2 - LEHM 2024 – 9. Internationale Fachtagung für Lehmbau CY - Weimar, Germany DA - 27.09.2024 KW - Earth stone KW - Masonry KW - Material moisture KW - Moisture monitoring KW - Hygrothermal simulations PY - 2024 SP - 1 EP - 10 AN - OPUS4-61220 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wiehle, Philipp A1 - Baier, Johanna A1 - Thiele, Marc T1 - Structural Design of Earth Masonry in Accordance with Eurocode 6 – Considering Moisture Content and E/fk Ratio N2 - The load‐bearing behaviour of earth masonry is similar to conventional masonry, with two key differences: compressive strength and Young's modulus are dependent on moisture content, and the ratio between Young's modulus and characteristic compressive strength (E/fk) is significantly lower. The current design concept according to the Lehmbau Regeln does not explicitly address these factors, relying instead on a general safety margin, leading to an underestimation of the load‐bearing capacity of modern earth masonry.Compression tests on small‐scale masonry specimens and storey‐high walls revealed that compressive strength and Young's modulus decrease inversely proportional to the increase in relative humidity. Additionally, it was found that conventional masonry design guidelines overestimate the buckling resistance of earth masonry due to its low E/fk ratio of ∼440. However, this ratio remains independent of moisture content, simplifying structural design, as the load‐bearing capacity is only influenced by wall slenderness.The study's findings form the foundation for the newly published German design standard DIN 18940, which explicitly considers moisture content through service classes with moisture factors and addresses the low E/fk ratio with a bilinear adaptation of the reduction factor considering the slenderness. Along with the introduction of the semi‐probabilistic design concept and rigid‐plastic determination of cross‐sectional load‐bearing capacity, modern earth masonry can now be applied in buildings up to four storeys. T2 - Earth Builder Summit CY - Biberach, Germany DA - 06.03.2025 KW - Service class KW - Earth masonry KW - Structural design KW - Moisture PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-637803 DO - https://doi.org/10.1002/cepa.3287 SN - 2509-7075 VL - 8 IS - 1 SP - 9 EP - 21 PB - Ernst & Sohn GmbH AN - OPUS4-63780 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wedel, F. A1 - Pitters, S. A1 - Herrmann, Ralf A1 - Schneider, Ronald A1 - Hille, Falk A1 - Hindersmann, I. T1 - Guideline for the strategic application of monitoring of road bridges in Germany N2 - Engineering structures are an important part of our transport infrastructure. Their failure is associated with high safety risks and economic damage. Ensuring the availability of these constructions and guaranteeing their operational safety are thus important tasks. Currently, maintenance of engineering structures is a reactive process and therefore not yet a predictive process. Every 3 to 6 years, the structures are visually inspected, all damages are documented and a condition grade is assigned to the structure based on the detected damages. Continuous data-providing methods such as monitoring are used only very occasionally. With the help of monitoring, condition data about the structures are continuously collected, which can be used for a better assessment of the structures. On the one hand, this would increase safety of engineering structures, and on the other hand, it makes the shift towards predictive maintenance management based on real-time data and predictions, where the onset of damage is detected before it occurs, possible in the first place. Monitoring plays therefore an important role in the management of the infrastructure. It is a crucial a step towards the digitalisation of our infrastructure and existing processes. Although there are many use cases for monitoring that have already been successfully implemented, monitoring is not yet widely used by German road authorities due to several challenges that were also identified within the scope of the project. Therefore, a guide has been developed in which the current obstacles related to monitoring are identified and possibilities for integrating monitoring into existing processes are offered. To ensure optimal alignment with the needs of road authorities, both an online survey and a workshop have been conducted. The results are summarised in a brochure that is made available to authorities to improve the use of monitoring in Germany. This paper presents the guideline and the brochure. T2 - 10th European Workshop on Structural Health Monitoring (EWSHM 2024) CY - Potsdam, Germany DA - 10.06.2024 KW - Verkehrsinfrastrukturen KW - Engineering Structures KW - Bridges KW - Structural Health Monitoring KW - Guideline PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-612821 UR - https://www.ndt.net/search/docs.php3?id=29582 DO - https://doi.org/10.58286/29582 SN - 1435-4934 VL - 29 IS - 7 SP - 1 EP - 8 PB - NDT.net GmbH & Co. KG CY - Mayen AN - OPUS4-61282 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Vollmer, Malte A1 - Degener, Sebastian A1 - Bolender, Artjom A1 - Bauer, Andre A1 - Liehr, Alexander A1 - Stark, Andreas A1 - Schell, Norbert A1 - Barriobero-Vila, Pere A1 - Requena, Guillermo A1 - Niendorf, Thomas T1 - Time resolved insights into abnormal grain growth by in situ synchrotron measurements N2 - Large oligo-crystalline or single-crystalline metallic materials are of great interest for numerous applications, and a recently developed strategy for promoting abnormal grain growth induced by a cyclic heat treatment opens up new opportunities to manufacture single crystals with a size of several centimeters. So far, the entire available knowledge on this kind of abnormal grain growth has been elaborated based on time discrete observations and, thus, detailed insights into the interplay of elementary mechanisms are still lacking in open literature. The present study reveals time resolved insights into this kind of abnormal grain growth for the first time. It was possible to break down the influence of the individual heat treatment phases by in situ synchrotron high energy X-ray diffraction analysis during cyclic heat reatment. The results obtained not only help to gain a deep understanding of the abnormal grain growth mechanisms, they will also be the basis for an adjustment of the cyclic heat treatment process to improve its efficiency and to eventually obtain even larger single crystals. KW - Single crystals KW - Grain growth method KW - Synchrotron diffraction KW - High-energy X-ray diffraction KW - Grain boundary migration PY - 2023 DO - https://doi.org/10.1016/j.actamat.2023.119168 SN - 1359-6454 VL - 257 SP - 1 EP - 9 PB - Elsevier Ltd. AN - OPUS4-62188 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Viefhues, Eva A1 - Döhler, M. A1 - Simon, Patrick A1 - Herrmann, Ralf A1 - Hille, Falk A1 - Mevel, L. ED - Cunha, A. ED - Caetano, E. T1 - Stochastic subspace-based damage detection of a temperature affected beam structure N2 - Structural health monitoring (SHM) of civil structures often is limited due to changing environmental conditions, as those changes affect the structural dynamical properties in a similar way like damages can do. In this article, an approach for damage detection under changing temperatures is presentedand applied to a beam structure. The used stochastic subspace-based algorithm relies on a reference null space estimate, which is confronted to data from the testing state in a residual function. For damage detection the residual is evaluated by means of statistical hypothesis tests. Changes of the system due to temperature effects are handled with a model interpolation approach from linear parameter varying system theory. From vibration data measured in the undamaged state at some few reference temperatures, a model of the dynamic system valid for the current testing temperature is interpolated. The reference null space and the covariance matrix for the hypothesis test is computed from this interpolated model. This approach has been developed recently and was validated in an academic test case on simulations of a mass-spring-damper. In this paper, the approach is validated experimentally on a beam structure under varying temperature conditions in a climate chamber. Compared to other approaches, the interpolation approach leads to significantly less false positive alarms in the reference state when the structure is exposed to different temperatures, while faults can still be detected reliably. T2 - 10th International Conference on Structural Health Monitoring of Intelligent Infrastructure, SHMII 10 CY - Online meeting DA - 30.06.2021 KW - Damage detection KW - Subspace methods KW - Temperature effects KW - Model interpolation KW - Climate chamber KW - Laboratory beam structure PY - 2021 SP - 1 EP - 6 AN - OPUS4-52999 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Viefhues, Eva A1 - Döhler, M. A1 - Hille, Falk A1 - Mevel, L. T1 - Fault detection for linear parameter varying systems under changes in the process noise covariance N2 - Detecting changes in the eigenstructure of linear systems is a comprehensively investigated subject. In particular, change detection methods based on hypothesis testing using Gaussian residuals have been developed previously. In such residuals, a reference model is confronted to data from the current system. In this paper, linear output-only systems depending on a varying external physical parameter are considered. These systems are driven by process noise, whose covariance may also vary between measurements. To deal with the varying parameter, an interpolation approach is pursued, where a limited number of reference models -- each estimated from data measured in a reference state -- are interpolated to approximate an adequate reference model for the current parameter. The problem becomes more complex when the different points of interpolation correspond to different noise conditions. Then conflicts may arise between the detection of changes in the eigenstructure due to a fault and the detection of changes due to different noise conditions. For this case, a new change detection approach is developed based on the interpolation of the eigenstructure at the reference points. The resulting approach is capable of change detection when both the external physical parameter and the process noise conditions are varying. This approach is validated on a numerical simulation of a mechanical system. T2 - IFAC World Congress 2020 CY - Online meeting DA - 11.07.2020 KW - Linear parameter varying systems KW - Fault detection KW - Changing process noise KW - Subspace-based residual KW - Model interpolation PY - 2020 SP - 13858 AN - OPUS4-51617 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - THES A1 - Viefhues, Eva T1 - Subspace-based damage detection in engineering structures considering reference uncertainties and temperature effects N2 - Automated vibration-based damage detection is of increasing interest for structural health monitoring of engineering structures. In this context, stochastic subspace-based damage detection (SSDD) compares measurements from a testing state to a data-driven reference model in a statistical framework. In this thesis theoretical developments have been proposed to improve the robustness of SSDD for realistic applications conditions. First, a statistical test has been proposed considering the statistical uncertainties about the model obtained from the reference data. This leads to a precise description of the test’s distribution properties and damage detection thresholds. Second, an approach has been developed to account for environmental effects in SSDD. Based on reference measurements at few different environmental conditions, a test is derived with respect to an adequate interpolated reference. The proposed methods are validated in numerical simulations and applied to experimental data from the laboratory and outdoor structures. KW - Damage detection KW - Subspace methods KW - Vibrations KW - Uncertainty quantification KW - Environmental effects KW - Civil structures PY - 2021 SP - 1 EP - 191 CY - Universite de Rennes AN - OPUS4-55774 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Viefhues, Eva T1 - Fault detection for linear parameter varying systems under changes in the process noise covariance N2 - Detecting changes in the eigenstructure of linear systems is a comprehensively investigated subject. In particular, change detection methods based on hypothesis testing using Gaussian residuals have been developed previously. In such residuals, a reference model is confronted to data from the current system. In this paper, linear output-only Systems depending on a varying external physical parameter are considered. These systems are driven by process noise, whose covariance may also vary between measurements. To deal with the varying parameter, an interpolation approach is pursued, where a limited number of reference models { each estimated from data measured in a reference state { are interpolated to approximate an adequate reference model for the current parameter. The problem becomes more complex when the different points of interpolation correspond to different noise conditions. Then con icts May arise between the detection of changes in the eigenstructure due to a fault and the detection of changes due to different noise conditions. For this case, a new change detection approach is developed based on the interpolation of the eigenstructure at the reference points. The resulting approach is capable of change detection when both the external physical parameter and the process noise conditions are varying. This approach is validated on a numerical simulation of a mechanical system. T2 - 21st IFAC World Congress CY - Berlin, Germany DA - 13.07.2020 KW - Linear parameter varying systems KW - Fault detection KW - Changing process noise KW - Subspace-based residual KW - Model interpolation PY - 2020 AN - OPUS4-52366 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Viefhues, Eva T1 - Stochastic subspace-based damage detection of a temperature affected beam structure N2 - Structural health monitoring (SHM) of civil structures often is limited due to changing environmental conditions, as those changes affect the structural dynamical properties in a similar way like damages can do. In this article, an approach for damage detection under changing temperatures is presentedand applied to a beam structure. The used stochastic subspace-based algorithm relies on a reference null space estimate, which is confronted to data from the testing state in a residual function. For damage detection the residual is evaluated by means of statistical hypothesis tests. Changes of the system due to temperature effects are handled with a model interpolation approach from linear parameter varying system theory. From vibration data measured in the undamaged state at some few reference temperatures, a model of the dynamic system valid for the current testing temperature is interpolated. The reference null space and the covariance matrix for the hypothesis test is computed from this interpolated model. This approach has been developed recently and was validated in an academic test case on simulations of a mass-spring-damper. In this paper, the approach is validated experimentally on a beam structure under varying temperature conditions in a climate chamber. Compared to other approaches, the interpolation approach leads to significantly less false positive alarms in the reference state when the structure is exposed to different temperatures, while faults can still be detected reliably T2 - 10th International Conference on Structural Health Monitoring of Intelligent Infrastructure, SHMII 10 CY - Online meeting DA - 30.06.2021 KW - Damage detection KW - Subspace methods KW - Temperature effects KW - Model interpolation KW - Climate chamber KW - Laboratory beam structure PY - 2021 AN - OPUS4-53000 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Thiele, Marc A1 - Makris, Ralf ED - Aign, J. T1 - Reinforcement bar and reinforcement bar splicing systems under impact loading – Experimental tests and test specification N2 - Reinforced concrete is a widely used material for power generation structures, where load scenarios like impact loadings need to be considered. In this context mechanical splicing systems for the connection of reinforcement bars are of specific interest and impact resistance for the splicing systems has to be verified. High speed tensile tests need to be performed on splicing systems for reinforcement bars to confirm the capability of the coupler to resist impact loading. Furthermore, the ability of the reinforcement steel to dissipate energy by ductile behaviour with pronounced plastic strains should be confirmed by these tests. During the last decades comprehensive experiences were developed at BAM performing high speed tensile tests on reinforcement bars as well as on several splicing systems. For the lack of available standards defining these tests in detail an appropriate test procedure was developed and continuously optimized during this period at BAM. The test procedure is partially based on testing principles adapted from available standards. The main intention behind this test procedure is to perform high-speed tensile tests with a specific constant strain rate generated at the specimen. Furthermore, main objective was to establish a procedure to guarantee the comparability of test results for different diameter of reinforcement as well as for different types of couplers. Besides the pure execution of the high-speed tensile tests, the test specification also declares how to evaluate the measurements and the test results. Finally, some typical results will be presented in this contribution. T2 - SMIRT 26 CY - Potsdam, Germany DA - 10.07.2022 KW - Impact KW - Coupler systems KW - High-speed KW - Reinforcement PY - 2022 SP - 1 EP - 10 AN - OPUS4-55422 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -