sustainability while coping with high levels of phenomenological complexity and relatively low product maturity due to the limited amount of units deployed in varying operating conditions.

Presently, design, construction and operational practices are largely influenced by high-cycle fatigue as a primary degradation parameter. Empirical (inspection) practices are deployed as the key instrument to identify and mitigate system anomalies and unanticipated defects, inherently a reactive measure. This paper describes a paradigm-shift from predominant singular methods into a more

holistic and pro-active system approach to safeguard structural longevity. This is done through a short review of several synergetic Joint Industry Projects (JIP’s) from different angles of incidence on enhanced design and operations through coherent a-priori fatigue prediction and posteriori anomaly detection and -monitoring.","Floating Production Storage and Offloading assets (FPSOs); Structural Health Monitoring (SHM); Non-Destructive Evaluation/Testing (NDE/NDT); Risk Based Inspection (RBI); Condition Based Maintenance (CBM)","en","conference paper","DCMat Ageing Centre","978-94-6186-314-0","","","","","","","","","","","","" "uuid:f223d1ee-dfe7-4884-b856-35a99d6f366a","http://resolver.tudelft.nl/uuid:f223d1ee-dfe7-4884-b856-35a99d6f366a","Modal analysis of a concrete highway bridge: Structural calculations and vibration-based results","Miao, S.; Veerman, R.P.; Koenders, E.A.B.; Knobbe, A.","","2013","In the field of civil infrastructure, Structural Health Monitoring systems are implemented more and more frequently with the aim to safeguard the safety and service-life of structures such as bridges and tunnels. Changes in the integrity of the material and/or structural properties of this class of structures is known to adversely affect their performance, which can also be observed from the structures’ dynamic response, such as the natural frequencies, damping ratios and mode shapes. The procedure to obtain these response parameters is known as modal analysis. Two methods for obtaining these parameters are compared in this paper, one based on a careful analysis of measured vibration sensor data, and another one is based on a structural calculation using a Finite Element Method (FEM). The dynamic modal characteristics of a structure can be obtained by using vibration-based damage identification techniques such as Stochastic Subspace Identification (SSI). The SSI technique is capable of extracting modal parameters from output-only measurements, i.e. using raw data collected by simply monitoring a structure under its normal load. In this paper the application of SSI for the “Hollandse Brug”, which is a six-lane Dutch concrete highway bridge under in-service conditions, is described. The bridge is equipped with a sensor network of 145 sensors, including 34 vibration sensors (geo-phones). This paper demonstrates how the key modal parameters can be extracted by applying SSI to the sensor readings. To assess the quality of the sensor-based results, the modal parameters derived using SSI are compared with the results obtained from Finite Element Method (FEM) calculations. For the FEM calculation, the computer program Scia Engineer is used. The results of the two methods agree well, which shows that the SSI technique under output-only and in-service conditions is an effective tool for modal analysis, and thus a valuable method to be used in structural health monitoring systems.","stochastic subspace identification; stabilization diagram; output-only modal analysis; structural health monitoring; concrete bridge","en","conference paper","The Hong Kong Polytechnic University","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","","" "uuid:14c3d2a4-a931-41a4-a4e3-7f5f88aec7ff","http://resolver.tudelft.nl/uuid:14c3d2a4-a931-41a4-a4e3-7f5f88aec7ff","Data-intensive structural health monitoring in the infrawatch project","Veerman, R.P.; Miao, S.; Koenders, E.A.B.; Knobbe, A.","","2013","The InfraWatch project is a Dutch research project, aimed at developing novel techniques for large-scale monitoring of concrete infra-structures. The project involves a large bridge, fitted with multiple types of sensors that capture the high-resolution dynamic behavior of the bridge. With 145 sensors measuring at 100 Hz, a huge amount of data becomes available that describes various aspects of the bridge’s response to traffic and weather conditions, both long and short-term. A single truck passing the bridge already encompasses almost 50,000 readings, such that detailed modal analysis can be performed. At the same time, this data-intensive monitoring continues around the clock, as well as the calendar, such that more gradual effects like changes in temperature and traffic conditions can be tracked as well. This wealth of information is being analyzed in various ways ? which will be elaborated in this paper ? combining both computer science and civil engineering expertise. The InfraWatch project is a central project in the Dutch national research program “Integral Solutions for Sustainable Construction (IS2C)”, which is aimed at developing novel techniques for a next generation predictive simulation model for service life assessment. Other projects within this program are concerned with key degradation processes in structural concrete, such as ASR and chloride penetration. In the near future, the progress of such degradation processes will be measured by dedicated sensors, to be developed within these ‘sister projects’. Such direct degradation measurements will complement the indirect measurements currently performed, which essentially only monitor the dynamic load on the bridge. A lab experiment is currently being developed in the Stevin II laboratory of Delft University of Technology, where ASR and chloride penetration will be measured alongside with the dynamic deformations of a test beam under load while focusing on the mutual interaction of both the materials degradation processes and the structural response.","Structural Health Monitoring; sensor data; concrete bridge; output-only modal analysis; lab tests; material and structural degradation","en","conference paper","The Hong Kong Polytechnic University","","","","","","","","Civil Engineering and Geosciences","Structural Engineering","","","","" "uuid:a3f89f18-bf4d-4883-9dc6-c183968b4fdd","http://resolver.tudelft.nl/uuid:a3f89f18-bf4d-4883-9dc6-c183968b4fdd","Non-destructive testing techniques for the observation of healing effects in cementitious materials: An introduction","Grosse, C.U.; Van Tittelboom, K.; De Belie, N.","","2013","To develop an appropriate method of self-healing for cementitious materials including the right composition and amount of suitable healing agents it is required to investigate the healing efficiency for certain material mixtures. While some researchers evaluate the regain in compressive strength by means of destructive load tests, this method is obviously second best in particular for field applications. In a large EU project the best candidates among the non-destructive testing methods are investigated to be applied in small and large laboratory experiments as well as at real structures in-situ. The paper is giving an introduction to these techniques and addresses also issues of structural health monitoring used for example to monitor the healing effects on a long term basis and to assess the condition of the structure, where self-healing techniques are applied.","non-destructive testing; structural health monitoring; ultrasound; acoustic emission; vibration analysis","en","conference paper","","","","","","","","","","","","","","" "uuid:99ed4de4-f068-467f-970c-5d903bfc4a2a","http://resolver.tudelft.nl/uuid:99ed4de4-f068-467f-970c-5d903bfc4a2a","Wave Propagation in Thin-walled Composite Structures: Application to Structural Health Monitoring","Pahlavan, L.","Gürdal, Z. (promotor)","2012","In order for the increased use of fiber-reinforced composite structures to be financially feasible, employment of reliable and economical systems to detect damage and evaluate structural integrity is necessary. This task has traditionally been performed using off-line non-destructive testing (NDT) techniques. Safety enhancement programs and cost minimization schemes for repairs, however, have substantially increased the demand for real time integrity monitoring systems, i.e. structural health monitoring (SHM) systems, in the past few years. The real time feature imposes an additional constraint on SHM systems to be fast and computationally efficient. Among the existing approaches fulfilling these requirements, guided ultrasonic wave (GUW)-based methods are of particular interest, since they provide the possibility of finding small size defects, both at the surface and internal, and covering relatively large areas with reasonable hardware costs. Next to theses appealing features, there are certain complexities in utilizing GUWs for SHM of fiber-reinforced composites, that mainly arise from the multi-layer, anisotropic, and non-homogeneous nature of the material. In addition, the multi-mode character of GUWs further increases the complexity of the SHM problem in these materials. It is believed that computationally efficient methods for simulation of GUWs in composite structures can substantially contribute to the field of SHM. Such numerical tools do not only improve the understanding of the propagation of ultrasonic waves and their interaction with different damage types and boundary conditions, but can also make model-based damage identification techniques feasible in the context of on-line SHM. In this dissertation an improved framework for simulation of GUWs in composite structures is developed. The improvements are mainly brought about through the use of (i) physical constraints that reduces the dimensionality of the problem, (ii) improved approximation bases for spatial and temporal discretization of the governing equations, and (iii) efficient mathematical tools to enable the possibility of parallel computation. The formulated approach is a wavelet-based spectral finite element method (WSFEM), which offers the possibility of complete decoupling of the spatial and temporal discretization schemes, and results in parallel implementation of the temporal solution. Although the concept of the WSFEM was introduced a few years prior to this research, to the author's best knowledge, no general framework was proposed for dealing with 2D and 3D problems with inhomogeneity, anisotropy, geometrical complexity, and arbitrary boundary conditions. These issues are addressed in this dissertation in multiple steps as described below. 1- Improvement of the temporal discretization using compactly-supported wavelets, by computing the operators of the wavelet-Galerkin method over finite intervals, and demonstrating about 50% reduction in the number of sampling points, with the same accuracy, compared to the conventional wavelet-based approach. 2- Extension of the existing formulation of the 1D WSFEM based on an in-plane displacement field to 1D waveguides based on a 3D displacement field. In the 1D finite element formulation, spectral shape functions are employed which satisfy the governing equations, in which shear deformation and thickness contraction effects are also incorporated. The minimum number of elements for modeling 1D waveguides is used in this approach. 3- Formulation of a novel 2D WSFEM in which frequency-dependent basis functions are suggested for spatial discretization. Contrary to the conventional WSFEM, the presented scheme discretizes the spatial domain with 2D elements and does not require extra treatments for non-periodic boundary conditions. Superior properties of the formulation are shown in comparison with some time domain FEM schemes. 4- Generalization of the WSFEM and extension to 3D geometries. It is demonstrated that the standard spatial discretization schemes can be combined with the wavelet-Galerkin approach, to fully parallelize the temporal solution. A higher-order pseudo-spectral finite element method, i.e. spectral element method (SEM), is further adopted to attain spectral convergence properties over space and time. The developed WSFEM is subsequently employed in the passive time reversal (TR) method, which is a model-based approach for detection of load and damage location, and operates based on the time invariance of linear elastodynamic equations. It is shown that using the passive TR scheme, the problem of load and damage detection, which is essentially an inverse problem, can be solved in the form of a forward problem, thereby alleviating uniqueness and stability issues. A number of case studies and examples, numerical and experimental, are presented throughout this dissertation to better demonstrate the applicability of the proposed framework.","composite materials; guided waves; ultrasonics; structural health monitoring; wavelets; wavelet-Galerkin; time reversal; damage detection","en","doctoral thesis","","","","","","","","","Aerospace Engineering","Aerospace Structures and Computational Mechanics","","","",""