Railway bridge structural health monitoring and fault detection: state-of-the-art methods and future challenges

Railway importance in the transportation industry is increasing continuously, due to the growing demand of both passenger travel and transportation of goods. However, more than 35% of the 300,000 railway bridges across Europe are over 100-years old, and their reliability directly impacts the reliability of the railway network. This increased demand may lead to higher risk associated with their unexpected failures, resulting safety hazards to passengers and increased whole life cycle cost of the asset. Consequently, one of the most important aspects of evaluation of the reliability of the overall railway transport system is bridge structural health monitoring, which can monitor the health state of the bridge by allowing an early detection of failures. Therefore, a fast, safe and cost-effective recovery of the optimal health state of the bridge, where the levels of element degradation or failure are maintained efficiently, can be achieved. In this article, after an introduction to the desired features of structural health monitoring, a review of the most commonly adopted bridge fault detection methods is presented. Mainly, the analysis focuses on model-based finite element updating strategies, non-model-based (data-driven) fault detection methods, such as artificial neural network, and Bayesian belief network–based structural health monitoring methods. A comparative study, which aims to discuss and compare the performance of the reviewed types of structural health monitoring methods, is then presented by analysing a short-span steel structure of a railway bridge. Opportunities and future challenges of the fault detection methods of railway bridges are highlighted

Comparative analysis of offshore support structures for two-bladed large wind turbines (10+MW) in deep waters

The offshore wind market is developing towards exploiting wind resources in deeper water sites. Inevitably, this fuels new research and feasibility studies on alternative solutions for the wind turbine support structures. Within this context, this work aims at comparing three different support structure design concepts for a 14 MW two-bladed downwind wind turbine: an XXL monopile, a hybrid jacket-tower and a lattice tower. To ensure a fair comparability of the three design concepts, a load capacity analysis is first performed to assess the yield strength of each concept and guarantee a similar material utilization. The comparative analysis is then carried out in terms of total mass, dynamic behaviour of the interaction between rotor and support structure, soil-structure interaction and resulting hydrodynamic forces. Based on the given design constraints, the preliminary results of this study favour a lattice tower solution. The study also highlights peculiar dynamic phenomena such as veering, mode hybridization and mode coalescence for the dynamic interaction between the lattice tower and the two-bladed rotor which need to be taken into account during the design phase.Offshore Engineerin

A low-fidelity model for the dynamic analysis of full-lattice wind support structures

This work aims to develop a low-fidelity model for a lattice support structure for offshore wind applications. The proposed low-fidelity model consists of a sequence of regular Timoshenko beams, each of them characterized by homogenized mechanical and mass properties representative of the single bays of the reference space-frame structure. The homogenized elastic coefficients of the sequence of beams are then computed by means of two alternative procedures: case (a), via analytical expressions available in the literature and accounting for a partially isotropic behaviour; case (b) by means of an optimization procedure, with ad hoc calibration factors. The suggested methods to derive the homogenized elastic coefficients are then tested for both straight and tapered lattice structures. The prediction performance is evaluated in terms of estimation of the first five natural frequencies and mode shapes, response to dynamic loads, and ability to predict rotor-structure interaction phenomena. A parametric study is then performed to evaluate the potential and limitations of the proposed models. To bypass the optimization procedure (b), a data-driven approach is also proposed for the case of straight lattice structures. Overall, the developed low-fidelity model leads to a computational speed-up factor of at least 60. The prediction reliability of the low-fidelity model is discussed for a tapered and regular straight lattice structure. However, for the latter one, a more detailed comparative study between the various modelling assumptions is performed and discussed. With reference to the straight lattice tower, whenever an optimization procedure is used (case (b)), and with reference to a typical subset of the investigated geometrical parameter space, the mean prediction error of the first five natural frequencies is lower than 1%. On the other hand, for case (a) and for the same investigated subset, the mean prediction errors for the first two bending modes and the torsional mode are, 5.2%, 13.3% and 18.8%, respectively. These results are improved in case a data-driven regression model is used to predict the calibration factors, leading to mean prediction errors below 5% for the entire investigated parameter space.Hydraulic EngineeringMechanics and Physics of StructuresOffshore Engineerin

The role of p38 MAPK in the induction of intestinal inflammation by dietary oxysterols: modulation by wine phenolics

Dietary oxysterols are cholesterol auto-oxidation products widely present in cholesterol-rich foods. They are thought to affect the intestinal barrier function, playing a role in gut inflammation. This study has characterized specific cell signals that are up-regulated in differentiated CaCo-2 colonic epithelial cells by a mixture of oxysterols representative of a hyper-cholesterolemic diet. p38 MAPK activation plays a major role, while other signal branches, i.e. the JNK and ERK pathways, make minor contributions to the intestinal inflammation induced by dietary oxysterols. p38 transduction might be the missing link connecting the known NADPH oxidase activation, and the induction of NF-κB-dependent inflammatory events related to oxysterols’ action in the intestine. A NOX1/p38 MAPK/NF-κB signaling axis was demonstrated by the quenched inflammation observed on blocking individual branches of this signal with specific chemical inhibitors. Furthermore, all these signaling sites were prevented when CaCo-2 cells were pre-incubated with phenolic compounds extracted from selected wines made of typical Sardinian grape varieties: red Cannonau and white Vermentino. Notably, Cannonau was more effective than Vermentino. The effect of Sardinian wine extracts on intestinal inflammation induced by dietary oxysterols might mainly be due to their phenolic content, more abundant in Cannonau than in Vermentino. Furthermore, among different phenolic components of both wines, epicatechin and caffeic acid exerted the strongest effects. These findings show a major role of the NOX1/p38 MAPK/NF-κB signaling axis in the activation of oxysteroldependent intestinal inflammation, and confirm the concept that phenolics act as modulators at different sites of pro-oxidant and pro-inflammatory cell signals