In the last decades, an increasing number of researchers has been devoted to damage detection in civil structures. Structural Health Monitoring techniques allow to monitor structures, localizing and in some cases, quantifying damages to prevent failures. Since a damaged structure is characterized by a change in the dynamic properties and given the global nature of the vibration based methods, in the present work a vibration based method for damage detection in beam structures is presented. The proposed technique exploits the modal characteristics of the structure to detect damages, evaluating variations in the dynamic flexibility matrix between the healthy and the damaged state. The advantage of this approach stems from the possibility to use only the lowest eigenfrequencies and mode shapes, that can be easily derived from the dynamic monitoring of the structure. Though in real case scenarios, structures can be instrumented only with a limited number of accelerometers, the developed damage localization and quantification technique can be successfully applied also when a restricted number of mode shape components is known. To this aim, a two step procedure based on the expansion of the reduced number of modal components to compute the structure flexibility matrix is proposed. In the first step, the known modal components φ^k of the damaged structure are completed using an iterative modal expansion technique, which utilizes the stiffness matrix of the structure. In the expansion procedure, only a subset of known modal components φ^s, with s < k, is used, while the remaining ones are used as control components (φ^c). Note that the stiffness matrix of the damaged structure is unknown. Hence, the subset φ^s of modal components using n × m different stiffness matrices is expanded, by considering damage in n possible locations, being the beam divided in n finite elements, with m damage intensities. By doing so, a dataset of n × m expanded modes is generated, where the set φ_(n,m)^e corresponds to the expanded modes related to the damage scenario (n, m). Note that every set of modes φ_(n,m)^e includes the control components φ_(n,m)^c. Thus, to identify the damage location and extent, the total modal assurance criterion (TMAC) between φ_(n,m)^c and φ^c is calculated. The damage scenario ( n*,m*), which provides the largest TMAC is selected for the following step. In the second step, this identification is verified using a flexibility based index. If the n* beam element indicated by the index corresponds to the one identified in the first step, the damage location and extent are determined. If this does not occur, the algorithm iterates the procedure until the two step check is verified. The proposed procedure is experimentally validated on a reinforced concrete free free beam with laboratory tests in which the structure is progressively damaged.

This article presents the studies regarding the assessment of the damping performance of Stockbridge dampers on an overhead high-voltage transmission line conductor and their impact on the corresponding fatigue lifetime estimation. To increase the understanding of the dynamic behaviour of Stockbridge dampers, a test setup was designed and constructed to accommodate a segment of a conductor following the normative prescriptions of CIGRÉ. A classical modal identification was initially conducted to characterise the corresponding dynamic behaviour without and with an added Stockbridge damper. The Power Method was used to assess the conductor self-damping at different vibration amplitudes, without and with the installed Stockbridge damper positioned on various sections of the conductor. Furthermore, a set of sensors were installed on the conductor, close to the anchorage, to simulate the VIBREC device and permit the analysis of the damper's influence in estimating the conductor's lifetime. Through the analysis of the database collected with the tests, it was possible to assess the dynamic properties of the conductor, identify the reduction of the vibration amplitudes enabled by the Stockbridge damper, and characterise the consequent increase in the conductor's lifetime.

Many novel approaches to structural health monitoring use machine learning techniques that require large data sets to train the system effectively. In an effort to enhance available data sets for bridges, for these approaches to become wider applicable, a population-based structural health monitoring (PBSHM) approach is being developed that seeks to facilitate transfer learning between notionally similar structures (i.e. sharing data). PBSHM, whilst in its infancy, has been trialled on several different structures to date. Bridges are some of the largest structures to be described with Irreducible Element (IE) Models for Attributed Graph (AG) comparisons to be carried out. For the first pool of bridges, the Canonical Form AG comparison results were indicatively positive, however, Maximum Common Subgraphs (MCS) required interrogation to tell the relevance of partial matches, highlighting the need for revisions to the bridge IE models to provide more meaningful similarity metrics. Therefore, this paper proposes a new concept for bridge IE Models that treats a bridge as a series of structures that interact via shared boundaries, as opposed to a single structure. Instrumentation of bridges (data collection) is often limited to portions of bridges being monitored/assessed, and datasets that historically exist for bridges are often confined to those portions of the bridge, e.g. Deck, Abutment, Pier. Further, as the distance an element is from measurement instrumentation increases, less information can be extracted about that element. Therefore, the extents of the new bridge IE models are set to mimic the extents of parts of bridges that common datasets pertain to (e.g. deck, abutment, pier). The revised model extents reduce the number of elements describing each structure/part of the bridge, increasing the influence of each matched element and relationship on the resulting similarity metrics. Specifically, for areas of partial matches, the relevance of the partial match is more intuitively reflected in the similarity metrics obtained for both deck and support structures.