In the last few years, the construction of new high-speed (HS) railways across Europe, as well as in many other countries, has required many different bridges and viaducts. Together with classical concrete solutions, new steel–concrete composite typologies have been developed, giving light and cheap structures. Despite these studies and applications, some concerns still remain about the definition of reliable models for the evaluation of their actual dynamical behaviour under HS train passage. In particular, the influence of many structural and non-structural components, such as cross-girders and ballast, are still not well recognised. In this paper, open problems related to the dynamical assessment and modelling of new steel–concrete four-parallel-girder and box-girder solutions are exposed and analysed. A suitable procedure, based on operational modal analysis, model updating and train–bridge interaction analysis is applied to two bridges, recently built in the new Italian HS network, in order to assess and verify their dynamic behaviour under operative conditions.

Structural assessment of historical constructions is a particular issue as these structures were built with technical knowledge and construction methods based on in-field experience and on the observation of previous failures and successes of similar buildings. Their structural behavior is influenced by numerous aspects, sometimes not completely known (geometry, structural schemes and details, material mechanical properties), which often results in historical structures inadequate to achieve the safety level required for new constructions. In the case of earthquakes, these structures can suffer heavy local or global damages that sometimes lead to collapse. Thus static and seismic vulnerability assessment of historical buildings should therefore be performed by proper methodologies that differ from those used for new constructions. In Italy, an official document (Direttiva del Presidente del Consiglio dei Ministri [DPCM] 2007, revised in 2011) was released, defining a step-by-step procedure for data acquisition and vulnerability assessment of Cultural Heritage buildings. Such procedures can be coupled with new survey technologies such as terrestrial laser scanning (TLS), which, for performing a high-detailed three-dimensional geometrical survey, can provide detailed structural models refining the assessment results. In this study, the DPCM procedure is applied to Santa Maria del Mar Church in Barcelona (Spain) for seismic vulnerability assessment, using TLS three-dimensional survey and finite element analysis.

Tie-rods are structural elements of crucial importance in ancient buildings to ensure structural integrity and safety, so the assessment of their effectiveness via an estimation of the axial load is of great importance. Dynamic techniques are often employed using accelerometers to measure the frequency response of the tie-rods. In this work, the frequency response of tie-rods is obtained with acoustic recording, thus introducing general-purpose microphones to potentially replace more expensive and complex sensors in this application. Two microphones were tested, one of known technical characteristics, and a second for which they were unknown. A procedure was designed to overcome the technical limitations of the latter, and two experimental campaigns were conducted to test the proposed method.

Steel–concrete composite bridge solutions have been more and more exploited in the new high-speed (HS) lines of European railway networks. New design solutions, introduced during a period of quick expansion for railway networks, amplified open problems related to dynamic effects, train–bridge interaction phenomena, fatigue loadings, structural modelling, fatigue life and comfort. In this article, results obtained by long-term dynamic monitoring of Sesia viaduct, a medium span double-box composite bridge of the new Italian HS network, are described and analysed. Structural modal properties were determined in order to evaluate the real-time dynamic behaviour and its correlation with environmental conditions. A suitable numerical procedure was then implemented in order to identify typology, length and velocity of trains crossing the bridge, to evaluate the intensity of deck vertical accelerations as a function of train speed and to obtain a reliable evaluation of real traffic spectra. A final fatigue assessment on welded connections was executed evaluating fatigue spectra by the aforementioned real traffic spectra and assuming S–N curves obtained by suitably executed experimental tests.