This paper includes a review of the several calculation methods available to calculate the modal damping ratio from dynamic events obtained in structural health monitoring of bridges. A comparative analysis among methods involving the logarithmic decrement, bandwidth applied over the spectrum, adjustment to the theoretical curve and random decrement technique is included. Additionally, an alternative calculation method based on signal spectra reduction has been formulated, whose main advantage lies in the fact that it directly allows the study of multiple-degrees-of-freedom systems, which describe typical structures, without the need for applying filters; this method gives extremely precise values despite simplification of the calculations. First, a comparative analysis is carried out on a set of theoretically simulated waves. In these cases, although there are differences in detail, the obtained results are reasonably close to the theoretical values. Second, an analysis of the registered accelerograms during a test campaign of a real structure, the viaduct “The Arches of Alconétar”, is performed. It has been observed that in this case, unlike what happens with the theoretical simulations, the obtained results significantly vary depending on the selected calculation method. For this reason, it is important to know which method has been used to calculate the modal damping ratio in structural health monitoring systems, as well as to be cautious in setting thresholds.

This contribution presents the results of numerical simulations in which a high-pier viaduct under lateral and vertical non-stationary spatially variable seismic ground motions is crossed by an articulated high-speed train at several speeds. The spectral representation method is employed to generate the required number of acceleration time-history series at each support location of the railway viaduct studied. Wave passage, local soil conditions and loss of coherency effects have been accounted for in the simulated ground-motion time histories, with several peak ground accelerations. Train and bridge responses have been obtained by means of a non-linear dynamic interaction multibody and finite element model. An analysis of train running safety indices has been carried out. The properties of earthquakes and train speeds which may cause problems to traffic safety are detailed, as is the train derailment probability. The numerical simulation outcomes show that it is not safe for the train to travel over the studied viaduct in earthquakes with peak ground acceleration equal to 0.03 g and for train speeds above 280 km/h.

The evaluation of running safety of railway vehicles on viaducts requires the study of lateral dynamics for the coupled vehicle-bridge system. This includes the structural deformation of the bridge, the vehicle multibody dynamics, and the consideration of wheel to rail contact. In this work, a fully nonlinear coupled method for such study is presented. The model is developed in a modular way using finite element models for the structure and multibody dynamics models for the vehicles in an absolute reference, and implemented within an existing finite element commercial code. A key feature is the consideration of the kinematics and dynamics of nonlinear wheel to rail interface, considering elastic-frictional contact. This contact is based on a global geometric constraint between wheelset and track and tangential forces at local level of each contact point. Some elementary applications are presented for the behavior of the model for stable and unstable hunting motion when subjected to transient lateral loads such as a wind gust. These results show the relevance of considering nonlinear effects and in particular wheel to flange contact.

Currently, there is a growing concern about the conservation and maintenance of infrastructure. Within this context, bridges deserve special attention, given their technical complexity and strategic nature. To this end, modern technology provides the opportunity to implement systems for structural health monitoring (SHM), a field in which great advances have been made in recent years. In this sense, one of the fastest-growing lines of work in Civil Engineering is the early detection of incidents because of changes in the dynamic behaviour of structures. Throughout this paper, some of the most notable considerations that the authors have been appreciating in the latest structures studied are summarized. These may be of interest for the possible incorporation of dynamic parameters in SHM systems that could be implemented in other structures in the future. With this purpose, a review of the different issues that must be studied within the dynamic analysis of a structure is carried out, such as the structural typology, the type of instrumentation, the recorded accelerations, the analysis of the natural frequencies, the study of the modal damping ratio and the set of thresholds; issues that are also accompanied by examples observed in two real monitored structures.

This paper describes the principles, analysis and capacities of the axial-deck method developed in research on the optimization of the curved bridges directrices takin place at the UPM university in Madrid. The axial-deck method focuses on the two main structural challenges of curved cable-stayed bridges: the horizontal component of the load introduced by the stay cables on the deck; and the big torsion forces in the deck due to the unbalanced cable-stayed system. Hitherto, these problems have been addressed, either by optimizing the position of the tower and its geometric characteristics, or by modifying the morphology of the stay-cable system. Very little has been written about the possibilities of linking the structural behaviour to the deck directrix. This paper starts by describing the ideal solution equations, without considering the structure as statically indeterminate. Then, based on these equations, it follows the evolution of the method to a nonlinear iterative system. This evolution allows designs to be developed that consider the flexibility relation of all the structural systems involved in the problems. Finally, the method is validated with the redesign of two existing curved pedestrian bridges from prestigious engineering firms and the paper concludes with a structural behaviour analysis of all designs.

La seguridad de los puentes atirantados está basada principalmente en la resistencia de los cables y la posible fatiga de estos cables ha sido fuente de preocupaciones para los proyectistas e investigadores durante mucho tiempo. El principal objetivo de este artículo es el análisis de la importancia relativa de todos los factores que pueden producir fatiga en los cables: efectos estáticos y dinámicos de las sobrecargas de uso, irregularidades del pavimento, excitación paramétrica, presión aerodinámica del tráfico, desprendimiento de torbellinos y ráfagas de viento. Estos efectos han sido evaluados para un abanico amplio de puentes atirantados y extradosados que cubren la mayor parte de las aplicaciones actuales de esta tecnología. Este estudio demuestra que la tecnología actual de cables y las reglas de proyecto que se aplican ahora previenen la fatiga en los cables. Hay todavía un campo de mejora lo que permitiría reducir los costes de los cables pero esta reducción debería considerar la conjunción de algunos de los factores que se han considerado en este estudio, especialmente los efectos dinámicos de las cargas de servicio y el desprendimiento de torbellinos.