Railway transition zones present a major challenge in railway track design mainly due to abrupt jumps in stiffness and differential settlements that result from crossing stiffer structures such as bridges or culverts. Despite numerous efforts to mitigate these transition effects at both the superstructure and substructure levels, a comprehensive solution remains elusive. Substructure-level interventions have demonstrated some effectiveness but are often cost-prohibitive and challenging to implement in existing operational railway transition zones. In contrast, mitigation measures at the superstructure (rail, sleepers, rail-pads, under-sleeper pads) level can be easily installed but have shown limited improvement in site measurements. This study evaluates the influence of different sleeper configurations in transition zones and reduced sleeper spacings on the operation-driven dynamic amplifications in railway transition zones, employing a recently proposed criterion based on the total strain energy in the track-bed layers (ballast, embankment, and subgrade). In addition to this, the influence of the loss of contact between sleepers and ballast (i.e., hanging sleepers), which typically results from the differential settlement, is studied. The first part of the paper provides useful insights regarding the interventions (and/or initial design) in the sleeper configuration and spacing, whereas the second part of the work highlights the need for interventions to deal with the loss of contact between sleeper and ballast. A 2-dimensional finite element model of an embankment-bridge transition was used for the analysis. The results show that it is not possible to mitigate the transition effects completely using the interventions involving sleeper spacing and configuration.@en

Railway transition zones are critical regions in railway infrastructure that are subjected to excessive operation-driven degradation due to energy concentration within these zones. This work presents a heuristic approach to optimise the geometry of the transition structure and investigate its influence on the strain energy distribution in the railway transition zones (RTZs), with a specific focus on embankment-bridge transitions equipped with a newly proposed ’Safe Hull-Inspired Energy Limiting Design (SHIELD)’ transition structure. For this purpose, a number of three-dimensional finite element models are used to analyze different geometric profiles of SHIELD in a systematic manner. By altering SHIELD's geometry across longitudinal, transversal, and vertical directions, the influence of the different geometric profiles on the total strain energy distribution across the trackbed layers (ballast, embankment, and subgrade) is studied in terms of spatial and temporal variations. The results establish the contribution of geometry to energy redistribution in all three directions and present an optimum geometry for the type of transition under study. It is found that among all the profiles, the longitudinal geometric profile of SHIELD has the most significant impact on the strain energy distribution, while the transversal profile primarily influences the ballast layer, and the alteration of vertical profiles enhance the local redistribution of strain energy in the vicinity of the transition interface. The preliminary optimisation (heuristic approach) presented in this work provides the starting point for full-scale optimisation to obtain tailored shapes of transition structures such that there is neither a concentration of energy nor an obstruction in the flow of energy in RTZs.@en

Railway transition zones (RTZs) are regions where abrupt track stiffness changes occur that may lead to dynamic amplifications and subsequent track deterioration. The design challenges for these zones arise due to variations in material properties in both the depth (trackbed layers composed of different materials) and longitudinal directions of the track, as well as temporal variations in mechanical properties of materials due to several external factors over the operational period. This research aims to investigate the effects of these variations in material properties (i.e., of the resulting stiffness distributions in vertical and longitudinal directions) on the behaviour of RTZs, assess from this perspective the performance of a novel transition structure called the SHIELD, and establish a methodology for designing a robust solution to mitigate the dynamic amplifications in these zones. Results indicate that stiffness variations in both vertical and longitudinal directions significantly influence the dynamic behaviour of the RTZs. The study also suggests a permissible range of stiffness ratios to control the amplification of strain energy in the most critical components of RTZs, both in the initial state as well as during the operational phase (where material properties may vary over time). Moreover, the proposed methodology offers a valuable tool for the design and evaluation of RTZs and is applicable to various transition types and a broad spectrum of material properties.@en

Railway transition zones are the most critical part of the railway infrastructures that experience 4-8 times more degradation compared to open tracks. Despite several attempts to reduce the maintenance and operation costs in these critical zones, a robust and comprehensive solution remains unknown. In recent studies, a robust safe hull inspired energy limiting design of a transition structure was proposed for an embankment-bridge transition (without ballast layer over the bridge) to deal with operation-induced degradation. However, this solution was investigated in detail for only this particular type of transition. In this work, the scope of this mitigation measure is extended for an embankment-bridge transition with ballast running over the bridge and its performance is evaluated using a strain-energy criterion. It was concluded in the end that the safe hull inspired energy limiting design can effectively mitigate the operation-induced dynamic amplification for more than one type of railway transition zones. @en

Railway transition zones (RTZs) experience higher rates of degradation compared to open tracks, which leads to increased maintenance costs and reduced availability. Despite existing literature on railway track assessment and maintenance, effective design solutions for RTZs are still limited. Therefore, a robust design criterion is required to develop effective solutions. This paper presents a two-step approach for the formulation of a preliminary-design criterion to delay the onset of processes leading to uneven track geometry in RTZs. Firstly, a systematic analysis of each track component in a RTZ is performed by examining spatial and temporal variations in kinematic responses, stresses and energies using a finite element model of an embankment-bridge transition. Secondly, the study proposes an energy-based criterion to be assessed using a model with linear elastic material behavior and states that an amplification in the total train energy in the proximity of the transition interface is an indicator of increased (and thus non-uniform) degradation in RTZs compared to the open tracks. The correlation between the total strain energy (assessed in the model with linear material behaviour) and the permanent irreversible deformations is demonstrated using a model with non-linear elastoplastic material behavior of the ballast layer. In the end, it is claimed that minimising the magnitude of total strain energy will lead to reduced degradation and a uniform distribution of total strain energy in each trackbed layer along the longitudinal direction of the track will ensure uniformity in the track geometry.@en

The railway transition zone where the track transitions from a ballasted track to a slab track, is a crucial area that can experience amplified dynamic responses. This work aims to develop a deeper insight into the mechanisms leading to the amplified dynamic response in railway transition zones. The study employs a finite element model to investigate the amplification of total strain energy due to the phenomena of reflection and redistribution of energy close to the transition interface. The results of the study are obtained for three case studies involving non-reflecting boundary (representing an energy sink) and homogeneous material along the vertical direction of the track, and the responses are studied for individual and combined effects in comparison to a benchmark case. The findings of the study show that eliminating the phenomena results in no dynamic amplification in total strain energy in railway transition zones. The conclusion highlights the importance of understanding these phenomena in order to design an efficient railway transition structure.@en

ransition zones in railway tracks experience strong amplification of stress and strain fields due to the passage of train over inhomogeneity. The inhomogeneity in these zones can be attributed to changes in mechanical properties of material along the longitudinal direction of the track, and to displacement/traction discontinuities at interfaces leading to an amplified response in railway transition zones (TZ) with respect to the open tracks. In this paper, different kinds of inhomogeneities are considered in isolation and in combination to study the effects on railway track components in transition zone. The first type of inhomogeneity considered is non-uniformity of materials at various levels of the track along the longitudinal direction. The second type of inhomogeneity that will be considered arises from displacement and traction discontinuities at the interface of soil and structure and at the interface of sleepers and ballast (hanging sleepers). The results provide necessary insight for the design of effective mitigation measures to prevent the amplified response in railway TZ.@en

This comprehensive study addresses the persistent issue of railway transition zone degradation, evaluating the efficacy of the most commonly used mitigation measures and proposing a novel Safe Hull-Inspired Energy Limiting Design (SHIELD) of a transition structure. Firstly, this work assesses the traditional transition structures, including horizontal and inclined approach slabs and transition wedges, using commonly studied responses (kinematic response and stress) and a recently proposed criterion based on total strain energy minimization. The second part of the paper evaluates the newly introduced transition structuress (SHIELD) using the same criterion as used for the evaluation of the traditional transition structures. A detailed investigation of existing and a new design using a 2-dimensional finite element model shows SHIELD’s effectiveness in managing energy flow at transition zones and provides reasoning behind the ineffectiveness of the other commonly used transition structures. The study demonstrates the robustness and comprehensiveness of the recently developed energy-based criterion and its applicability to different types of transition zones. Moreover, it highlights the potential of SHIELD as a solution to address the complexities associated with the design of railway transition zones.@en

This paper studies the effectiveness of adding auxiliary rails as a mitigation measure for degradation in transition zones of railway tracks. More specifically, it investigates the settlement mechanisms counteracted by the additional rails. Results show that when the system’s response is in the quasi-static regime, adding auxiliary rails over the soft part of the transition zone is beneficial while adding them over the whole transition zone is not. Furthermore, the auxiliary rails have a beneficial impact also when the system’s response is in the dynamic regime; the beneficial effect is caused by the improved load distribution to the supporting structure and not from counteracting the dynamic response amplification that occurs at transition zones. While this mitigation measure has been previously investigated, the contribution of this study lies in a more in-depth analysis of the mechanism through which auxiliary rails can mitigate the degradation at transition zones.@en

This work presents a numerical simulation of the church of San Francesco, Amatrice, and subsequent interpretation of the evolution of damage and collapse mechanisms that were caused by the main events of the seismic sequence that hit the Apennine area of Central Italy in 2016. The study primarily focuses on the response of the church with reference to the two main events: seismic shocks of 24th August and 30th October 2016. The dynamic non-linear analysis was performed on the structure using Abaqus CAE 2017, which was intended at simulating the damage and collapse that were observed on the real structure subsequent to the main seismic events. The study also contributes to suggest preventive interventions/material enhancements that could have either limited or mitigated the damage, thereby avoiding the collapse of the Church. In an effort to reciprocate the seismic events, the time-history of the accelerograms recorded at the AMT fixed station and of the amplified local accelerogram were considered as seismic input. Furthermore, this study presents simulations of the response of the structure subjected to the main seismic events simulated in a continuous chronological sequence and the effects of local and global interventions on the seismic response of the entire structure. This study indicates the application of numerical simulation as an efficient tool for seismic analysis of masonry structures, with the obtained results ranging within the acceptable margin of errors. In addition, the simulations can be used to analyse the proposed interventions, while taking into account the limitations of the software and computational techniques. This paper highlights the interesting conclusions related to the effects of local and global interventions in case of the church of San Francesco and the role of amplification of the accelerations for the site of Amatrice.@en

The problem of seismic safety assessment is discussed with reference to the case of an historical reinforced concrete bridge; specifically, a bridge located in Songavazzo, Italy across the Valeggia river, completed in 1911. Experimental testing has been performed, providing all the required information for the identification of the dynamic behaviour. Seismic vulnerability has been evaluated with both response spectrum modal analyses and nonlinear static (push-over) analyses as well. The bridge response is compared to the one obtained for a similar bridge yet reflecting a different structural scheme. Structural analyses have allowed to highlight different structural concepts while, on the other hand, they show the complementary nature of the two bridges. In both cases, reinforced concrete arches are mainly subjected to axial loads and provide the main structural system.@en

This paper presents a discussion on the experimental results of the compression tests performed on full-scale fire-exposed, Reinforced Concrete-Filled Steel Tubes (RCFST) and Reinforced Concrete (RC) short columns (outer diameter 457 mm and length 1600 mm). In the companion papers, full details about the test procedure, thermal field, load-displacement curves are provided. In particular, the domain of research work includes the results of five tests for thermal field measurements, that consider four specimens heated in a gas furnace in standard fire conditions (ISO 834), one specimen heated in an electric furnace in non-standard conditions and the results of six axial compressive tests. In this paper, the results of residual compression tests are discussed and an analytical-experimental comparison is proposed. The work concludes with main remarks about the experimental results.@en

This work is aimed at the numerical interpretation of the evolution of damage and collapses observed on the Civic Tower of Amatrice, caused by the main events of the seismic sequence of 2016 in the Apennine area of Central Italy. In particular, the study considers the response of the tower with reference to the two main events, occurred on August 24th and October 30th, 2016 respectively. Non-linear dynamic analyses were carried out by developing a finite element model and the behaviour of the tower was investigated with reference to the damage and partial collapses produced by the main events. In dynamic numerical analyses, the accelerograms corresponding to the main seismic events obtained with the study of the site effects were used as seismic input. Moreover, studies have been carried out to understand if and which of the interventions of reinforcement/seismic improvement, realized at the beginning of the years ‘80, have been determinant to limit the damage, avoiding the complete collapse of the tower. The results of the study, on the one hand, allow to highlight a good correspondence between the evolution of the actual damage observed on the tower and the damage assessed by numerical analyses thus demonstrating the validity of the numerical models set up for the analyses. On the other hand, however, they have made it possible to underline how the presence of the improved material and structural reinforcement interventions carried out at the beginning of the years ‘80 have contributed to avoid the complete collapse of the tower.@en