Andreas Andersson

Passive and Adaptive Damping Systems for Vibration Mitigation and Increased Fatigue Service Life of a Tied Arch Railway Bridge

In this paper, the use of external damping systems for vibration mitigation of railway bridge dynamics is studied. Theoretical analysis and numerical simulations are presented based on both passive and adaptive tuned mass dampers (TMD). Routines for a variable stiffness TMD in combination with incremental frequency estimates are developed and its performance under different loadings is studied. The potential of the dampers are studied on a tied arch railway bridge by means of numerical simulations. The bridge has earlier been the subject of extensive dynamic assessments and available field measurements of the response during train passage are reanalyzed and used for model calibration. Both field measurements and numerical simulations show resonant behavior of several hangers during train passage. Due to low structural damping, the resulting stresses are shown to significantly reduce the fatigue service life. A system of passive pendulum dampers was installed in 2005, proving an increased damping ratio due to free vibrations. Its performance during train passage was however not measured. The dynamic response is studied for different damping models based on a calibrated 3D finite element model. The response is highly sensitive to the train speed due to the risk of resonance. Fragility curves are adopted to estimate the extent of cumulative damage under mixed traffic loads at variable speeds.

Influence of the ballasted track on the dynamic properties of a truss railway bridge

This article presents numerical and experimental analyses of a steel truss railway bridge. The main feature of this work is that dynamic experiments have been performed before and after the ballasted track was placed on the bridge. Consequently, it has been possible to quantify the effect of the ballast and the rails on the dynamic properties of the bridge. For that, two finite element models, with and without the ballasted track, have been implemented and calibrated using the experimental results. It appears that the ballast gives an additional stiffness of about 25–30% for the lowest three eigenmodes. This additional stiffness can be only partly explained by the stiffness of the ballast. In fact, it seems that this additional stiffness is also due to a change in the support conditions.

Application of fluid viscous dampers to mitigate vibrations of high-speed railway bridges

ABSTRACT Several bridges along the Bothnia railway line in Sweden do not fulfil the Eurocode requirements regarding the maximum vertical bridge deck acceleration. The aim of this study is to investigate the possibility of reducing the acceleration of one of these bridges to an acceptable level by using post-installed viscous dampers. The bridge-damper system is described by a single-degree-of-freedom model. Assuming that the dampers do not change the mode shapes of the bridge, the model is further generalized to include higher order bending modes. The dampers are connected between the bottom surface of the bridge deck and the abutments. This creates an eccentricity between the connection point of the dampers and the neutral axis of the bridge, which is found to have a significant influence on the efficiency of the dampers. The results of this study also indicate that the proposed retrofit method can reduce the accelerations to an acceptable level.

Anomalous Nernst effect and heat transport by vortex vacancies in granular superconductors

We study the Nernst effect due to vortex motion in two-dimensional granular superconductors using simulations with Langevin or resistively shunted Josephson-junction dynamics. In particular, we sho ...

Modeling and simulations of quantum phase slips in ultrathin superconducting wires

We study quantum phase slips (QPS) in ultrathin superconducting wires. Starting from an effective one-dimensional microscopic model, which includes electromagnetic fluctuations, we map the problem ...

Influence of vortices and phase fluctuations on thermoelectric transport properties of superconductors in a magnetic field

We study heat transport and thermoelectric effects in two-dimensional superconductors in a magnetic field. These are modeled as granular Josephson-junction arrays, forming either regular or random ...

Scaling, finite size effects, and crossovers of the resistivity and current-voltage characteristics in two-dimensional superconductors

We revisit the scaling properties of the resistivity and the current-voltage characteristics at and below the Berezinskii-Kosterlitz-Thouless transition, both in zero and nonzero magnetic field. Th ...

Extending the fatigue service life of a railway bridge by local approaches

In this paper, fatigue assessment of a steel railway bridge is presented. The bridge is located in central Stockholm, Sweden, and is one of the most vital links for the railway network. The bridge ...

Load capacity assessment and strengthening of a railway arch bridge with backfill

In this paper, a load capacity assessment and strengthening measures of a multi-span railway arch bridge with backfill are presented. The bridge is located in Stockholm, Sweden, and constitute a vital link for the national railway network. The bridge consists of 20 concrete arches with overlying backfill, each with a span of 20 m. After more than 80 years of service, severe deterioration of the concrete was found during conditional assessments. A load capacity assessment was performed and the theoretical ultimate load was found to be highly dependent on the development of soil pressures along the arch barrel. The demands from the railway authority are to increase the allowable axle load from 22,5 to 25 tonnes and extend the service life by 50 years. Due to the uncertainties in structural behaviour and progressing degradation, extensive strengthening measures for the arch barrels were decided. To allow for full traffic at all times, the strengthening was performed in stages, to minimize any temporary reduction in load capacity due to removal of existing material. The strengthening was designed using non-linear finite element analysis and each stage of strengthening has been verified using in-situ field measurements.

Vibration mitigation of railway bridges using adaptive damping control

In this paper, the advantage of an adaptive damping system is presented. A damper with variable stiffness is tuned based on estimates of the real-time frequency response, facilitating optimal vibra ...