Distributed dynamic fibre-optic strain monitoring of the behaviour of a skewed masonry arch railway bridge

Sam Cocking,Haris Alexakis,Matthew Dejong

doi:10.1007/s13349-021-00493-w

Abstract

Skewed masonry arch railway bridges are common, yet their structural behaviour under typical working loads, along with gradual changes in behaviour due to degradation, can be difficult to determine. This paper aims to address this problem through detailed monitoring of a damaged, skewed masonry arch railway bridge in the UK, which was recently repaired. A comprehensive Structural Health Monitoring system was installed, including an array of fibre-optic Fibre Bragg Grating (FBG) sensors to provide distributed sensing data across a large portion of the bridge. This FBG monitoring data is used, in this paper, to investigate the typical dynamic structural response of the skewed bridge in detail, and to quantify the sensitivity of this response to a range of variables. It is observed that the dynamic bridge response is sensitive to the time of day, which is a proxy for passenger loading, to the train speed, and to temperature. It is also observed that the sensitivity of the response to these variables can be local, in that the response can differ throughout the bridge and be affected by existing local damage. Identifying these trends is important to distinguish additional damage from other effects. The results are also used to evaluate some typical assumptions regarding bridge behaviour, which may be of interest to asset engineers working with skewed masonry arch bridges.

Highlights

Masonry arch bridges feature significantly on the road and rail networks of the United Kingdom and other countries
Plots for the individual Fibre Bragg Grating (FBG) responses are arranged so that the direction of travel of the train is from the top to the bottom of the overall figure, with the train travelling directly above the FBGs in the left-hand column
After FBG L10, the fibre-optic cable returns westward along the centreline of the bridge, so that FBG L20 is the first to detect the passage of a train on the northern track and FBG L11 is the last

Summary

Introduction

Masonry arch bridges feature significantly on the road and rail networks of the United Kingdom and other countries. In the UK, roughly 40–50% of bridge spans on the rail and road networks are masonry arches, resulting in an approximate overall total of 70,000 of these structures [1] Many of these are located at important points on passenger and freight routes, meaning that their continued smooth operation carries considerable social and economic significance. The main signs of damage at this bridge are separation cracks between the brick arch barrel and stone spandrel walls, and an additional longitudinal crack in the south-eastern quadrant of the arch soffit This crack is located roughly underneath the centreline of the southern track and extends from the arch springing by just over 3 m, approximately following the skewed span direction. In 2016, soil anchors were fitted in these wing walls, ten new tie rods were installed through the spandrel walls to constrain the arch in its transverse direction, and the cracks were comprehensively stitched using steel

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Conclusion