Sensing dynamic displacements in masonry rail bridges using 2D digital image correlation

Dynamic displacement measurements provide useful information for the assessment of masonry rail bridges, which constitute a significant part of the bridge stock in the UK and Europe. Commercial 2D Digital Image Correlation (DIC) techniques are well suited for this purpose. These systems provide precise non-contact displacement measurements simultaneously at many locations of the bridge with an easily configured camera setup. However, various sources of errors can affect the resolution, repeatability and accuracy of DIC field measurements. Typically, these errors are application specific and are not automatically corrected by commercial software. To address this limitation, this paper presents a survey of relevant DIC errors and discusses methods to minimise the influence of these errors during equipment setup and data processing. A case study application of DIC for multi-point displacement measurement of a masonry viaduct in Leeds is then described, where potential errors due to lighting changes, image texture and camera movements are minimised with an appropriate setup. Pixel-metric scaling errors are kept to a minimum with the use of a calibration method which utilises vanishing points in the image. However, comparisons of DIC relative displacement measurements to complementary strain measurements from the bridge demonstrate that other errors may have significant influence on the DIC measurement accuracy. Therefore the influence of measurement errors due to lens radial distortion and out of plane movements are quantified theoretically with pinhole camera and division distortion models. A method to correct for errors due to potential out of plane movements is then proposed

The importance of modelling assumptions when analysing the dynamic response of a masonry railway viaduct

© 2018 The International Masonry Society (IMS). The masonry viaduct at Marsh Lane is an important part of the railway network near Leeds, UK, dating from the 1860s. However, deterioration has resulted in notable deflections under train loads, which have concerned asset managers. Coupled with uncertainty regarding the true structural behaviour under serviceability conditions, this has led to detailed monitoring of the viaduct. This paper summarises the main conclusions of the monitoring installation before focusing on the evaluation of computational modelling of the viaduct, through comparison of modelling and monitoring results. In the monitoring scheme, fibre-optic cables containing Fibre-Bragg Gratings allowed measurement of dynamic in-plane barrel strains while digital image correlation captured displacements using commercial video cameras. The results illuminated a complicated three-dimensional dynamic response under train loading and highlighted the importance of interaction between adjacent spans. Separately, rail loading of the viaduct was simulated with a series of finite element models, each with increasing levels of complexity, to establish the relative stiffness contributions of various structural components. These models were then compared to detailed measurements from the real viaduct so that their validity could be evaluated. This approach revealed the impact of some common modelling assumptions and permitted assessment of nonlinear contributions to structural behaviour

The effects of wind on the loading and vibration of stone pinnacles

© 2016 International Masonry Society. All rights reserved. Following the collapse of a tympanum pinnacle at Beverley Minster in Yorkshire, a research project was undertaken to investigate the wind forces which act on stone pinnacles. A survey was conducted and the most common failure modes were identified, which highlighted the importance of dynamic forces in addition to the static drag force. Further, the potential impact of decorative crockets on these forces was of interest. Both static and dynamic forces on pinnacles were investigated through a series of wind tunnel tests. The results demonstrate the relative magnitude of these forces, and that the decorative crockets do appreciably affect both the drag force and wind-induced vibration. The experimental data was used to derive general relationships for wind forces acting on stone pinnacles for potential use in engineering practice

Experimental Identification of the Dynamic Characteristics of a Flexible Rocking Structure

This paper presents the results of free vibration and earthquake excitation tests to investigate the dynamic behaviour of freely rocking flexible structures with different geometric and vibration characteristics. The primary objective of these tests was to identify the complex interaction of elasticity and rocking and discuss its salient effects on the rocking and vibration mode frequencies, shapes and excitation mechanisms. The variability of response is discussed, including critical investigation of the repeatability of the tests. It was found that the variability in energy dissipation and energy transfer to vibrations at impact may lead to significantly different responses to almost identical excitations.The first author would like to thank Trinity College, Cambridge Overseas Trusts, Suna and Inan Kirac Foundation, University of Auckland and University of Canterbury for their financial and academic support.This is the author accepted manuscript. The final version is available from Taylor & Francis via http://dx.doi.org/10.1080/13632469.2016.113816

Dynamic response of a damaged masonry rail viaduct: Measurement and interpretation

Despite recent advances in modelling and testing techniques, assessing the serviceability of ageing masonry rail bridges remains a significant challenge. Most assessment methods are based on ultimate strength, while reliable measurement-based assessment criteria are lacking. This paper aims to improve the understanding of serviceability behaviour through detailed dynamic monitoring of the bridge locally (e.g. in locations of damage) and globally (e.g. interaction of different components). Quasi distributed sensing techniques (Fibre Bragg Grating cables and Digital Image Correlation) were used to quantify the bridge dynamic response through extensive measurement of strains and displacements. Specifically, these techniques were applied to two damaged spans of the Marsh Lane viaduct in Leeds, UK. A detailed investigation of the dynamic pier and arch barrel movements reveal how the response mechanisms relate to, and likely propagate, the existing damage. For instance, rotation of piers in the bridge longitudinal plane causes significant span opening and closing, which in turn causes the skewbacks and backing to rock on the piers. This is accompanied by flexural deformation of the arch, which forces the existing transverse cracks to experience high compressive strains. Similarly, the transverse rotation of piers due to the presence of the relieving arches causes spreading of the relieving arches and opening of the longitudinal crack above. These observations provide new insight into behaviour and lead to suggestions for improving assessment techniques for masonry viaducts

Structural health monitoring of a masonry viaduct with Fibre Bragg Grating sensors

The Marsh Lane viaduct is a masonry railway bridge constructed during the 19th century nearby Leeds Central Railway Station. The bridge appears significantly damaged due to the increase of the operational train loads over the last decades and due to environmental effects. Due to this degradation, extensive repair was conducted in 2015. After this repair work, an extensive fibre optic sensor network was installed below three spans of the bridge to monitor surface strains at 68 locations on the underside of the arch spans. The paper compares data collected from two monitoring periods, 16 months apart. Combining statistical analysis and signal processing techniques, the results show that local damage, as well as change in the global dynamic behaviour of the structure over time, can be effectively detected with the use of Fibre Bragg Grating sensors.This work is being funded by the Lloyd’s Register Foundation, EPSRC and Innovate UK through the Data-Centric Engineering programme of the Alan Turing Institute and through the Cambridge Centre for Smart Infrastructure and Construction (CSIC). Funding for the monitoring installation was provided by EPSRC under the Ref. EP/N021614/1 grant and by Innovate UK under the Ref. 920035 grant

A multi-sensing monitoring system to study deterioration of a railway bridge

This study presents a multi-sensing monitoring system recently installed in a Victorian railway viaduct in Leeds, UK. The viaduct is in continuous use since its construction during the 19th century and suffers extensive cracking due to the combined action of increased train loads and environmental effects. The bridge was retrofitted in 2015 and there was the need to assess the effectiveness of the intervention and better understand the ongoing deterioration process. For this reason, a multi-sensing system was designed that comprises a fibre Bragg grating network to measure distributed dynamic deformation across three arch spans of the bridge, acoustic emission sensors to detect rates of cracking, and high sensitivity accelerometers to study the dynamic response at critical locations. The system is self-sustaining, self-powered and remotely controlled, and uses an algorithm that combines information from the three different types of sensors to track variations of response parameters of the bridge over time.This work is being funded by the Lloyd’s Register Foundation, EPSRC and Innovate UK through the Data-Centric Engineering programme of the Alan Turing Institute and through the Cambridge Centre for Smart Infrastructure and Construction. Funding for the monitoring installation was provided by EPSRC under the Ref. EP/N021614/1 grant and by Innovate UK under the Ref. 920035 grant

The Marsh Lane Railway Viaduct: 2 Years of Monitoring with Combined Sensing and Surveying Technologies

Marsh Lane viaduct is a typical example of a 19th century brick masonry railway arch in the UK. It frequently carries passenger trains to and from Leeds Station. This paper broadly discusses the sensing techniques and associated analysis procedures used to (i) identify the reasons for existing damage, (ii) quantify their impact on the dynamic response of the structure and (iii) measure degradation of the response over a period of one year. To identify existing damage, distortions in geometry of the structure are examined with new point cloud processing techniques. With the aid of limit analyses, these distortions are interpreted, and past support movements which may have caused the distortions are identified. Then, to measure the dynamic response of the bridge, quasi-distributed fibre optic strain sensing and digital image correlation displacement measurement techniques are used. These highlight the increased dynamic response around locations of existing damage, and point out to the global mechanisms of response that could propagate damage. Continuous fibre optic strain measurements between November 2017 and 2018 are then discussed to investigate the ongoing deterioration.This work is being funded by the Lloyd’s Register Foundation, EPSRC and Innovate UK through the Data-Centric Engineering programme of the Alan Turing Institute and through the Cambridge Centre for Smart Infrastructure and Construction. Funding for the monitoring installation was provided by EPSRC under the Ref. EP/N021614/1 grant and by Innovate UK under the Ref. 920035 grant

Evaluating the Application of Microbial Induced Calcite Precipitation Technique to Stabilize Expansive Soils

Expansive soils, also known as swell-shrink soils have been a problem for civil infrastructures including roads and foundations from ancient times. The use of chemical additives such as cement and lime to stabilize expansive soils is a common practice among geotechnical engineers, especially for lightly loaded structures. However, several occurrences of subgrade failures have been observed after stabilizing with chemical additives. Hence, engineers are in search of sustainable stabilization alternatives. Microbial Induced Calcite Precipitation (MICP) is gaining attention as an environmentally friendly soil improvement technique. Several researchers have successfully tested its feasibility in mitigating liquefaction-induced problems in sandy soils. In this research, the authors are evaluating its effectiveness in stabilizing expansive soils. For this purpose two natural expansive soils with high and low plasticity properties were subjected to MICP treatments. The soil samples were first augmented with bacterium Sporosarcina Pasteurii and then treated with Calcium Chloride and Urea. Variables such as microbial concentrations and curing times were studied in this research. Geotechnical testing including Atterberg limits and unconfined compression strength were performed to evaluate the efficacy of MICP treatments. Preliminary results indicate that there is a reduction in plasticity and swelling characteristics of the soils and increase in the unconfined compression strength