Interaction between surface structures and tunnelling in sand: Centrifuge and computational modelling

Tunnelling in urban areas requires a careful estimation of the consequence of soil settlements on existing buildings. In this paper the interaction between the excavation of a tunnel in sand and surface structures is investigated. A two dimensional finite element model is presented and validated through comparison with centrifuge test results, both with and without structures. The model is then used to perform a sensitivity study on the effect of building weight on soil movements and structural deformations. The results of the validation indicate that assuming a no-tension interface between the soil and the structure is essential to capture the soil-structure interaction that was experimentally observed. The parametric analyses show that the relation between the building stiffness and the tunnelling-induced deformations depends on the building weight.Financial support was provided by the Engineering and Physical Sciences Research Council of the United Kingdom, under grant reference number EP/K018221/1.This is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.tust.2015.07.01

Centrifuge investigation comparing the rocking response of two soil-structure systems

Seismic protection of structures by means of rocking isolation is becoming increasingly popular, because allowing uplift is an inexpensive way to reduce structural demand. However, understanding the role of soil–structure interaction in the response of rocking systems is important to define what type of rocking system might be most effective. To address this challenge, a campaign based on centrifuge modelling and testing is currently ongoing. The primary objective is to assess the force demand that rocking systems experience during their motion. Flexible structures that rock while stepping on discrete footings (structural rocking) and flexible structures with discrete footings rocking on soil (foundation rocking) are both considered. Following this distinction, two building models were designed with the only difference being the connectivity of the columns to the footings. For structural rocking, columns were designed to detach and step on their footings, while for foundation rocking the footing-column connection was designed to be rigid. The two building models were tested side-by-side in a centrifuge. A second test was also conducted, where thin steel “fuses” were installed in the interface of structural rocking, to further study the allocation of energy dissipation between structural elements and fuses, and soil medium. The building models were placed on the surface of dense sand and then tested using sinusoidal ground motions which caused a combination of sliding and rocking. The global response of the models in terms of overturning moment and storey shear was investigated and back validated by obtaining directly the internal loads, which were found capped regardless of the extent of rotation. More-over, the base isolation effect was evident during large amplitude resonant excitations, whereas during a low frequency low amplitude excitation there was no clear benefit of rocking. Finally, no significant effect was observed in limiting the base shear demand by using the steel fuses

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

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

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

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

Discussion of “A cantilever approach to estimate bending stiffness of buildings affected by tunnelling” by Twana Kamal Haji, Alec M. Marshall, and Walid Tizani

This discussion considers the procedure proposed by Haji, Marshall and Tizani for the assessment of the structural stiffness of frame structures subjected to tunnelling. The discussion focuses on the potential contribution of both shear and bending flexibilities to the response of frame structures to tunnelling, as well as the role of the foundation scheme on the boundary conditions at the base of the structure. The validity of applying the proposed set of equations within currently available methods of prediction of tunnelling-induced deformations, based on modification factors, is also discussed

Vibration modes and equivalent models for flexible rocking structures

Predicting the displacement and force response of flexible rocking structures to ground motion is important for their assessment and design. Insofar as practical, it is desirable to use simple mechanical models to make these predictions. However, the complex coupling between rocking and vibration makes accurate predictions with simple models difficult. In this paper, the use of semi-coupled equivalent models to approximate the dynamic response of multi-mass structures rocking on rigid ground is evaluated. These equivalent models feature a two-degree of freedom coupled rocking oscillator to describe the interaction of rocking and the first mode of vibration, and uncoupled linear elastic oscillators to describe higher mode vibration response. To evaluate these equivalent models, the modal components of the dynamic response of multi-mass structures are first determined. These components highlight the critical influence of the excitation of vibration modes at impact. Then, further investigations are carried out by comparing equivalent model simulations to recent shake table tests and multi-mass analytical model simulations. These comparisons reveal that the equivalent models can capture the rocking response accurately for a realistic range of displacements, if a new ground acceleration scaling term is adopted. However, the uncoupled linear elastic oscillators do not consider excitation at impact and consequently, the equivalent models do not capture the acceleration response adequately. Therefore, on the basis of the analytically identified modal components, a further modification that improves the equivalent model acceleration predictions is proposed and validated.The first author would like to express gratitude for funding from Trinity College, Cambridge Overseas Trust and the Suna and Inan Kirac Foundation