36 research outputs found

    A lightweight Transformerā€based neural network for largeā€scale masonry arch bridge point cloud segmentation

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    Transformer architecture based on the attention mechanism achieves impressive results in natural language processing (NLP) tasks. This paper transfers the successful experience to a 3D point cloud segmentation task. Inspired by newly proposed 3D Transformer neural networks, this paper introduces a new Transformer-based module, which is called Local Geo-Transformer. To alleviate the heavy memory consumption of the original Transformer, Local Geo-Transformer only performs the attention mechanism in local regions. It is designed to mitigate the information loss caused by the subsampling of point clouds for segmentation. Global Geo-Transformer is proposed to exploit the global relationships between features with the lowest resolution. The new architecture is validated on a masonry bridge dataset developed by the authors for their earlier work on a previous segmentation network called BridgeNet. The new version of the network with Transformer architecture, BridgeNetv2, outperforms BridgeNet in all metrics. BridgeNetv2 is also shown to be lightweight and memory efficient, well-adapted to large-scale point cloud segmentation tasks in civilĀ engineering

    The dynamic behaviour of flexible oscillators rocking and sliding on concentrated springs

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    This study presents the Flexible Rocking Model on Concentrated Springs (FRMCS), developed to investigate 2D laterally flexible oscillators rocking and sliding on deformable support media during ground excitations. In this model, concentrated vertical springs and viscous dampers simulate the contact forces from support medium at the corners of the body; the tensionless vertical contact element is linear in compression. Horizontal concentrated springs and linear viscous dampers simulate the frictional behaviour at the corners; the constitutive law for the springs models elastic deformations and sliding (according to Coulomb's friction law). With these elements, FRMCS can model the response of a rocking body which can experience sliding and freeā€flight phases of motion. The consideration of the flexibility of the support medium enables the evaluation of the forces exerted by the support medium on the structure during an impact. In this study, the FRMCS response is first compared to a previous model where the support medium deformability and the effects of sliding and freeā€flight are ignored. Then, the responses of four configurations, which feature either stiff or soft lateral springs and stiff or soft highā€grip support media, are examined under the influence of pulse excitations. Finally, to understand the potential influence of sliding, a configuration with a lowā€grip support medium is explored. The comparative influence of lateral flexibility and support medium deformability and sliding is quantified with stability diagrams and various response spectra, describing structural force and moment demands

    Evaluation of the response of a vaulted masonry structure to differential settlements using point cloud data and limit analyses

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    Differential settlements have adverse effects on the serviceability and stability of vaulted masonry structures. However, the existing monitoring and assessment techniques do not capture these effects in sufficient detail. In this paper, a new approach is proposed to better describe the influence of support movements on barrel vaults. In this approach, laser scan point clouds of a settling vaulted structure are compared. Different cloud comparison methods are used to accurately identify the displacements of small point cloud segments. In particular, a new cloud comparison method, which modifies the well-known iterative closest point (ICP) registration algorithm, is developed. By constraining ICP to ensure displacement continuity between adjoining point cloud segments, three dimensional movement estimates of the structure are obtained. These estimates delineate the settlement response by indicating the location and magnitude of cracking. This rich information is then used to identify the settlement response mechanism of the vault using limit state numerical analysis. Finally, by interpreting the numerical results with relevant serviceability criteria, a new method to quantify the influence of settlements on barrel vaulted masonry structures is proposed. This damage assessment technique is used to evaluate observed damage due to piling-induced settlements in a masonry viaduct at London Bridge Station.The work carried out was funded by EPSRC and Innovate UK, through the Cambridge Centre for Smart Infrastructure and Construction (Grant Reference Number EP/L010917/1)

    Masonry buildings subjected to settlements: half-scale testing, detailed measurements, and insights into behaviour

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    Industry procedures to assess the risk of settlement-induced damage to masonry buildings ignore key aspects of the problem, such as the influences of building weight, faƧade openings, and floor structures. Experimental data are needed to characterise the influence of these aspects on damage. This paper describes tests on three brick masonry half-scale building models subjected to settlements. The use of scaling rules in choosing the model materials and kentledge, the settlement apparatus, and the cross-validation of displacement and strain measurements are presented. Comparative evaluation of building responses show that: (i) the distribution of building weight and the resulting in-situ stresses play a key role in determining compliance to settlements, (ii) openings make the structure vulnerable to cracking and (iii) floor slabs stiffen and strengthen the building and prevent the formation of damage in the upper floors, leading to a concentration of damage at the ground storey

    Determination of free vibration properties of masonry arch bridges using the dynamic stiffness method

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    Masonry arch bridges constitute over half of the European bridge stock. The dynamic response of these bridges to traffic loads is influenced by their free vibration properties, i.e. their natural vibration frequencies and mode shapes. However, these properties have not been systematically examined to date. This paper utilises the dynamic stiffness method (DSM) to obtain an improved fundamental understanding of the free vibration properties of idealised single and multi-span arch bridges. In this approach, the piers and arches are modelled as an assembly of linear Timoshenko beam segments, the backing and infill are represented with axial struts and the underlying soil with concentrated spring elements. These idealisations enable rapid but accurate calculations of in-plane free vibration properties. To demonstrate this, the proposed procedure is applied to a simply-supported arch structure, a small-scale single-span arch bridge model and a multi-span arch bridge, where published experimental data is available. Then, free vibration analyses of representative single and multi-span arch bridges are performed. The results obtained from DSM analyses agree with detailed 3D finite element models and reveal the critical influence of backing elements and the interactions between adjacent spans on free vibration properties. Lastly, a range of arch bridge geometries are examined to reveal the shortcomings of existing provisions for modal frequency estimation in codes of guidance

    Dynamic amplification in masonry arch railway bridges

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    Dynamic amplification of loads in masonry arch&nbsp;railway bridges&nbsp;is not well understood. There is a scarcity of experimental data and previous numerical studies have only addressed a few specific bridge geometries. Despite this, guidance documents provide empirical and unvalidated formulae to calculate dynamic amplification for masonry arch railway bridges. To improve our fundamental understanding of the problem, determine appropriate modelling strategies and evaluate the reliability of guidance documents, simple 2D and 3D models are explored in this paper. The 2D approach idealises key bridge components (pier, arch, fill and backing elements) with straight Timoshenko beams, springs and&nbsp;lumped masses. It uses an analytical&nbsp;dynamic stiffness&nbsp;formulation, which is computationally efficient and well-suited to explore a range of bridge models. The higher fidelity 3D modelling approach uses shell and solid finite elements and is used to evaluate the limitations of 2D models. In both approaches, linear-elastic&nbsp;material behaviour&nbsp;is assumed and train loads are idealised as moving vertical loads distributed over an effective area. The modelling results indicate a complex relationship between train speed and dynamic amplification that depends critically on bridge geometry and axle spacing. In general, the multi-span bridge configurations experienced higher dynamic amplification over operational train speeds. The results also higlight deficiencies in existing code provisions and demonstrates how efficient numerical models may replace these provisions.</p

    The influence of impact modelling assumptions on the dynamic behaviour of flexible rocking oscillators

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    For rigid rocking models, energy dissipation relies solely on impact. Consequently, the position of the impulse acting on the rocking body determines the magnitude of energy loss and strongly influences the subsequent dynamic response. This paper evaluates the corresponding influence of the location of the vertical impulse on the dynamic behaviour of flexible rocking oscillators. The dynamic behaviour of a rocking flexible oscillator is explored in this study with an impact model that parametrically considers the position of impulse. The influence of the position of impulse on the expected energy loss during impact, and on the overturning stability of the flexible rocking oscillator are then examined. It is shown that the energy loss at impact reduces and the potential for overturning instability increases, for impulses located at increasing distances from the future rocking corner
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