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  • ItemOpen AccessAccepted version Peer-reviewed
    Monitoring, Modeling, and Assessment of a Self-Sensing Railway Bridge during Construction
    (American Society of Civil Engineers (ASCE), 2018) Butler, LJ; Lin, W; Xu, J; Gibbons, N; Elshafie, MZEB; Middleton, CR; Butler, Liam [0000-0002-4244-5142]; Gibbons, Niamh [0000-0001-5140-4441]; Elshafie, Mohammed [0000-0001-9908-5515]; Middleton, Campbell [0000-0002-9672-0680]
    This study demonstrates how integrating fibre optic sensor (FOS) networks into bridges during their construction can be used to quantify their pre-service performance. Details of the installation of a large FOS network on a new steel-concrete composite railway bridge are presented. An overview of the FOS technology, installation techniques, and monitoring program is presented and the monitoring results from several construction stages are discussed. A finite element (FE) model was developed and a phased analysis was carried out to simulate strain development in the bridge during consecutive construction stages. The response of the self-sensing bridge to the time dependent properties of the concrete deck was evaluated by comparing FOS measurements to predicted results based on several model code formulations (Eurocode 2, ACI 209, and CEB-fip) implemented in the FE model. Pre-service strain distribution due to dead loading is typically assumed to act uniformly along the bridges' span, however the monitoring results revealed these to be highly variable as a result of the complex interaction between gravity loading, bridge geometry, time-dependent concrete properties and temperature effects. Moment utilisation of the main steel girders and transverse composite beams at their pre-service condition was assessed and found to be between 19.3% and 24.9% of their design section capacities. Quantifying pre-service performance of bridges via integrated sensing also establishes a well-defined baseline which enables future data-driven condition assessment.
  • ItemOpen AccessAccepted version Peer-reviewed
    Rationalising assessment approaches for masonry arch bridges
    (Thomas Telford Ltd., 2012-09) Gibbons, Niamh; Fanning, Paul J; Gibbons, Niamh [0000-0001-5140-4441]
    Masonry arch bridges, most of which have far exceeded modern design lives, have demonstrated themselves to be sustainable structures with low life-cycle costs. However, increased traffic loading and material deterioration over time necessitate periodic reassessment of these structures. There are numerous different analytical methods available for the assessment of masonry arch bridges. The expectation is that for increasing levels of assessment complexity an increase in load capacity converging on the ultimate capacity would be achieved. In this paper it is demonstrated that this is not always the case. This has cost implications for both the bridge assessment itself and for costs associated with load restrictions and strengthening measures. Five different assessment methods were selected to assess a set of 11 single-span bridges, ranging in span from 2·4 m to 15·2 m, with the objective of reviewing and rationalising current assessment guidelines for masonry arch bridges. The bridges chosen are a representative sample of the stone arch bridges on the Irish National Roads network. It was found that there is a significant variation in assessed capacity depending on the assessment method used. Limit state analysis methods were found to generally result in higher ratings for segmental bridges while elastic methods resulted in higher ratings for three-centred or semi-circular bridges. Assessment ratings found using the Military Engineering Experimental Establishment (MEXE) method were difficult to rationalise across the bridge set considered in this study. Following a review of the origins of the MEXE method and its current form as set out in the assessment guidance, it is recommended that its use as the predominant tool in a simplified assessment procedure is not appropriate and that a more rational approach is required for a more realistic and reliable calculation of bridge capacity. The development of an improved assessment methodology is being considered as part of the current study.
  • ItemOpen AccessAccepted version Peer-reviewed
    Progressive cracking of masonry arch bridges
    (Thomas Telford Ltd., 2016-06) Gibbons, N; Fanning, PJ; Gibbons, Niamh [0000-0001-5140-4441]
    Numerous methods are available for the assessment of masonry arch bridges at the ultimate limit state. However, there is a lack of suitable methods for assessing behaviour at service levels of loading. To address this, non-linear three-dimensional finite element (FE) models that consider constitutive material models enabling progressive cracking and failure of the complete structural system were used to investigate the development of damage for three masonry arch bridges at both service levels and at the ultimate capacity. All of the elements contributing to the strength of the structure were represented in the models, including the arch barrel, spandrel, abutments, fill and surrounding soil. This allowed for consideration of the longitudinal and transverse capacities, the stiffening effects of the spandrel walls, the restraint and load distribution provided by the fill, the frictional behaviour between the masonry and fill, movement at the abutments and multiple causes of failure. While complex non-linear FE models are able to identify the ultimate load capacity there are alternative simpler approaches available for this, and it is the investigation of damage and crack propagation at service level loads where their use is of greatest benefit.
  • ItemOpen AccessAccepted version Peer-reviewed
    Road Design Layer Detection in Point Cloud Data for Construction Progress Monitoring
    (American Society of Civil Engineers (ASCE), 2018) Vick, Steven; Brilakis, Ioannis; Vick, Steven [0000-0002-4902-480X]; Brilakis, Ioannis [0000-0003-1829-2083]
    Poor performance in transportation construction is well-documented, with an estimated $114.3 billion in global annual cost overrun. Studies aimed at identifying the causes highlighted traditional project management functions like progress monitoring as the most important contributing factors. Current methods for monitoring progress on road construction sites are not accurate, consistent, reliable, or timely enough to enable effective project control decisions. Automating this process can address these inefficiencies. The detection of layered design surfaces in digital as-built data is an essential step in this automation. A number of recent studies, mostly focused on structural building elements, aimed to accomplish similar detection but the methods proposed are either ill-suited for transportation projects or require labelled as-built data that can be costly and time consuming to produce. This paper proposes and experimentally validates a model-guided hierarchical space partitioning data structure for accomplishing this detection in discrete regions of 3D as-built data. The proposed solution achieved an F1 Score of 95.2% on real-world data confirming the suitability of this approach.
  • ItemOpen Access
    Deformation mechanisms of idealised cermets under multi-axial loading
    (Elsevier BV, 2017) Bele, E; Goel, A; Pickering, EG; Borstnar, G; Katsamenis, OL; Pierron, F; Danas, K; Deshpande, VS
    The response of idealised cermets comprising approximately 60% by volume steel spheres in a Sn/Pb solder matrix is investigated under a range of axisymmetric compressive stress states. Digital volume correlation (DVC) analysis of X-ray micro-computed tomography scans (μ-CT), and the measured macroscopic stress-strain curves of the specimens revealed two deformation mechanisms. At low triaxialities the deformation is granular in nature, with dilation occurring within shear bands. Under higher imposed hydrostatic pressures, the deformation mechanism transitions to a more homogeneous incompressible mode. However, DVC analyses revealed that under all triaxialities there are regions with local dilatory and compaction responses, with the magnitude of dilation and the number of zones wherein dilation occurs decreasing with increasing triaxiality. Two numerical models are presented in order to clarify these mechanisms: (i) a periodic unit cell model comprising nearly rigid spherical particles in a porous metal matrix and (ii) a discrete element model comprising a large random aggregate of spheres connected by non-linear normal and tangential “springs”. The periodic unit cell model captured the measured stress-strain response with reasonable accuracy but under-predicted the observed dilation at the lower triaxialities, because the kinematic constraints imposed by the skeleton of rigid particles were not accurately accounted for in this model. By contrast, the discrete element model captured the kinematics and predicted both the overall levels of dilation and the simultaneous presence of both local compaction and dilatory regions with the specimens. However, the levels of dilation in this model are dependent on the assumed contact law between the spheres. Moreover, since the matrix is not explicitly included in the analysis, this model cannot be used to predict the stress-strain responses. These analyses have revealed that the complete constitutive response of cermets depends both on the kinematic constraints imposed by the particle aggregate skeleton, and the constraints imposed by the metal matrix filling the interstitial spaces in that skeleton.
  • ItemOpen AccessPublished version Peer-reviewed
    Building response to tunnelling
    (Elsevier BV, 2014-06) Farrell, Ruaidhri; Mair, Robert; Sciotti, Alessandra; Pigorini, Andrea
  • ItemOpen AccessAccepted version Peer-reviewed
    Discussion of “A cantilever approach to estimate bending stiffness of buildings affected by tunnelling” by Twana Kamal Haji, Alec M. Marshall, and Walid Tizani
    (Elsevier BV, 2018) Franza, A; DeJong, MJ; Franza, Andrea [0000-0002-8510-0355]; De Jong, Matthew [0000-0002-6195-839X]
    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.
  • ItemOpen Access
    Experimental Study of the Influence of Bond on the Flexural Behaviour of Concrete Beams Pre-tensioned with AFRPs
    (The American Concrete Institute, 1999-06) Lees, Burgoyne CJ Janet M
    An experimental program was formulated to investigate the flexural behaviour of concrete prestressed with aramid fibre reinforced plastic tendons (AFRPs). The particular focus was the influence of the bond between an AFRP tendon and concrete on the flexural response of a beam. In the main test series pre-tensioned concrete beams were cast using either one of two types of AFRP tendons or steel tendons. The influence of bond was studied by testing beams with fully-bonded tendons, unbonded tendons or partially-bonded tendons. It was found that, although the fully-bonded beams had a high ultimate load capacity, only limited rotation occurred prior to failure. In contrast, large rotations were noted in the unbonded beams but the strengths of these members were significantly (25%) lower than those of the fully-bonded beams. The only beams that achieved both a high rotation capacity and a high ultimate load capacity were the beams with partially-bonded tendons. It is suggested that the use of partially-bonded tendons could provide the basis of a new design method for concrete beams prestressed with FRPs.
  • ItemOpen Access
    Expansive cement couplers - a means of pre-tensioning fibre reinforced plastic tendons
    (Elsevier BV, 1995) Lees, JM; Gruffyd Jones, B; Burgoyne, CJ; Lees, Janet [0000-0002-8295-8321]; Burgoyne, Christopher [0000-0002-8092-3344]
    Fibre reinforced plastics describes a group of materials composed of inorganic or organic fibres embedded in a resin matrix. frps are strong, non-magnetic, light-weight and for the most part, non-corrodable. There is great scope for the use of frps as concrete reinforcement and the high strength of the materials is conducive to prestressed applications. However, finding a suitable method of anchoring the tendons without inducing stress concentrations in the fibres has been identified as a problem. The current paper investigates the potential for the use of expansive cement couplers as a means of pretensioning frp tendons. An experimental study was carried out on couplers to join steel reinforcing bars and then extended to include the coupling of frp materials to steel prestress wire.
  • ItemOpen Access
    Analysis of concrete beams with partially bonded composite reinforcement
    (American Concrete Institute, 2000) Lees, JM; Burgoyne, CJ; Lees, Janet [0000-0002-8295-8321]; Burgoyne, Christopher [0000-0002-8092-3344]
    Beams prestressed with partially bonded fiber-reinforced plastic (FRP) tendons have high strength and rotation capacity but cannot be modeled by conventional techniques. Herein, it is assumed that all deformation takes place at cracks between rigid bodies. By setting up appropriate compatibility and equilibrium equations, the behavior at a single crack can be modeled, which then allows predictions to be made as to which of four possible events will occur next. These lead either to beam failure, or to changes in the geometry that can be analyzed using the same techniques. Comparisons are made with test results, and reasonable agreement is shown.
  • ItemOpen Access
    Fibre-reinforced polymers in reinforced and prestressed concrete applications: moving forward
    (Wiley, 2001) Lees, JM; Lees, Janet [0000-0002-8295-8321]
    AbstractRecent developments in the use of fibre‐reinforced polymers (FRPs) in reinforced and prestressed concrete applications are reviewed. The influence of FRP material properties on the design of concrete structures is considered and applications are discussed in conjunction with the structural function of the FRP reinforcement. The review includes examples of the practical implementation of the technology and addresses important durability issues. A number of future considerations/research needs are identified and the requirement for the provision of standard, sustainable and cost‐effective FRP solutions is highlighted. It is concluded that although there have been significant advances in our knowledge of the behaviour of FRP‐concrete structures, the timeframe in which FRPs will no longer be considered as new materials remains ambiguous.
  • ItemOpen Access
    Flexural fatigue performance of CFRP prestressed concrete poles
    (SAGE Publications, 2012) Roberts, EE; Lees, JM; Hoult, NA; Lees, Janet [0000-0002-8295-8321]
    Carbon fibre reinforced polymer (CFRP) prestressed concrete poles offer a durable, light-weight alternative to conventional steel-reinforced or prestressed concrete poles. In particular, the corrosion resistance of the CFRP tendons can result in lower maintenance costs and a reduction in the required concrete cover. For lighting poles used in pedestrian or low-trafficked areas, wind loading represents a dominant load case. The wind acts as a transient force and can blow from any direction. It is therefore of interest to investigate how CFRP prestressed lighting poles perform under repeated cyclic loads and/or load reversals. Experiments were carried out on pole sections tested horizontally. These included a static control test and a conventional fatigue test where a cyclic load was applied in a downwards direction for 2 million cycles. Three further fatigue tests where the load direction changed, either after a defined number of cycles or within a load cycle, were also conducted. It was found that all the poles performed adequately for 1–2 million cycles of loading and that the majority of any deflection increases occurred within the first 50,000 cycles. It is believed that repeated cyclic loading may have increased the tendon debonding at the crack locations. Localised debonding potentially relieves the stress in the outermost tendon layer which delays the onset of failure and allows the inner tendon layers to take up further stress thus leading to a higher load carrying capacity. Loading orientation reversal from a downwards to an upwards direction within a loading cycle did not result in a greater stiffness degradation when compared to the other fatigue tests. The initial findings suggest that in-service cyclic loading and load reversals will not be detrimental to the performance of CFRP prestressed concrete poles.
  • ItemOpen Access
    Precracked reinforced concrete t-beams repaired in shear with prestressed carbon fiber-reinforced polymer straps
    (American Concrete Institute, 2013) Dirar, S; Lees, JM; Morley, CT; Lees, Janet [0000-0002-8295-8321]
    The results of an experimental and numerical investigation involving unstrengthened reinforced concrete (RC) T-beams and precracked RC T-beams strengthened in shear with prestressed carbon fiber-reinforced polymer (CFRP) straps are presented and discussed. The results provide insights into the influence of load history and beam depth on the structural behavior of both unstrengthened and strengthened beams. The strengthened beams exhibited capacity enhancements of 21.6 to 46% compared to the equivalent unstrengthened beams, demonstrating the potential effectiveness of the prestressed CFRP strap system. Nonlinear finite element (FE) predictions, which incorporated the load history, reproduced the observed experimental behavior but either underestimated or overestimated the post-cracking stiffness of the beams and strap strain at higher load levels. These limitations were attributed to the concrete shear models used in the FE analyses.
  • ItemOpen Access
    Precracked RC T-beams Repaired in Shear with Externally Bonded CFRP Sheets
    (American Concrete Institute, 2012-03-01) Dirar, Samir; Lees, Janet M; Morley, Chris T; Lees, Janet [0000-0002-8295-8321]
    This study investigates the structural behavior of precracked reinforced concrete (RC) T-beams strengthened in shear with externally bonded carbon fiber-reinforced polymer (CFRP) sheets. It reports on seven tests on unstrengthened and strengthened RC T-beams, identifying the influence of load history, beam depth, and percentage of longitudinal steel reinforcement on the structural behavior. The experimental results indicate that the contributions of the external CFRP sheets to the shear force capacity can be significant and depend on most of the investigated variables. This study also investigates the accuracy of the prediction of the fiber-reinforced polymer (FRP) contribution in ACI 440.2R-08, UK Concrete Society TR55, and fib Bulletin 14 design guidelines for shear strengthening. A comparison of predicted values with experimental results indicates that the guidelines can overestimate the shear contribution of the externally bonded FRP system.
  • ItemOpen Access
    CFRP prestressed concrete lighting columns
    (American Concrete Institute, 2003) Terrasi, GP; Lees, JM; Rizkalla, SH; Nanni, A; Lees, Janet [0000-0002-8295-8321]
    Aspects of the design and installation of a novel carbon fibre reinforced polymer (CFRP) prestressed high strength concrete lighting column (Carbolith®) are presented. The tapered cylindrical columns have a nominal height of 8 m and contain an opening above the foundation to allow for the insertion of the lamp fuse box. The bending/torsion behaviour of a total of five full-scale prototype columns was tested in accordance with the relevant European standards (EN). In the experimental programme, the location of the fuse box opening relative to the loading direction was varied. All five poles fulfilled the EN serviceability and ultimate limit state requirements for lighting columns in pedestrian and/or low speed lightly trafficked areas. This successful outcome has lead to the first field application of the CFRP prestressed concrete lighting columns.
  • ItemOpen Access
    Uptake induced swelling and thermal expansion of CFRP tendons
    (Thomas Telfort, 2009) Scott, P; Lees, JM; Lees, Janet [0000-0002-8295-8321]
    Carbon-fibre-reinforced polymer (CFRP) tendons can be used as a corrosion-resistant alternative to steel for reinforcing or prestressing concrete in aggressive marine environments. The design lives of many civil marine structures often span decades and so the long-term durability of the internal reinforcement is important. One significant, yet overlooked, aspect of CFRP tendon durability is its susceptibility to swell on absorption of aqueous solutions including water and salt water. This paper reviews uptake-induced swelling in CFRP materials and draws comparisons with studies of swelling caused by thermal effects. The diffusion of aqueous solutions and their interaction with the polymer matrix are identified as the primary mechanisms responsible for the swelling. Experimental details are presented that correlate the uptake of water and salt water to swelling observed in CFRP tendons. The results are contrasted with both uptake- and thermal-driven behaviour cited in the literature. Lamé's equations are used to estimate the magnitude of the resulting stresses induced in the surrounding concrete. The practical significance of the findings is discussed, including the potential for cracking in the surrounding concrete cover and the implications for the tendon–concrete bond.
  • ItemOpen Access
    Water, salt water, and alkaline solution uptake in epoxy thin films
    (Wiley, 2013) Scott, P; Lees, JM; Lees, Janet [0000-0002-8295-8321]
    ABSTRACTAs a means of characterizing the diffusion parameters of fiber reinforced polymer (FRP) composites within a relatively short time frame, the potential use of short term tests on epoxy films to predict the long‐term behavior is investigated. Reference is made to the literature to assess the effectiveness of Fickian and anomalous diffusion models to describe solution uptake in epoxies. The influence of differing exposure conditions on the diffusion in epoxies, in particular the effect of solution type and temperature, are explored. Experimental results, where the solution uptake in desiccated (D) or undesiccated (U) thin films of a commercially available epoxy matrix subjected to water (W), salt water (SW), or alkali concrete pore solution (CPS) at either 20 or 60°C, are also presented. It was found that the type of solution did not significantly influence the diffusion behavior at 20°C and that the mass uptake profile was anomalous. Exposure to 60°C accelerated the initial diffusion behavior and appeared to raise the level of saturation. In spite of the accelerated approach, conclusive values of uptake at saturation remained elusive even at an exposure period of 5 years. This finding questions the viability of using short‐term thin film results to predict the long‐term mechanical performance of FRP materials. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1898–1908, 2013
  • ItemOpen Access
    Nonlaminated FRP Strap Elements for Reinforced Concrete, Timber, and Masonry Applications
    (American Society of Civil Engineers (ASCE), 2011-03) Lees, JM; Winistorfer, AU; Lees, Janet [0000-0002-8295-8321]
    Advances in material technology allow for the exploration of new structural forms and systems. In recent years, fiber-reinforced polymers (FRPs) have emerged as candidate materials for civil engineering applications, and the use of FRPs in construction has been an area of growing interest. Unidirectional high-strength FRPs are well-suited for use as tensioning elements, but anchorage details present a challenge. An alternative is to self-anchor the FRP tensioning element by winding thin layers of material around supports and then laminating all the layers together (a laminated strap) or by securing only the outermost layer to form a closed outer loop while the inner layers remain nonlaminated (a nonlaminated strap). Nonlaminated FRP straps have been found to have higher efficiencies than equivalent laminated straps, which is advantageous in high-tension applications. The suitability of nonlaminated FRP straps for use as unbonded tension elements provides scope for use in new construction and for the strengthening of existing structures. A review of nonlaminated carbon FRP strap system properties and applications in the context of reinforced concrete, timber, and masonry structures is presented.
  • ItemOpen Access
    External prestressed carbon fiber-reinforced polymer straps for shear enhancement of concrete
    (American Society of Civil Engineers (ASCE), 2002) Lees, JM; Winistoerfer, AU; Meier, U; Lees, Janet [0000-0002-8295-8321]
    The use of fiber-reinforced polymers (FRPs) for the strengthening and repair of existing concrete structures is a field with tremendous potential. The materials are very durable and, hence, ideally suited for use as external reinforcement. Although extensive work has been carried out investigating the use of FRPs for flexural strengthening, a fairly recent development is the use of these materials for the shear strength enhancement of concrete. The current system investigates the use of posttensioned, nonlaminated, carbon fiber-reinforced polymer (CFRP) straps as external shear reinforcement for concrete. Experiments were carried out on an unstrengthened control beam and beams strengthened with external CFRP straps. It was found that the ultimate load capacity of the strengthened beams was significantly higher than that of the control specimen. Existing design codes and analysis methods were found to underestimate the ultimate resistance of the control specimen and the strengthened beams. Nevertheless, the modified compression field theory provided insight into possible failure mechanisms and the influence of the strap prestress level on the structural behavior. It is concluded that the use of these novel stressed elements could represent a viable and durable means of strengthening existing concrete infrastructure.
  • ItemOpen Access
    Experimental behavior of reinforced concrete beams strengthened with prestressed CFRP shear straps
    (American Society of Civil Engineers (ASCE), 2007) Kesse, GK; Lees, JM; Lees, Janet [0000-0002-8295-8321]
    One promising means of increasing the capacity of existing shear-deficient beams is to strengthen the structure using external prestressed carbon fiber reinforced polymer (CFRP) straps. In this system, layers of CFRP tape are wrapped around a beam to form a strap that acts like a discrete unbonded vertical prestressing tendon. Experiments were undertaken to investigate the influence of the strap spacing, the strap stiffness, the initial strap prestress level and/or any preexisting damage on the strengthened behavior, and mode of failure. An unstrengthened control beam was tested and failed in shear. In contrast, all of the strengthened beams showed a significant increase in their ultimate load capacity with several of the strengthened beams failing in flexure. A number of different failure modes were noted and initial guidelines on the design parameters that influence the propensity for a particular failure mode were developed.