Showing papers in "Structure and Infrastructure Engineering in 2015"

Seismic fragility assessment of highway bridges: a state-of-the-art review

Abstract: Safety and serviceability of highway bridges, during and after an earthquake, is a prerequisite to ensure continuous transport facilities, emergency and evacuation routes. Recently, fragility curves have emerged as important decision support tools to identify the potential seismic risk and consequences during and after an earthquake. There has been a substantial increase in interest among researchers in the topic of seismic fragility assessment of highway bridges as evidenced by the growing number of published literature. Advanced computational techniques and available resources have led to the development of different methodologies for fragility assessment. This study presents a review of the different methodologies developed for seismic fragility assessment of highway bridges along with their features, limitations and applications. This study presents a review of available methodologies and identifies opportunities for future development. This study mainly focuses on the key features of different method...

Shear-flexural strength mechanical model for the design and assessment of reinforced concrete beams

Abstract: A conceptual model for the prediction of the shear-flexural strength of slender reinforced concrete beams with and without transverse reinforcement is presented. The model incorporates the shear transferred by the un-cracked concrete chord, along the crack's length, by the stirrups, if they are, and, in that case by the longitudinal reinforcement. After the development of the first branch of the critical shear crack, failure is considered to occur when the stresses at any point of the concrete compression chord reach the assumed biaxial stress failure envelope. A physical explanation is provided for the evolution of the shear transfer mechanisms, and the contribution of each one at ultimate limit state is formulated accordingly. Simple equations are derived for shear strength verification and for designing transverse reinforcement. The method is validated by comparing its predictions with the results of 1131 shear tests, obtaining very good results in terms of mean value and coefficient of variation. Beca...

A life cycle assessment of in-place recycling and conventional pavement construction and maintenance practices

Abstract: The application of in-place recycling techniques has emerged as a practical and effective way to enhance the sustainability of agency pavement management decisions for asphalt-surfaced pavements. However, the potential environmental benefits resulting from applying in-place recycling techniques have not been fully documented in the literature. This paper presents a comprehensive pavement life cycle assessment (LCA) model that extends the typical pavement LCA's system boundaries to include the environmental impacts resulting from the usage phase and the production of the energy sources. The results of the application of the pavement LCA model to a specific highway rehabilitation project in the state of Virginia showed that in-place recycling practices and an effective control of the pavement roughness can improve significantly the life cycle environmental performance of a pavement system.

Deteriorating beam finite element for nonlinear analysis of concrete structures under corrosion

Abstract: A three-dimensional reinforced concrete (RC) deteriorating beam finite element for nonlinear analysis of concrete structures under corrosion is presented in this study. The finite element formulation accounts for both material and geometrical nonlinearity. Damage modelling considers uniform and pitting corrosion and includes the reduction of cross-sectional area of corroded bars, the reduction of ductility of reinforcing steel and the deterioration of concrete strength due to splitting cracks, delamination and spalling of the concrete cover. The beam finite element is validated with reference to the results of experimental tests carried out on RC beams with corroded reinforcement. The application potentialities of the proposed formulation are shown through the finite element analysis of a statically indeterminate RC beam and a three-dimensional RC arch bridge under different damage scenarios and corrosion penetration levels. The results indicate that the design for durability of concrete structures expose...

Structural health monitoring of a cable-stayed bridge with Bayesian neural networks

Abstract: In recent years, there has been an increasing interest in permanent observation of the dynamic behaviour of bridges for long-term monitoring purpose. This is due not only to the ageing of a lot of structures, but also for dealing with the increasing complexity of new bridges. The long-term monitoring of bridges produces a huge quantity of data that need to be effectively processed. For this purpose, there has been a growing interest on the application of soft computing methods. In particular, this work deals with the applicability of Bayesian neural networks for the identification of damage of a cable-stayed bridge. The selected structure is a real bridge proposed as benchmark problem by the Asian-Pacific Network of Centers for Research in Smart Structure Technology (ANCRiSST). They shared data coming from the long-term monitoring of the bridge with the structural health monitoring community in order to assess the current progress on damage detection and identification methods with a full-scale example. T...

Optimisation model to schedule railway track renewal operations: a life-cycle cost approach

Abstract: Besides high initial construction costs, ballasted railway tracks also have high investment requirements, related to maintenance and renewal (M&R) works. Decision support tools for railway track components that optimise these works are increasingly gaining in importance. This paper presents an optimisation model that integrates ballast, rail and sleeper degradation models in a mixed integer linear programming model. This model links the decisions to renew these components with their condition and takes advantage of the integrated planning of renewal works to minimise the railway track life-cycle cost (LCC). The practical utility of the model is illustrated with a case study involving the Portuguese Lisbon–Porto line. The results indicate a reduction in track renewal cost if the grouping of components, track segments and time interval for renewal operations are optimised. Furthermore, this paper demonstrates that possible annual budget restrictions for railway track M&R operations can have an important inf...

Operational deformations in long-span bridges

Abstract: Long-span bridges deform quasi-statically and dynamically under a range of operational conditions including wind, traffic and thermal loads, in varying patterns, at different timescales and with different amplitudes. While external loads and internal forces can only rarely be measured, there are well-developed technologies for measuring deformations and their time and space derivatives. Performance data can be checked against design limits and used for validating conceptual and numerical models which can in turn be used to estimate the external loads and internal forces. Changes in performance patterns and load–response relationships can also be used directly as a diagnostic tool, but excessive deformations themselves are also a concern in terms of serviceability. This paper describes application of a range of measurement technologies, focusing on response to extreme loads, for suspension bridges over the River Tamar (with 335 m main span) and Humber (with 1410 m man span). The effects of vehicular, therm...

Bridge condition modelling and prediction using dynamic Bayesian belief networks

Abstract: The development of a condition-based deterioration modelling methodology at bridge group level using Bayesian belief network (BBN) is presented in this paper. BBN is an efficient tool to handle complex interdependencies within elements of engineering systems, by means of conditional probabilities specified on a fixed model structure. The advantages and limitations of the BBN for such applications are reviewed by analysing a sample group of masonry bridges on the UK railway infrastructure network. The proposed methodology is then extended to develop a time dependent deterioration model using a dynamic Bayesian network. The condition of elements within the selected sample of bridges and a set of conditional probabilities for static and time dependent variables, based on inspection experience, are used as input to the models to yield, in probabilistic terms, overall condition-based deterioration profiles for bridge groups. Sensitivity towards various input parameters, as well as underlying assumptions, on th...

Investment priorities for the management of hydraulic structures

Abstract: Maintenance management of the hydraulic structures requires the selection of the most necessary maintenance intervention to ensure their proper operation and structural safety. Given the characteristics of these structures, many types of damage may appear, so it is not easy to take a decision. The purpose of this paper is to present the Prioritisation Index for the Management of Hydraulic Structures (PIMHS), a multi-criteria decision-making system based on the three axioms of sustainability (social, environmental and economic), which orders and prioritises non-similar maintenance investments in hydraulic structures. The results obtained show that PIMHS can be used by decision-makers to prioritise, in hydraulic structures, all kinds of maintenance interventions where the damages cannot lead to dam break.

Under sleeper pads in transition zones at railway underpasses: numerical modelling and experimental validation

Abstract: In railway lines, transition zones between different track support conditions normally evidence higher degradation rates, thus requiring additional maintenance to ensure safety and service quality. Studies based on numerical simulations indicate that under sleeper pads (USP) can minimise those degradation rates. The study presented herein focuses on the influence of USP on the dynamic behaviour of transitions to underpasses, in an attempt to fill the gap between numerical and field studies. To that aim, the authors used finite element method models, calibrated and validated with field measurements. These models take into account the train–track interaction and include all relevant track components and backfill geomaterials. This study shows that soft USP have a significant influence over the track's dynamic behaviour: amplifying rail displacements and sleeper accelerations, and inducing abrupt variations in the track vertical stiffness and oscillations in train–track forces. To benefit from the use of USP...

Measuring and modelling the thermal performance of the Tamar Suspension Bridge using a wireless sensor network

Abstract: A study on the thermal performance of the Tamar Suspension Bridge deck in Plymouth, UK, is presented in this paper. Ambient air, suspension cable, deck and truss temperatures were acquired using a wired sensor system. Deck extension data were acquired using a two-hop wireless sensor network. Empirical models relating the deck extension to various combinations of temperatures were derived and compared. The most accurate model, which used all the four temperature variables, predicted the deck extension with an accuracy of 99.4%. Time delays ranging from 10 to 66 min were identified between the daily cycles of the air temperature and of the structural temperatures and deck extension. However, accounting for these delays in the temperature–extension models did not improve the models' prediction accuracy. The results of this study suggest that bridge design recommendations are based on overly simplistic assumptions which could result in significant errors in the estimated deck movement, especially for temperat...

Application of shape memory alloy bars in self-centring precast segmental columns as seismic resistance

Abstract: The objective of this study is to investigate analytically the performance of self-centring precast segmental bridge columns with shape memory alloy (SMA) starter bars under nonlinear static and lateral seismic loading. For this purpose, a 3D finite element model for hybrid post-tensioned bridge column has been developed. The precast post-tensioned segmental bridge columns possessing a central tendon and adequate transverse confinement provided by the steel tube jacketing as self-centring bridge columns have an undesirable high lateral seismic demand due to their low energy dissipation. In order to eliminate this deficiency while keeping the residual displacement small, SMA starter bars are applied in this system. The effect of post-tensioning (PT) forces of the central strands and SMA bar size are investigated. The results indicate that in high seismicity zones, bridge columns with SMA bars at a higher level of PT forces have a superior performance against earthquake loading.

Reinforced concrete and masonry arch bridges in seismic areas: typical deficiencies and retrofitting strategies

Abstract: In recent years, appraisal of the condition and rehabilitation of existing bridges has become an ongoing problem for bridge owners and administrators in all developed countries. Reliable methodologies are therefore needed in the assessment and retrofit design phases, to identify the vulnerability of each bridge class. The specific problems of common arch bridge types are discussed herein, for both reinforced concrete and masonry structures, proper interventions for their static and seismic retrofitting are illustrated and several examples of applications are provided. Retrofitting is usually coupled with functional refurbishment, according to a methodological approach that takes into account bridge characteristics, state of maintenance and functional requirements, and environmental aspects connected with repair and strengthening systems.

Probabilistic deterioration model of high-strength steel wires and its application to bridge cables

Abstract: Bridge inspections reveal that severe corrosion and fatigue are the main failure mechanisms of bridge stay cables. This paper presents an empirical modelling of the long-term deterioration process of steel wires in cables with consideration of the simultaneous occurrence of uniform corrosion, pitting corrosion and fatigue induced by a combined action of environmental aggression and cyclic loading. Accelerated corrosion experiments are conducted to determine the different corrosion levels of high-strength steel wires, and time-dependent statistical models are developed to quantify uniform and pitting corrosion depth. Corrosion-fatigue process of steel wires is subsequently simulated using the corrosion models and cyclic stress obtained through cable force monitoring data. The mechanical properties of corroded steel wires, including yield stress, ultimate stress, ultimate strain and modulus of elasticity, are experimentally characterised, and the statistical models are established through regression analysi...

Field-calibrated influence lines for improved axle weight identification with a bridge weigh-in-motion system

Abstract: Bridge weigh-in-motion (BWIM) systems take influence line (IL) as a reference to calculate axle weights. The calibrated ILs based on field measurements can acquire better conformity with the actual situation and more actually represent the characteristic of existing bridges. Following the methodology proposed by O'Brien et al. (2006), this paper presents back-calculating of the ILs from direct measurements taken on field tests for identification of axle weights of heavy vehicles. The algorithm for calibrating ILs is based on continuously measured bridge responses (strains) produced by two calibration vehicles passing across the instrumented bridge. In terms of the calibrated ILs, Moses' algorithm was applied to identify axle weights of moving vehicles by the least-square method. Field tests on highway US-78 in Alabama were conducted as a case study to evaluate the accuracy of the presented algorithms in calibrating ILs and to identify the axle weights by comparing with the static measurements, and with th...

On the use of under sleeper pads in transition zones at railway underpasses: experimental field testing

Abstract: The railway track at transition zones to bridges or to other structures usually requires considerably more interventions to maintain the same open track service quality and safety levels. Under sleeper pads (USP) have been reported to contribute to reduce degradation and frequency of maintenance operations in open ballasted tracks, and recent numerical studies have suggested its use in transition zones. In this study, the influence of using USP at transition zones to underpasses was investigated. The structural behaviour of two transitions to similar box culverts was compared. USP were added to the sleepers in one of the transitions. Track characterisation using non-destructive tests is presented and analysed. Measurements of track response from passing trains are also presented and discussed. Results indicate that USP influence the dynamic behaviour of the track, increasing its vertical flexibility and amplifying both rail displacements and sleeper accelerations.

Baseline-free real-time assessment of structural changes

Abstract: This article addresses the subject of data-driven structural health monitoring and proposes a real-time strategy to conduct structural assessment without the need to define a baseline period, in which the monitored structure is assumed healthy and unchanged. Independence from baseline references is achieved using unsupervised discrimination machine-learning methods, widely known as clustering algorithms, which are able to find groups in data relying only on their intrinsic features and without requiring prior knowledge as input. Real-time capability is based on the definition of symbolic data, which allows describing large amounts of information without loss of generality or structural-related information. The efficiency of the proposed methodology is illustrated using an experimental case study in which structural changes were imposed to a suspended bridge during an extensive rehabilitation programme. A single-value novelty index capable of describing multi-sensor data is proposed, and its effectiveness ...

A condition assessment model for oil and gas pipelines using integrated simulation and analytic network process

Abstract: Even though they are safe and economical transportation means of gas and oil products around the world, pipelines can be subject to failure and degradation generating hazardous consequences and irreparable environmental damages Therefore, gas and oil pipelines need to be effectively monitored and assessed for optimal and safe operation Many models have been developed in the last decade to predict pipeline failures and conditions However, most of these models used corrosion features as the sole factor to assess the condition of pipelines Therefore, the objective of this paper was to develop a condition assessment model of oil and gas pipelines that considers several factors besides corrosion The proposed model, which uses both analytic network process and Monte Carlo simulation, considers the uncertainty of the factors affecting pipeline condition and the interdependency relationships between them The performance of the model was tested on an existing offshore gas pipeline in Qatar and was found to b

Enhancement of flexural behaviour of CFRP-strengthened reinforced concrete beams using engineered cementitious composites transition layer

Abstract: This paper aimed to develop and evaluate an efficient strengthening method for reinforced concrete beams, based on engineered cementitious composites (ECC) to be applied as a transition layer prior to the application of the carbon fibre-reinforced polymer (CFRP) strengthening sheet. The role of the proposed transition layer is to control the cracking of concrete and detain or even avoid premature de-bonding of the strengthening CFRP sheets. As the ability of the transition layer to exhibit a strain hardening behaviour is mainly dependent on the used fibre volumetric ratio, three ECC mixes with three different polypropylene fibre volumetric ratios were used (fibre volumetric ratio of 0.5%, 1% and 1.5%). The experimental results showed that while the used CFRP strengthening sheet can increase the ultimate load by about 28.8% compared with the control un-strengthened beam, this increase can reach about 48.5% by applying the same CFRP sheet to the proposed ECC transition layer that contains a fibre volumetric...

Uplift of elastomeric bearings in isolated bridges subjected to longitudinal seismic excitations

Abstract: © 2014 Taylor & Francis Bearings are used to isolate bridge substructures from the lateral forces induced by creep, shrinkage and seismic displacements. They are set in one or two support lines parallel to the transverse axis of the pier cap and are typically anchored to the deck and to the pier cap. This detailing makes them susceptible to possible tensile loading. During an earthquake, the longitudinal displacements of the deck induce rotations to the pier caps about a transverse axis, which in turn cause tensile (uplift) and compressive displacements to the bearings. Tensile displacements of bearings, due to the pier rotations, have not been addressed before and questions about the severity of this uplift effect arise, because tensile loading of bearings is strongly related to elastomer cavitation and ruptures. An extended parametric study revealed that bearing uplift may occur in isolated bridges, while uplift effect is more critical for the bearings on shorter piers. Tensile displacements of bearings were found to be significantly increased when the isolators were eccentrically placed with respect to the axis of the pier and when flexible isolators were used for the isolation of the bridge. The results of this study cannot be generalised as bridge response is strongly case-dependent and the approach has limitations, which are related to the modelling approach and to the fact that emphasis was placed on the longitudinal response of bridges.

Capital renewal optimisation for large-scale infrastructure networks: genetic algorithms versus advanced mathematical tools

Abstract: Civil infrastructure assets require continuous renewal (repair, rehabilitation or replacement) actions to modernise the inventory and sustain its operability. Allocating limited renewal funds among numerous asset components, however, represents a complex optimisation problem. Earlier efforts using genetic algorithms (GAs) could optimise small size problems yet exhibiting steep degradation in solution quality as problem size increases. Even by applying sophisticated mechanisms such as ‘segmentation’ to improve the performance of GAs, large processing time hinders the practicality of the algorithm for large-scale problems. This article, therefore, aims at improving both processing speed and solution quality for very large-scale problems (up to 50,000 assets). The article develops optimisation models using an advanced modelling tool (GAMS/CPLEX), and compares its results with GAs on three different model formulations. Both approaches proved to be beneficial, yet the advanced mathematical approach showed supe...

Structural damage detection and localisation using multivariate regression models and two-sample control statistics

Abstract: This paper presents model-free damage identification and localisation methods based on two-sample control statistics as well as damage-sensitive features to be extracted from single- and multivariate regression models. For this purpose, sequential normalised likelihood ratio test and two-sample t-test are adopted to detect the change in two families of damage features based on the coefficients of four different linear regression models. The performance of combinations of these damage features, regression models and control statistics are compared through a scaled two-bay steel frame instrumented with a dense sensor network and excited by impact loading. It is shown that the presented methodologies are successful in detecting the timing and location of the structural damage, while having acceptable false detection quality. In addition, it is observed that incorporating multiple mathematical models, damage-sensitive features and change detection tests improve the overall performance of these model-free vibr...

Seismic performance of irregular bridges – comparison of different nonlinear static procedures

Abstract: The adequate seismic performance of transportation infrastructures is important for the functioning of the economy and society. This paper focuses on the seismic assessment and analysis of one of the most important components of these infrastructures, the bridges. In this field, nonlinear static procedures (NSPs) have gained significant attention, resulting in different proposals to improve the accuracy of the procedures while keeping their simplicity. The main goal of this study is focused on the evaluation of the applicability of NSPs for irregular reinforced concrete viaducts. A comparative approach is pursued by resorting to (1) the analyses of the performance of three well-known NSPs (N2 method, modal pushover analysis and adaptive capacity spectrum method) and (2) the extension of the scope of previous studies in this field to a more recent method, the extended N2. As such, a set of bridges with different levels of irregularity, configurations and lengths is investigated. The accuracy of different N...

Multi-impact source localisation on aircraft composite structure using uniform linear PZT sensors array

Abstract: Composite structures are often struck by foreign objects at multiple locations. Multiple dents may be found on the composite structures such that it is hard to determine the number of impact events. This research presents a multiple impacts localisation method based on the near-field 2D multiple signal classification (2D-MUSIC) method for the composite structure. When multiple impacts are loaded on the plate, it is difficult to localise the positions of multiple impacts because of the overlapping of elastic waves produced by multi-impacts and the edge reflection of the plate. The MUSIC approach can provide estimation of the parameters of multiple emitters without any signal separation of mixed multi-impacts. It is well known that the performance of the MUSIC algorithm largely depends on the successful determination of the number of impacts. Gerschgorin disc theorem is applied for estimating the number of impacts. To verify the proposed method, experiments were preformed on the composite structure. The est...

A multi-criteria analysis for bridge sustainability assessment: a case study of Penang Second Bridge, Malaysia

Abstract: Bridges are a critical part of our nation's economic prosperity and local community well-being. One of the latest trends in bridge engineering is sustainable design, which is designing so that resources are available for many generations to come. Sustainable design considers the ecological, economic and socio-cultural environments and works to balance all three. There are some sustainable infrastructure rating systems (RSs) available, such as Envision that can be applied to bridges. However, no system has been developed that would specifically apply to bridge sustainability assessment. The objectives of this study are first, to investigate bridge sustainability issues from three main aspects: environmental, economical and social; and second, to apply multi-criteria analysis to assess the sustainability of the Penang Second Bridge in Malaysia. A hierarchy structure of the sustainable bridge attributes was developed for each RS, and an analytical hierarchy process method was then applied for the appraisal o...

Kriging response surface reliability analysis of a ship-stiffened plate with initial imperfections

Abstract: The use of structural reliability methods with implicit limit state functions (LSFs) shows the increasing demand for efficient stochastic analysis tools, because the structural behaviour predictions are often obtained by finite element analysis. All stochastic mechanics problems can be solved by Monte Carlo simulation method, nevertheless, in most cases, at a prohibitively high computational cost. Several approximations can be achieved using first-order reliability method (FORM) and second-order reliability method and response surface methods. In this paper, a method that combines the FORM and Kriging interpolation models, as response surface, is proposed. The prediction accuracy of the Kriging response surface obtained from different sampling techniques is assessed, and the failure probability estimates calculated by the FORM using the classical second-order polynomial regression models and the Kriging interpolation models as surrogates of nonlinear LSFs are compared. The usefulness and efficiency of the...

Improving the structural robustness of multi-story steel-frame buildings

Abstract: Although there are numerous hazards that could trigger the progressive collapse of a building, there are limited provisions in related codes regarding the design of structures to withstand exposure to such threats. It is thus expedient to limit the extent of damage to prevent the initiation of progressive collapse. This could be done by usage of the alternate path method, whereby the structure is made to withstand the loss of one or more critical load-bearing elements and prevent disproportionate collapse. In our study, we investigated the resistance of seismically designed steel-frame buildings to progressive collapse, focusing on the contributions of the floor system and beam-to-column connections. The applied element method was used to predict the structural response by nonlinear static and dynamic analyses, with the purpose of determining some robustness criteria, using as reference the ratio of the failure load to the nominal gravity load.

Life cycle cost optimisation in highway concrete bridges management

Abstract: This study presents a life cycle cost prediction and cost minimisation methodology for a set of highway concrete bridges, during a medium or a long period of time, in order to facilitate the decision process of the structure management. This methodology takes into consideration bridge intervention costs in addition with some Markov matrices degradation model. It applies a genetic algorithm in order to identify the optimised intervention plan, considering the available budget and the desired minimum performance level. Some Portuguese direct and indirect cost parameters, associated with different types of interventions during bridges lifetime, are presented. Finally, a probabilistic sensitivity analysis is carried out using Monte Carlo simulations.

The influence of infilled panels in retrofitting interventions of existing reinforced concrete buildings: a case study

Abstract: During the seismic events occurred in the last decades, the existing reinforced concrete (RC) building stock has often exhibited a significant brittle collapse of joints and secondary elements such as infill walls. A quite common strategy, in the attempt of mitigating this vulnerability, is the generalised implementation of strengthening interventions on the structural elements, even in the absence of a complete seismic assessment procedure. This paper presents some considerations about the effects induced by strengthening interventions involving the tying of the infill panels to the RC frame. Within this context, an appraisal of the actual displacement capacity and the possible alteration induced on the global collapse mechanism is provided. The analyses and discussion of results are presented with reference to an actual case study concerning a school building, which was part of a wide vulnerability assessment investigation performed in the Province of Foggia, Italy. In particular, seismic analyses perfo...

Experimental monitoring of chloride-induced reinforcement corrosion and chloride contamination in concrete with ground-penetrating radar

Abstract: In this article, we present a laboratory experiment to monitor the accelerated corrosion in concrete using ground-penetrating radar (GPR). Four concrete test specimens were cast with rebars of different size and placed at different depths. The lifetime decades of reinforcement corrosion process were accelerated into 18 days by using the impress current technique. The electrochemical corrosion process was periodically monitored with GPR. Two control specimens were also prepared to investigate the influence of chloride contamination on GPR signal. The measured data were analysed both in time and frequency domains. In time domain, the peak-to-peak amplitude of a wave reflected by a rebar was calculated to investigate the relationship between an increase in signal amplitude and the degree of corrosion. In frequency domain, the time–frequency representations of the signal were computed by using S-transform. The results show that reinforce corrosion increased the amplitude of reflected signal in time domain but...