Showing papers in "Structure and Infrastructure Engineering in 2013"

The consistency of visual sewer inspection data

Abstract: In common with most infrastructure systems, sewers are often inspected visually. Currently, the results from these inspections inform decisions for significant investments regarding sewer rehabilitation or replacement. In practice, the quality of the data and its analysis are not questioned although psychological research indicates that, as a consequence of the use of subjective analysis of the collected images, errors are inevitable. This article assesses the quality of the analysis of visual sewer inspection data by analysing data reproducibility; three types of capabilities to subjectively assess data are distinguished: the recognition of defects, the description of defects according to a prescribed coding system and the interpretation of sewer inspection reports. The introduced uncertainty is studied using three types of data: inspector examination results of sewer inspection courses, data gathered in day-to-day practice, and the results of repetitive interpretation of the inspection results. After a thorough analysis of the data it can be concluded that for all cases visual sewer inspection data proved poorly reproducible. For the recognition of defects, it was found that the probability of a false positive is in the order of a few percent, the probability of a false negative is in the order of 25%.

Monte Carlo simulation of extreme traffic loading on short and medium span bridges

Abstract: The accurate estimation of site-specific lifetime extreme traffic load effects is an important element in the cost-effective assessment of bridges. A common approach is to use statistical distributions derived from weigh-in-motion measurements as the basis for Monte Carlo simulation of traffic loading. However, results are highly sensitive to the assumptions made, not just with regard to vehicle weights but also to axle configurations and gaps between vehicles. This paper presents a comprehensive model for Monte Carlo simulation of bridge loading for free-flowing traffic and shows how the model matches results from measurements on five European highways. The model has been optimised to allow the simulation of many years of traffic and this greatly reduces the variance in calculating estimates for lifetime loading from the model. The approach described here does not remove the uncertainty inherent in estimating lifetime maximum loading from data collected over relatively short time periods.

Automated image processing technique for detecting and analysing concrete surface cracks

Abstract: In the present work, an image processing technique that automatically detects and analyses cracks in the digital image of concrete surfaces is proposed. The image processing technique automates the measurement of crack characteristics including the width, length, orientation and crack pattern. In the proposed technique, a morphological technique was applied to correct the non-uniform brightness of the background, and enhanced binarisation and shape analysis were used to improve the detection performance; furthermore, detailed algorithms to calculate the crack width, length, orientation and an artificial neural network to recognise crack patterns including horizontal, vertical, diagonal (−45°), diagonal (+45°), and random cracks are proposed. An image processing program was developed for the proposed algorithm and a series of experimental and analytical investigations were performed to assess the validity of the algorithm. Then, the crack characteristics measured using the proposed technique were compared ...

Modelling the structural behaviour of frost-damaged reinforced concrete structures

Abstract: A methodology is introduced to predict the mechanical behavior of reinforced concrete ‎structures with an observed amount of frost damage at a given time. It is proposed that the ‎effects of internal frost damage and surface scaling can be modeled as changes of material ‎and bond properties, and geometry, respectively. These effects ‎were studied and suggestions were made to relate the compressive strength and dynamic modulus of elasticity, as the indicators of damage, to the response of the damaged concrete in compression and tension, and to the bond behavior. The ‎methodology was applied to concrete beams affected by internal frost damage, using ‎non-linear finite element analyses. A comparison of the results ‎with available experimental data indicated that the changes in failure mode and, to a rather large extent, the effect on failure load ‎caused by internal frost damage can be predicted. However, an uncertainty was the extension and distribution of the damaged region which affected the prediction of the load capacity.‎

Bridge retrofit prioritisation for ageing transportation networks subject to seismic hazards

Abstract: The deteriorating state of highway bridges is traditionally ignored in estimating the seismic reliability of transportation networks. In this study, the present day seismic reliability of ageing bridges in highway networks is evaluated through a time-dependent seismic fragility analysis of typical bridge classes. An efficient algorithm based on finite-state Markov Chain Monte Carlo simulations is also presented to assess the reliability of large ageing highway bridge networks without the need to simplify the network topology. The criticality of ageing bridges is then assessed through different proposed ranking strategies to arrive at an optimised seismic retrofit prioritisation. A case study on an existing bridge network with 515 bridges in the state of South Carolina, USA reveals striking differences between results of the proposed ranking strategies and those from state-of-the-practice methods. Such differences emphasise the significance of accounting for network-level importance in seismic retrofit pro...

Seismic risk assessment of reinforced concrete bridges in flood-prone regions

Abstract: This article presents a conditional seismic risk evaluation framework of bridges located in seismically active flood-prone regions. Flood-induced bridge scour causes loss of lateral support at bridge foundations and thus the effect of seismic hazard on bridge performance gets amplified. Two example reinforced concrete bridges located in Sacramento County in California are considered. The regional multihazard scenario is characterised by combining scour resulted from regional flood events of different intensities with a suite of earthquake ground motions that represents regional seismicity. Uncertainties in the hazard models are discussed and their influences on bridge performance are investigated. A separate set of analysis is performed to evaluate the bridge performance only under earthquake ground motions. Seismic fragility curves and risk curves for the example bridges are generated. Result shows higher seismic risk of bridges when the impact of regional flood hazard on bridges is considered in the ana...

Decentralised green infrastructure: the importance of stakeholder behaviour in determining spatial and temporal outcomes

Abstract: The traditional approaches to resolving urban stormwater problems include costly expansion of collections systems and/or creation of in-line storage and treatment capacity. An emerging ‘green’ infrastructure (GI) approach would instead reduce runoff sources. An agent-based model is used to explore the spatiotemporal emergence of rain gardens and green roofs in Point Breeze, a 175 ha neighbourhood in South Philadelphia, PA, under two different scenarios. In the first, household GI adoption rules consider only economic self-interest and the physical compatibility of each GI technology with lot characteristics. In the second scenario, the adoption rules are enhanced based on insights into the possible behaviour of property owners, as intuited by the designers/authors over a two-year period using a variety of empirical methods. In Scenario 2, relevant knowledge and perceptions are transferred to household decision-makers through social networks, and exposure to GI is assumed to diffuse GI innovation. The two ...

Algorithms for bottom-up maintenance optimisation for heterogeneous infrastructure systems

Abstract: This paper presents a methodology for maintenance optimisation for heterogeneous infrastructure systems, i.e., systems composed of multiple facilities with different characteristics such as environments, materials, and deterioration processes. We present a bottom-up approach: facility-level optimal maintenance policies are first found; these policies are then combined with budget constraints in the system-level optimisation. In the first step, optimal and near-optimal maintenance policies for each facility are found and used as inputs for the system-level optimisation. In the second step, the problem is formulated as a constrained combinatorial optimisation problem, where the best combination of facility-level optimal and near-optimal solutions is identified. Two heuristics, pattern search heuristic (PSH) and evolutionary algorithm (EA), are adopted to solve the combinatorial optimisation problem. Their performance is evaluated using a hypothetical system of pavement sections. Comparison result with real ...

Fatigue reliability analysis of steel bridge details based on field-monitored data and linear elastic fracture mechanics

Abstract: This article presents the fatigue reliability analysis of welded details of a 40-year old steel box-girder bridge, based on the linear elastic fracture mechanics (LEFM) and the long-term stress monitoring. The fatigue crack growth is described by using the LEFM, based on which the ultimate limit state is established as a function of the crack size. Effective stress ranges are obtained from daily stress range histograms, and lognormal probability density functions (PDFs) are used to model the uncertainties in stress data. Details at discontinuous backing bar splices, which have not been explicitly listed in the American Association of State Highway and Transportation Officials (AASHTO) specification, and the welded details at the base of bridge bents are evaluated on their fatigue reliabilities. It is found that the backing bar splice detail may have high fatigue reliability, considering that low stress ranges and small number of cycles occurred in the monitoring period. For the weld detail at the base of ...

Reviewing the past to learn in the future: making sense of design errors and failures in construction

Abstract: Design errors can severely jeopardise safety and contribute to failures in construction and engineering projects. Such failures can have devastating economic, environmental and social consequences....

Hierarchical infrastructure network representation methods for risk-based decision-making

Abstract: Estimating the extent of hazard-induced damage to infrastructure networks is a complex task that goes beyond computing direct costs and requires considering the effect of network connection patterns and interactions. This article presents a new model that combines a systems approach with strategies for detecting the internal structure of networks, and providing flexibility and different levels of accuracy in estimating the extent of damage. The model describes networks as hierarchical structures obtained by successive clustering. Hierarchical analysis of networks provides unique insights about how damage affects performance throughout the whole infrastructure system. The model enables using information for decision-making more efficiently by generating different levels of resolution for different problems. This is illustrated using data from hurricane Ike, Texas, USA in 2008, where the primary transportation network is studied. Estimates of population affected and loss of productivity are discussed, empha...

Determining the probability distribution of rework costs in construction and engineering projects

Abstract: Rework arises due to design errors, changes and omissions during design and has been found to contribute to 52% of a project's cost overrun. The statistical characteristics of rework costs experienced from contract award in 276 construction and engineering projects were analysed. The skewness and kurtosis values of rework costs are computed to determine if the empirical distribution of the data follows a normal distribution. The empirical distributions for rework costs are found to be non-Gaussian. Theoretical probability distributions are fitted to the rework data. The Kolmogorov–Smirnov and Anderson–Darling non-parametric tests are used to determine the ‘Goodness of Fit’ of the selected probability distributions. A Generalised Pareto probability function is found to provide the best overall distribution fit for rework costs. The Generalised Pareto distribution is used to calculate the probability of rework being experienced for the selected sample. Projects with a contract value

Life cycle assessment of a railway bridge: comparison of two superstructure designs

Abstract: Railway bridges currently encounter the challenges of increasing the load capacity while the environmental sustainability should be achieved. However, it has been realized that the environmental assessment of railway bridges has not been integrated into the decision making process, the standard guideline and criterion is still missing in this field. Therefore, the implementation of life cycle assessment (LCA) method is introduced into railway bridges. This paper provides a systematic bridge LCA model as a guideline to quantify the environmental burdens for the railway bridge structures. A comparison case study between two alternative designs of Banafjal Bridge is further carried out through the whole life cycle, with the consideration of several key maintenance and EOL scenarios. Six impact categories are investigated by using the LCA CML 2001 method and the known LCI database. Results show that the fixed-slab bridge option has a better environmental performance than the ballasted design due to the ease of maintenances. The initial material manufacture stage is responsible for the largest environmental burden, while the impacts from the construction machinery and material transportations are ignorable. Sensitivity analysis illustrates the maintenance scenario planning and steel recycling have the significant influence on the final results other than the traffic disturbances.

Finite element model updating on small-scale bridge model using the hybrid genetic algorithm

Abstract: Finite element (FE) model-based dynamic analysis has been widely used to predict the dynamic characteristics of civil structures. FE model updating method based on the hybrid genetic algorithm, by combining genetic algorithm and the modified Nelder–Mead's simplex method, is presented to improve bridge structures' FE model. An objective function is formulated as a linear combination of fitness functions on natural frequencies, mode shapes and static deflections using measurements and analytical results to update both stiffness and mass simultaneously. A commercial FE analysis tool, which can utilise previously developed element library and solution algorithms, is adopted for applications on diversified and complex structures. The validity of the proposed method is verified by using a simply supported bridge model with three I-shaped girders. FE models such as grid, beam-shell and shell model are considered to modify initial FE models on the experimental structure. Experimental results suggest that the prop...

Multiobjective optimisation algorithm for sewer network rehabilitation

Abstract: Understanding of deterioration mechanisms in sewers helps asset managers in developing prediction models for estimating whether or not sewer collapse is likely. Effective utilisation of deterioration prediction models along with the development and use of life cycle maintenance cost analysis contribute to reducing operation and maintenance costs in sewer systems. This article presents a model for life-cycle maintenance planning of deteriorating sewer network as a multi-objective optimisation problem that treats the sewer network condition and service life as well as life-cycle maintenance cost (LCMC) as separate objective functions. The developed model utilises Markov chain model for the prediction of the deterioration of the network. A multi-objective genetic algorithm is used to automatically locate an appropriate maintenance scenario that exhibits an optimised tradeoff among conflicting objectives. Monte Carlo simulation is used to account for LCMC uncertainties. The optimisation algorithm provides an ...

Condition assessment for bridges: a hierarchical evidential reasoning (HER) framework

Abstract: Infrastructure risk management practices enable decision-makers to effectively monitor and assess structural condition for repairing/replacing elements before major damage or collapse state is reached Improved techniques have enhanced inspection and monitoring of infrastructure, but assessment and interpretation of the collected data remains a challenge In this article, a hierarchical evidential reasoning (HER) framework is proposed for the condition assessment of bridges The approach involves using a HER framework for classifying bridge data into primary, secondary, tertiary and life safety-critical elements The proposed HER framework combines different distress indicators (bodies of evidence) at different hierarchical levels The information is aggregated using Dempster–Shafer (D–S) and Yager rule of combination to propagate both aleatory and epistemic uncertainties throughout the model Furthermore, importance and reliability factors (collectively termed ‘‘credibility factor’) are introduced for di

Inspection, condition evaluation and replacement of elastomeric bearings in road bridges

Abstract: This paper presents the results of an inspection campaign as well as condition evaluation and replacement of more than 1000 elastomeric bridge bearings under service on the Isfahan state highway bridges constructed before 1990. It is the first comprehensive survey of this kind. The research was accomplished through inspection surveys, analysis of existing bridge maintenance data, condition evaluation and replacement of a significant portion of the inspected bearings and expert interviews. Inspection surveys and analysis of extracted data identified the problems and their causes and the merits and potential improvement of performance of each one of the inspected elastomeric bearings. Replacement of the damaged bearings with new ones was performed based on the results of this stage. The expert interviews investigated the practices of Isfahan and surrounding states regarding the selection of bearing manufacturers, the performance and the quality control of elastomeric bearings.

Safety requirements and probabilistic models of resistance in the assessment of existing railway bridges

Abstract: This article presents a summary description of the main safety criteria and requirements adopted in the ‘Guideline for Load and Resistance Assessment of Existing European Railway Bridges – advices on the use of advanced methods’ (SB-LRA, 2007. Prepared by Sustainable Bridges – a project within EU FP6. Available from: www.sustainablebridges.net) developed within the European project Sustainable Bridges – Assessment for Future Traffic Demands and Longer Lives. It shows selected safety formats recommended for the assessment of existing bridges, starting from the most simple, for the member level assessment, and ending with the most advanced, for the probabilistic non-linear assessment of a bridge system. The article also presents simplified methods for the probabilistic non-linear assessment of bridge systems. Furthermore, it shows probabilistic models for the resistance of selected types of bridge main carrying members that may be used in the simplified probabilistic assessment of existing railway bridges.

A holistic approach to asset management in the Netherlands

Abstract: The objective of the national agency for road and water infrastructure in the Netherlands is to deliver best service to the public at lowest life cycle cost, given public acceptable risk. This requires a sound and well-structured system of management and maintenance. Such a system consists of elements such as reliable asset data, long-term performance based maintenance programmes, clear steering objectives and transparent procurement strategies. Asset management will make it possible to show what network performance can be achieved, at which costs and with which associated risks. A model defining an asset owner role, an asset manager role and a service provider role was chosen as a governing principle for the design of the asset management process. The design of the process described in the paper sets the boundary conditions to carry out projects with the minimum amount of hindrance for the user while involving the market in the best possible way.

Procedure for determining the seismic vulnerability of an irregular isolated bridge

Abstract: A seismic vulnerability procedure, based on the capacity/demand ratio approach, is applied to an irregular isolated bridge. Special features are incorporated in both, demand estimation and capacity evaluation. The seismic demand is represented by an average pseudo-acceleration spectrum derived from 159 earthquake accelerograms recorded in the region where the bridge is located. The capacity spectrum method is adopted for estimating the structural expected performance for several limit states. The capacity curve derived from a static non-linear procedure is obtained by means of a lateral load pattern that follows the displacement configuration, previously assessed by the use of time history analyses of the bridge supported on non-linear isolator bearings. Based on a moment–curvature analysis of the pier's sections, the maximum curvature ductility was established for each of the four defined performance limit states. Finally, probability density functions of the bridge capacity and demand were assessed and ...

Three-dimensional modelling of structural effects of corroding steel reinforcement in concrete

Abstract: The effect of corrosion products flowing through cracks becomes significant when large corrosion penetrations take place in reinforced concrete structures and wide cracks develop; this is favorable, as it decreases the splitting stress around the bar. The effect becomes more important when the corrosion rate is low, such as for natural corrosion. A corrosion model describing the expansion due to voluminous corrosive products was previously developed. The model is here extended to include the flow of corrosion products through cracks. The volume flow of corrosion products through a crack is assumed to depend on the splitting stress and the crack width. The splitting stress is evaluated from the strain in the corrosion products, and the crack width is computed from the displacements across the crack. A one-dimensional flow model is used to formulate the flow phenomenon and to estimate the volume flow of corrosion products. The extended corrosion model, applied in detailed three-dimensional non-linear finite element analyses of highly corroded eccentric pull-out specimens, resulted in more corrosion cracks with smaller crack openings, which better corresponded to measurements of the tested specimens. Moreover, the results indicated the important effect of the flow phenomenon on the bond strength.

Damages of the Shaohuoping road tunnel near the epicentre

Abstract: Numerous infrastructures including national roads, tunnels, etc. in Sichuan Province were damaged to various extents in China's Wenchuan earthquake in 2008. The Shaohuoping road tunnel, near the epicentre of the earthquake, was the typical damaged one. The damage modes of different parts of the Shaohuoping tunnel were summarised based on the spot investigation data. It was found that various damages involving cracking and spalling of concrete lining were observed on different parts of the tunnel. The earthquake damages of critical positions, portal section and body portion, were simulated and analysed by finite element numerical model proposed in this paper. Influences of vertical motion on seismic responses of the tunnel were also studied by means of the finite element simulation. The simulation responses were compared with the spot investigations of earthquake structural damages to different parts of the tunnel. The comparisons showed a good agreement, which indicated that, the damage mechanism of the t...

Simulation-based life cycle cost modeling and maintenance plan for water mains

Abstract: Life cycle cost (LCC) is an essential approach to decide on alternative rehabilitation strategies for infrastructure systems, such as water mains. The research presented in this article identifies several rehabilitation methods for water mains, which are classified into three main categories: repair, renovation and replacement. A simulation-based LCC (SLCC) model is developed to compare different rehabilitation scenarios/alternatives for various types of water mains (i.e. cast iron, ductile iron, concrete, polyvinyl chloride and asbestos cement). Results show that ‘open trench’ and ‘slip lining’ are the most appropriate methods for the ‘repair’ and ‘renovation’ categories, respectively. However, the most suitable method for the ‘replacement’ category is ‘pipe bursting’ for pipe diameters less than 750 mm ( 30″). A rehabilitation plan is developed based on the SLCC results. This plan recommends repairing pipes using ‘open trench’ until the breaka...

Life-cycle social analysis of motorway bridges

Abstract: User costs of a bridge are the costs incurred by the users of the bridge, which result from any construction and/or maintenance activity being performed in the bridge. Typically, these costs encompass the additional time lost due to incurred congestion, the additional costs of vehicle operation and the costs of additional accidents. Usually, such costs are not considered in the procedures leading to the formulation of strategies for bridge construction, maintenance and repair, despite their relevance in comparison with the costs incurred by the agency or owner of the bridge. Moreover, in a life-cycle perspective of a bridge, with a time span over 100 years, the quantification of user costs is affected by a large number of uncertainties. Therefore, it is the purpose of this paper to introduce a life-cycle analysis for the quantification of typical user costs, in a probabilistic approach. For this purpose, the analysis of a motorway bridge in Portugal is performed. The results of the case study demonstrate ...

Concurrent multi-scale modelling and updating of long-span bridges using a multi-objective optimisation technique

Abstract: This paper aims at developing an innovative technique of concurrent multi-objective optimisation for updating the multi-scale model of long-span bridges. A multi-scale model is established for the purpose of concurrently analysing the global response of the structure and nonlinear local damages in order to assess structural state and local damage evolution or deteriorating, respectively. A multi-objective optimisation technique is proposed in this work for concurrent multi-scale model updating, in which several key issues including the determination of the objective functions and constraint conditions, the multi-objective optimisation algorithm and how to find the optimal solution from many non-inferior solutions are studied. The proposed concurrent multi-objective optimisation technique is applied to update the initial multi-scale model of Runyang Suspension Bridge (RYSB) near Shanghai, and the updated model is validated by the data from the field tests conducted for obtaining the response in global (dyn...

Non-destructive parametric system identification and damage detection in truss structures by static tests

Abstract: This article presents theoretical background, computational implementation and numerical applications of a study devoted to the non-destructive parametric identification of truss structures by means of static load tests. The proposed methodology determines the (residual) stiffness of the bars. Therefore, it detects the elements with global or localised damages and assesses the extent of damage in terms of stiffness loss. A novelty introduced by the proposed technique is the ability to take into account plane and three-dimensional structures, both statically determinate and indeterminate. Moreover, when only a partial set of measurements is available, the procedure uses genetic algorithms to overcome the lack of information. Five numerical applications are collected to prove the capabilities of the proposed methodology and to exemplify the procedure.

Probabilistic modelling of the bond deterioration of fully-grouted rock bolts subject to spatiotemporally stochastic corrosion

Abstract: Developing predictive models for quantitative assessment of the deterioration of rock bolts exposed to corrosive environments is essential for rational planning of maintenance activities for anchorage structures. This article presents a probability-based computational model for predicting the time-dependent deterioration of bond capacity of corroding rock bolts due to the attack of chlorides. The inherent stochastic nature involved in the corrosion and degradation process is identified and simulated. A method is developed based on fundamental Mohr–Coulomb theory to evaluate the effect of corrosion on the bond strength due to a failure mode involving splitting of grout cover. Parameters affecting both strength and stress state at the bolt–grout interface are quantitatively related to the degree of corrosion. Integrating the realised corrosion stochastic process and the developed bond loss evaluation method, a computational algorithm based on Monte Carlo simulation is presented for evaluating the bond deter...

Curbing rework in offshore projects: systemic classification of risks with dialogue and narratives

Abstract: Rework arises in offshore projects due to errors and omissions, and this can significantly contribute to project cost and cause schedule overruns. Indeed, these additional and unnecessary costs can uncontrollably spiral to account for 25% of capital expenditure for offshore platform projects. Yet rework costs are frequently dismissed as isolated and rare instances of unfortunate circumstances and alien to normal practice. Original evidence stemming from this research indicates that cost and schedule overruns are a recurrent feature of offshore projects. Moreover, the risk of overruns are further exacerbated by increasingly complex commercial and contracting arrangements, technical challenges, changing local economic and regulatory conditions, and a shift towards projects being undertaken in peak oil frontier regions. To acquire new knowledge on the dynamics of offshore rework, the experiences of 23 oil and gas industry practitioners were captured using in-depth interviews. A risk classification matrix was...

Optimal passive and semi-active control of a wind excited suspension bridge

Abstract: Herein, a model of an existing suspension bridge is developed at the numerical level in the ANSYS finite element code starting from original data, and it is used (a) to simulate the structural response under strong wind excitation; (b) to assess the efficacy for the bridge protection of passive and on/off Skyhook semi-active control laws, here presented in a modified version, with due attention on their feasibility and reliability. Their efficacy is shown and the factors contributing to their positive performance are highlighted. Wind loading, corresponding to the extreme event, derives from generated 3D turbulent wind fields, non-homogeneous in space to consider the atmospheric boundary layer.

Systemic life cycle design error reduction model for construction and engineering projects

Abstract: Design errors have resulted in a plethora of catastrophic building and engineering failures, and some cases have caused death and injury to workers and members of the public. Despite continued efforts to improve project performance, errors remain a significant problem due to recurrent error- traps that prevail at the people, organisational and project levels. In addressing the need to reduce error, a systemic model that is grounded in practice and the aggregated views of 46 practitioners who were interviewed about the nature and prevention of design errors is proposed. The developed model can be used to identify and mitigate design errors as well as stimulate learning throughout a project's life cycle.