Showing papers in "Structure and Infrastructure Engineering in 2007"

Maintenance and management of civil infrastructure based on condition, safety, optimization, and life-cycle cost∗

Abstract: Cost-competent maintenance and management of civil infrastructure requires balanced consideration of both the structure performance and the total cost accrued over the entire life-cycle. Most existing maintenance and management systems are developed on the basis of life-cycle cost minimization only. The single maintenance and management solution thus obtained, however, does not necessarily result in satisfactory long-term structure performance. Another concern is that the structure performance is usually described by the visual inspection-based structure condition states. The actual structure safety level, however, has not been explicitly or adequately considered in determining maintenance management decisions. This paper reviews the recent development of life-cycle maintenance and management planning for deteriorating civil infrastructure with emphasis on bridges using optimization techniques and considering simultaneously multiple and often competing criteria in terms of condition, safety and life-cycle...

A wireless structural health monitoring system with multithreaded sensing devices: design and validation

Abstract: Structural health monitoring (SHM) has become an important research problem which has the potential to monitor and ensure the performance and safety of civil structures. Traditional wire-based SHM systems require significant time and cost for cable installation. With the recent advances in wireless communication technology, wireless SHM systems have emerged as a promising alternative solution for rapid, accurate and low-cost structural monitoring. This paper presents a newly designed integrated wireless monitoring system that supports real-time data acquisition from multiple wireless sensing units. The selected wireless transceiver consumes relatively low power and supports long-distance peer-to-peer communication. In addition to hardware, embedded multithreaded software is also designed as an integral component of the proposed wireless monitoring system. A direct result of the multithreaded software paradigm is a wireless sensing unit capable of simultaneous data collection, data interrogation and wirele...

A modified shuffled frog-leaping optimization algorithm: applications to project management

Abstract: Evolutionary algorithms, such as shuffled frog-leaping, are stochastic search methods that mimic natural biological evolution and/or the social behavior of species. Such algorithms have been developed to arrive at near-optimum solutions to complex and large-scale optimization problems which cannot be solved by gradient-based mathematical programming techniques. The shuffled frog-leaping algorithm draws its formulation from two other search techniques: the local search of the ‘particle swarm optimization’ technique; and the competitiveness mixing of information of the ‘shuffled complex evolution’ technique. A brief description of the original algorithm is presented along with a pseudocode and flowchart to facilitate its implementation. This paper then introduces a new search-acceleration parameter into the formulation of the original shuffled frog-leaping algorithm to create a modified form of the algorithm. A number of simulations are carried out for two continuous optimization problems (known as benchmar...

Design of a structural health monitoring system for long-span bridges

Abstract: Structural health monitoring systems (SHMSs) have been adopted over the past decade to monitor and evaluate the structural health condition of long-span bridges. A SHMS is currently included as a standard mechatronic system in the design and construction of most large-scale and multi-disciplinary bridge projects, such as Stonecutters Bridge and SuTong Bridge in Hong Kong and China. The modular concept used in the design of the SHMSs for Tsing Ma Bridge, Kap Shui Mun Bridge and Ting Kau Bridge has a significant influence on the design of new SHMSs in Hong Kong and China. This modular concept has, however, been enhanced in the detailed design of the SHMS for Stonecutters Bridge by the Highways Department of Hong Kong. This paper introduces the enhanced modular concept of six integrated modules in terms of their respective functional performance requirements. The six integrated modules are the sensory system, the data acquisition and transmission system, the data processing and control system, the structural...

Investigation of reliability method formulations in DAKOTA/UQ

Abstract: Reliability methods are probabilistic algorithms for quantifying the effect of simulation input uncertainties on response metrics of interest. In particular, they compute approximate response function distribution statistics (probability, reliability and response levels) based on specified input random variable probability distributions. In this paper, a number of algorithmic variations are explored for both the forward reliability analysis of computing probabilities for specified response levels (the reliability index approach (RIA)) and the inverse reliability analysis of computing response levels for specified probabilities (the performance measure approach (PMA)). These variations include limit state linearizations, probability integrations, warm starting and optimization algorithm selections. The resulting RIA/PMA reliability algorithms for uncertainty quantification are then employed within bi-level and sequential reliability-based design optimization approaches. Relative performance of these uncert...

Simplified site-specific traffic load models for bridge assessment

Abstract: Traffic load is identified as one of the greatest sources of uncertainty in the assessment of bridges. In recent years, simulation techniques, using measured traffic data, have been used to predict the characteristic traffic load effects on bridges. However, the techniques are complex, sensitive to the assumptions adopted and require specialist statistical expertise. This work presents a simplified site-specific traffic load model that generates comparable load effects to the corresponding results from a full simulation. While the simplified model is still sensitive to the underlying assumptions, these can be carefully reviewed prior to the method being approved. Further, the simplified method can be employed by practising engineers for bridge assessment.

Assessment of existing steel structures. A guideline for estimation of the remaining fatigue life

Abstract: In many countries and regions, traffic infrastructure projects suffer from low funding. The budget is tight for new infrastructure building and, thus, the importance of inspection, maintenance and assessment of the existing traffic infrastructure increases. A new fatigue assessment guideline for the estimation of the remaining fatigue life of steel bridges has been written by technical committee 6 of the European Convention of Constructional Steelwork (ECCS). It will be a useful tool for the complementation of bridge management systems, used commonly for condition assessment. Design specifications and rules are harmonised throughout Europe. They are under constant development, but there is still a lack of forwarding and concentrating experiences as well as developing rules for the fatigue assessment on existing steel structures. This paper presents a guideline with a proposed fatigue assessment procedure for existing steel structures embedded in information about old materials and non-destructive testing ...

A reliability-based bridge management concept

Abstract: Since 2004, the Autonomous Province of Trento, Italy, has adopted a Bridge Management System entirely based on reliability concepts. The system operates on the web, and includes sections for (1) condition state evaluation, (2) safety assessment, and (3) prioritization. Condition appraisal is based on visual inspections, and acknowledges the general rules of the AASHTO Commonly Recognized Standard Element system. Normally, the system conservatively estimates the prior reliability of each bridge, based on the sole inspection data. Where the condition of the bridge gives cause for concern, its reliability is evaluated in a more formal manner using multi-step procedures of increasing refinement. Decision-making is driven by a principle whereby priority is given to those actions that, within a certain budget, will minimize the risk of occurrence of an unacceptable event in the whole network. In this paper, the operation of the system is illustrated, with the support of a number of practical cases.

The risk-return tradeoff in optimizing regional earthquake mitigation investment

Abstract: Earthquakes are low probability-high consequence events, regional earthquake mitigation is therefore a risky investment. Despite its importance, the risk-return tradeoff is often not examined explicitly in regional earthquake risk management resource allocation decisions. This paper introduces a stochastic optimization model developed to help decision-makers understand the risk-return tradeoff in regional earthquake risk mitigation, and to help state and local governments comply with the Disaster Mitigation Act of 2000 requirement that they develop a mitigation plan. Taking advantage of the special structure of the optimization, Dantzig-Wolfe decomposition is used as the solution method. A case study for Central and Eastern Los Angeles illustrates an application of the model. Results include a graph of the tradeoff between risk and return, quantification of the relative contributions of each possible earthquake scenario, and discussion of the effect of risk aversion on the selection of mitigation alternat...

Neural network prediction of concrete degradation by sulphuric acid attack

Abstract: Microbiologically induced corrosion is a leading cause of the deterioration of wastewater collection, transmission and treatment infrastructure around the world. This paper examines the feasibility of using artificial neural networks (ANNs) to predict the compressive strength of concrete and its degradation under exposure to sulphuric acid of various concentrations. A database incorporating 78 concrete mixtures performed by the authors was developed to train and test the ANN models. Data were arranged in a patterned format in such a manner that each pattern contains input variables (concrete mixture parameters) and the corresponding output vector (weight loss of concrete by H2SO4 attack and compressive strength at different ages). Results show that the ANN model I successfully predicted the weight loss of concrete specimens subjected to sulphuric acid attack, not only for mixtures used in the training process, but also for new mixtures unfamiliar to the ANN model designed within the practical range of the...

Beneficial impact of coatings on biological generation of sulfide in concrete sewer pipes

Abstract: Hydrogen sulfide is a serious problem for many municipalities across North America and worldwide. Odor, safety, and corrosion are the major problems associated with the presence of hydrogen sulfide in sewerage systems. This paper investigates the effect on sulfide generation of using innovative coatings in concrete sewer pipes. A pilot-scale model, consisting of three concrete pipes (each 75 cm in length and 30 cm in internal diameter), was used to simulate the process of sulfide generation in a sewer system. Two of the pipes were internally coated with either cuprous oxide (C.O) or silver oxide (S.O), while the third one served as a control. Each of the oxides was mixed with a commercial epoxy, used for repairing concrete sewer pipes, prior to spraying on the internal surface of the concrete pipe specimens to form a coating film. Test data showed that the sulfide generation by sulfate-reducing bacteria (SRB) in the C.O and S.O coated pipes was reduced by 92% and 100%, respectively, compared with that of ...

Priority ranking towards condition assessment of existing reinforced concrete bridges

Abstract: Existing old bridges in most countries were designed for less traffic and are inadequate to carry current-day traffic and satisfy the present codal provisions. Even for newer bridges, deterioration caused by unforeseen service conditions and deferred maintenance is causing great concern to bridge engineers. Hence, there is an urgent need for a systematic methodology for priority ranking of the bridges for both their rehabilitation in the future and for the allocation of funding. In this paper, an Analytic Hierarchy Process (AHP), which is an efficient decision making tool for complicated problems with multiple evaluation criteria and uncertainty, has been proposed for the condition ranking of reinforced concrete (RC) bridges. Fuzzy logic is used to handle the subjective judgement, imprecision and intuition involved in a bridge inspector's evaluation report. This methodology would certainly help engineers and bridge management policy makers to overcome the problems related to prioritization and decisions o...

Vibration based structural health monitoring: Wavelet packet transform based solution

Abstract: One prominent problem for vibration-based structural health monitoring is to extract condition indices which are sensitive to damage and yet insensitive to measurement noise. In this paper, a condition index extraction method based on the wavelet packet transform (WPT) is proposed. This transform leads to the formulation of a novel condition index: wavelet packet signature (WPS). The sensitivity of the WPS to the change of structural parameters is derived and validated on a five-degrees-of-freedom spring-mass system. Results show that the WPS is significantly more sensitive to the stiffness change than the natural frequencies and the mode shapes. Its sensitivity is slightly better or comparable to that of the modal flexibility matrices depending on the location of damage. A variability analysis is also performed to study the effect of measurement noise on the proposed WPS. Results show that the WPS does not show any significant variation even under the presence of 10 dB noise. To illustrate the potential ...

Effect of thermal stresses on mid-slab cracking in dowel jointed concrete pavements

Abstract: Mid-slab cracking is considered to be one of the main causes of pavement deterioration and enormous funds are spent each year on repairing and maintaining cracked pavements. In this study, a nonlinear three-dimensional finite element (3DFE) analysis, which includes detailed consideration of slab constraints by dowel bars, is used to analyse the problem of premature transverse cracking in jointed concrete pavements. The 3DFE model response to ambient temperature variations is validated versus field-measured data obtained from instrumented concrete slabs constructed in Goshen Road near Morgantown, West Virginia, USA. The modelling results indicate that the combination of ambient temperature drop and slab curling induces slab constraints that lead to the development of mid-slab transverse cracks. The slab length is shown to be a critical parameter that governs the magnitude of the maximum thermal stress induced at maximum mid-slab. It is shown in this paper that 4.57 m is the optimal slab length to avoid mid...

Bridge owner's benefits from probabilistic approaches

Abstract: The growth of national economies in the latter half of the twentieth century has resulted in steadily increasing traffic volumes on trading routes and in an increase in the demands placed on an ageing bridge stock. Ironically, economic growth has not resulted in an increase in the budgets available to bridge owners for maintenance of their ageing resource. The approach adopted by the Danish Road Directorate in addressing this challenge has been to exploit advances in scientific methods in the management of its bridges. The use of probabilistic approaches within the areas of capacity assessment of bridges, bridge management and ship impact assessments have resulted in substantial cost savings, and future maintenance and repair needs have been minimized. Examples of the various areas where the probabilistic approaches have been applied are given, and both the technical approach and the administrative and financial benefits are presented.

Present condition of highway bridges in Vietnam: an analysis of current failure modes and their main causes

Abstract: This paper reports on research conducted to evaluate the current status of highway bridges in Vietnam. The adopted approach included literature reviews to identify common failure modes and causes, together with site inspections to ascertain their validity. Interviews were also conducted with the various stakeholders to further understand the current condition of the inspected bridges. Results show an overall picture of existing bridges in poor physical condition, thus providing poor service to users. Defects that have previously been identified in the literature include corrosion, settlement, fatigue damage, obsolescence, scouring and aging. New problems identified were human invasions and missing elements. Previous literature identifies traffic overload and jams, collision, adverse environmental conditions and poor maintenance as causes for these problems. Additionally, this paper considers war, improper data retention and other country-specific causes. The authors suggest that maintenance efforts should...

A model for life cycle evaluation of highway investments

Abstract: Sustainable development has added a new dimension to the evaluation of highway capacity investments. It places an emphasis on analyzing the entire life of a facility, from an environmental as well as an economic perspective. This paper presents a way to analyze capacity investments that is consistent with the sustainable development perspective. It departs from the typical approach of focusing on a small set of peak use conditions, often in the design year. It couples economic concepts with a representation of the facility's lifetime use to perform a robust analysis. A freeway facility is used to illustrate the ideas. Principles of engineering economics and life cycle costing help determine what incremental capacity investments would be warranted given postulated or observed use patterns. It is then demonstrated that the findings from this analysis and the principles employed can be applied to a wide range of infrastructure investment decision making situations.

Finite element reliability analysis of chloride ingress into reinforced concrete structures

Abstract: For many reinforced concrete structures corrosion of the reinforcement is an important problem since it can result in maintenance and repair actions. Further, a reduction of the load-bearing capacity can occur. In the present paper the Finite Element Reliability Method (FERM) is employed for obtaining the probability of exceeding a critical chloride concentration level at the reinforcement bars, both using Monte Carlo Simulation (MCS) and the First Order Reliability Method (FORM). The chloride ingress is modelled by the Finite Element Method (FEM) and the diffusion coefficient, surface chloride concentration and reinforcement cover depth are modelled by stochastic fields, which are discretized using the Expansion Optimum Linear Estimation (EOLE) approach. The response gradients needed for FORM analysis are derived analytically using the Direct Differentiation Method (DDM). As an example, a bridge pier in a marine environment is considered and the results are given in terms of distributions of time for ini...

Investigation of the applicability of current bridge health monitoring technology

Abstract: Integrated health monitoring (HM) systems have been designed and installed in some long-span bridges around the world. One of the fundamental objectives of a bridge HM system is to gain a comprehensive knowledge of the structural condition, and usually it is required that early-stage damage in a bridge is detected within the monitored information. Yet the performance of the HM technology has not been evaluated in practice. The focus of this paper is to investigate the applicability of the current bridge HM technology for abnormality alarming. The deterioration and defects found from 16 cable-stayed bridges are summarized, and possible damage scenarios are simulated with a finite element model of a cable-stayed bridge. The changes in the static deformation and stress distribution as well as the dynamic characteristics of the bridge model due to damage are analysed. By comparison of the damage-caused changes in the structural behavior with the ability of the current monitoring techniques and the environment...

A life-cycle capacity-based approach to allocating investments in municipal sanitation infrastructure

Abstract: The lack of access to water and sanitation services is a well-acknowledged problem that affects more than 40% of the world's people, who live in its poorest communities. Providing sustained access to infrastructure services in these communities requires approaches that build local capacity to acquire, build, and manage the systems that provide these services. This paper presents a pedagogical model that spans the lifecycle of sanitation infrastructure acquisition by communities with chronic inaccessibility to water and sanitation services. The pedagogy consists of community capacity assessment, service technology systems evaluation, and sequential allocation of capital investments to expand the capacity for water supply, wastewater and sewage treatment, and solid waste management infrastructure in affected communities. The allocation sequence covers a system lifecycle that allows the deficit in services in a community to be reduced to an acceptable minimum.

An approach to modelling concrete bridge condition deterioration using a statistical causal relationship based on inspection data

Abstract: While physical models of concrete structures may give a fundamental understanding of structural deterioration mechanisms, their application is more or less limited in reflecting actual scenarios as a result of inevitable theoretical assumptions, whereby it is often difficult to cover complex structural behaviour and environment in the real world. Uncertainties and fuzziness, along with complexity, add more difficulty to the estimation of structural deterioration by physical models, which are typically described by quantitative mathematical equations. To complement physical models, an approach based on a statistical causal relationship, combining logics and statistics, is established for modelling structural condition deterioration. The relationship includes three kinds of basic variables in terms of causal factors, consequences and indicators, and it is represented by a set of conditional probabilities among those variables. Level two inspection data on concrete bridge slabs, as an example, is ap...

Rehabilitation assessment of a steel railway bridge by dynamic field testing

Abstract: The seven-span steel railway bridge crossing the River Nile near Qanater, Egypt, has been reported to have excessive sway under the current railway traffic loads. A rehabilitation plan has been made previously to preserve and enforce the structural condition of this main bridge. Dynamic testing techniques were used here to evaluate the modal properties of the bridge system at different stages of the repair plan. Ambient vibration measurements together with measurements after the passage of trains were conducted. The dynamic parameters of the bridge were extracted using both the Frequency Domain Decomposition (FDD) and the Eigen Realization Algorithm (ERA) techniques. Comparisons were made to understand the basic behaviour of the bridge and to evaluate the effectiveness of the current repair method. The modification in the stiffness of the bridge due to rehabilitation was evaluated. The current rehabilitation strategy proved effective; as a result of this study, further recommendations are made.

Health monitoring data in assessing critical behaviour of bridges

Abstract: A baseline finite element model has been developed and used for system identification of the Confederation Bridge in Canada. The model was calibrated using the test data collected by the health monitoring system during two field tests. The frequencies and mode shapes obtained from the modal analyses were in good agreement with the values obtained from the tests. The model was used to simulate the bridge responses to the field tests. Continuity of the bridge model beyond the baseline model is essential in analysing its behaviour under moving truck loads. Coupling of the longitudinal movements of the pier tops with vertical movement of the deck and rocking vibration of the drop-in girders were observed in modal analyses of the extended model, which was then used for seismic analyses. The possibility of slippage of the drop-in girder as well as its separation from the bearings during strong ground motions should be considered in designing and future extension of the instrumentation program and the analyses o...

Time-variant reliability of retaining walls and calibration of partial factors

Abstract: A methodology for the time-variant reliability analysis of geotechnical structures, particularly retaining walls, is presented. Calculation of the reliability of a wall, at any time during its lifetime, is enabled through the consideration of the degradation of soil shear strength parameters with time. In addition, the effects of spatial variability and model uncertainty are accounted for. Following an initial application with regard to British and European design standards, the methodology is extended in order to enable the calibration of partial factors for design to Eurocode 7. It is concluded that the values recommended for these factors are excessively high, at least for temporary structures that should be designed to withstand loads for just a few years. Therefore, a procedure for calculating reduced values of the partial factors that correspond to an appropriate safety level is further proposed.

Rethinking mega-project development strategies: A case study of the Central Artery/Tunnel Project

Abstract: For the majority of the last century, infrastructure development and management has focused primarily upon capital construction. In addition, a substantial amount of the financing for infrastructure, particularly within the US, has come from federal sources as evidenced by the Interstate Highway System Program and the EPA Construction Grants Program. The proclivity to focus upon the capital development cycle and the reliance upon federal funding have generally limited innovation in approaches to infrastructure development and minimized the importance of lifecycle management. However, new methods for both delivering and financing infrastructure have experienced a rebirth over roughly the last two decades. Integrated delivery strategies such as design-build-operate have increased the emphasis upon viewing constructed facilities as systems and have forced the recognition that sustaining these facilities requires more than just the initial capital investment. Unfortunately, new delivery and financing techniqu...

An approach for optimizing pavement design–redesign parameters in PPP projects

Abstract: Modeling the elasticity modulus of unbound granular pavement materials has attracted significant research interest because of its importance in pavement design particularly in PPP/BOT projects. These efforts have been hampered by three factors: (i) inability to capture the correlations between the asphalt and granular layers and the subgrade, (ii) inadequate modeling of the effects of external factors on the elasticity modulus of unbound materials, and (iii) widespread use of linear statistical relationships to model a complex and non-linear phenomenon. In this paper genetically optimized neural networks and falling weight deflectometer (FWD) back-analysis results from a newly constructed BOT project in Athens, Greece, are employed in order to evaluate pavement section design parameters. It is shown that parameter values adopted during design do not co-inside with those observed from the back-analysis studies. Further, the results indicate that the relative estimation error for the modulus of elasticity o...

Verification of thermal restraint of a railways trough structure by long-term monitoring

Abstract: At the central railway station of Berlin a trough structure was erected to extend the tracks from the underground station to ground level. The trough is subjected to high ground water pressure. Safety against up-lift called for the coupling of the trough with the underwater concrete slab and the back-anchorage of the structure by piles. Such coupling leads to high restraint due to hydration of the concrete and the ambient weather. Analysis required assumptions regarding the interaction between the trough and the impeding sub-structure, as well as the stipulation of load-independent design actions based on meteorological studies. The owner decided to install a long-term monitoring system in order to verify the thermal and mechanical response of the structure. However, the main goal of monitoring is the improvement of specifications for design and tender of future structures with comparable complexity. The program and the monitoring techniques will be described, and specific results will be reported. Prelim...

Structure and Infrastructure Engineeringacceptance in the science citation index

Abstract: We are pleased to announce that Structure and Infrastructure Engineering has been accepted by Thomson ISI for inclusion in the Science Citation Index. The title will be added to both the Science Citation Index Expanded (Web of Science) and the Current