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- Safi, Mohammed, 1983-, et al.
(författare)
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Procurement of the most cost-efficient bridge through incorporating LCCA with BMSs : Case-Study of the Karlsnäs Bridge in Sweden
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Ingår i: Journal of Bridge Engineering. - 1084-0702 .- 1943-5592.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Life-cycle cost analysis (LCCA) has recognized potential for rationalizing bridge procurement, but its use in this context is far from systematic and the integration of LCCA findings in decisions is often far from robust. Furthermore, although most bridge management systems (BMSs) include databases of relevant information, agencies do not use them effectively to improve future bridge investment decisions. This paper introduces a comprehensive approach for agencies to exploit their BMS to procure the most cost-efficient bridge design through fair design-build (D-B) tendering processes. The approach incorporates use of a novel LCCA technique, LCC Added-Value Analysis, that can be conveniently integrated with public agencies’ established procurement procedures and maintains contractors’ freedoms in D-B processes. The proposed approach allows bridge procurers to establish monetary LCC-efficient benchmarks and embed them in tender documents as core specifications. Hence the lowest LCC bid can be employed as the contract award criterion, rather the lowest bid in initial investment terms. The Swedish Transport Administration has recently procured several bridges using the approach, thereby gaining considerable cost savings. A presented case-study provides insights into various aspects of bridges’ LCC and illustrates analytical steps that other agencies could apply in bridge procurement.
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- Safi, Mohammed, et al.
(författare)
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Integration of life-cycle cost analysis with bridge management systems: case study of the Swedish bridge and tunnel management system.
- 2012
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Ingår i: Transportation Research Record. - : SAGE Publications. - 0361-1981 .- 2169-4052. ; :2292, s. 125-133
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Tidskriftsartikel (refereegranskat)abstract
- Many countries use bridge management systems (BMSs), and many of these systems involve some form of life-cycle cost (LCC) analysis. Use of LCC analysis in bridge engineering is rare, however; the technique has been applied primarily in the operation phase to support decisions about bridges that already exist. Yet LCC analysis can be applied across the life of a bridge. This paper introduces the Swedish Bridge and Tunnel Management System (BaTMan). A comprehensive, integrated LCC implementation scheme takes into account the bridge investment and management processes in Sweden. The basic economic analytical tools as well as other helpful LCC analysis techniques are described. A case study demonstrates improvements in BaTMan as a factor in the decision whether to repair or to replace a bridge. Cost records for 1,987 bridges were used as input data in the case study. On the basis of the same records, the average real and anticipated initial costs of various bridge types in Sweden are presented schematically.
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- Du, Guangli, 1985-, et al.
(författare)
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Life cycle assessment as a decision support tool for bridge procurement : environmental impact comparison among five bridge designs
- 2014
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Ingår i: The International Journal of Life Cycle Assessment. - : Springer Science and Business Media LLC. - 0948-3349 .- 1614-7502. ; 19:12, s. 1948-1964
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Tidskriftsartikel (refereegranskat)abstract
- The conventional decision-making for bridges is mostly focusing on technical, economical, and safety perspectives. Nowadays, the society devotes an ever-increased effort to the construction sector regarding their environmental performance. However, considering the complexity of the environmental problems and the diverse character of bridges, the related research for bridge as a whole system is very rare. Most existing studies were only conducted for a single indicator, part of the structure components, or a specific life stage. Life Cycle Assessment (LCA) is an internationally standardized method for quantifying the environmental impact of a product, asset, or service throughout its whole life cycle. However, in the construction sector, LCA is usually applied in the procurement of buildings, but not bridges as yet. This paper presents a comprehensive LCA framework for road bridges, complied with LCA ReCiPe (H) methodology. The framework enables identification of the key structural components and life cycle stages of bridges, followed by aggregation of the environmental impacts into monetary values. The utility of the framework is illustrated by a practical case study comparing five designs for the Karlsnas Bridge in Sweden, which is currently under construction. This paper comprehensively analyzed 20 types of environmental indicators among five proposed bridge designs, which remedies the absence of full spectrum of environmental indicators in the current state of the art. The results show that the monetary weighting system and uncertainties in key variables such as the steel recycling rate and cement content may highly affect the LCA outcome. The materials, structural elements, and overall designs also have varying influences in different impact categories. The result can be largely affected by the system boundaries, surrounding environment, input uncertainties, considered impact indicators, and the weighting systems applied; thus, no general conclusions can be drawn without specifying such issues. Robustly evaluating and ranking the environmental impact of various bridge designs is far from straightforward. This paper is an important attempt to evaluate various designs from full dimensions. The results show that the indicators and weighting systems must be clearly specified to be applicable in a transparent procurement. This paper provides vital knowledge guiding the decision maker to select the most LCA-feasible proposal and mitigate the environmental burden in the early stage.
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- Neves, Cláudia, 1991-
(författare)
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Structural Health Monitoring of Bridges : Model-free damage detection method using Machine Learning
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This is probably the most appropriate time for the development of robust and reliable structural damage detection systems as aging civil engineering structures, such as bridges, are being used past their life expectancy and beyond their original design loads. Often, when a significant damage to the structure is discovered, the deterioration has already progressed far and required repair is substantial. This is both expensive and has negative impact on the environment and traffic during replacement. For the exposed reasons the demand for efficient Structural Health Monitoring techniques is currently extremely high. This licentiate thesis presents a two-stage model-free damage detection approach based on Machine Learning. The method is applied to data gathered in a numerical experiment using a three-dimensional finite element model of a railway bridge. The initial step in this study consists in collecting the structural dynamic response that is simulated during the passage of a train, considering the bridge in both healthy and damaged conditions. The first stage of the proposed algorithm consists in the design and unsupervised training of Artificial Neural Networks that, provided with input composed of measured accelerations in previous instants, are capable of predicting future output acceleration. In the second stage the prediction errors are used to fit a Gaussian Process that enables to perform a statistical analysis of the distribution of errors. Subsequently, the concept of Damage Index is introduced and the probabilities associated with false diagnosis are studied. Following the former steps Receiver Operating Characteristic curves are generated and the threshold of the detection system can be adjusted according to the trade-off between errors. Lastly, using the Bayes’ Theorem, a simplified method for the calculation of the expected cost of the strategy is proposed and exemplified.
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- Allahvirdizadeh, Reza, et al.
(författare)
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Ensemble Meta-Models for Running Safety Assessment ofHigh-Speed Railway Bridges Considering Soil-StructureInteraction Effects
- 2022
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Konferensbidrag (refereegranskat)abstract
- Increasing operating speeds and axle loads of trains may induce higher verticaldeck accelerations on bridges, which may subsequently lead to the occurrence of ballast instabilities.This phenomenon not only increases maintenance costs but also leads to speed restrictionsunder operating conditions. In severe cases, it can also cause train derailment. Thishas been shown to be the governing criterion for the design of short to medium span lengthhigh-speed railway bridges, especially from the dynamic behaviour point of view. Despiteits substantial importance in the design of railway bridges, the conventional deterministic approachescannot achieve the desired level of safety (Allahvirdizadeh et al. 2020). Therefore,this article is devoted to the evaluation of the probability of violating running safety usingsimulation-based methods. In this context, different variables, including those for the bridge(span length, flexural rigidity, and geometric properties), for the train (axle load, dominantfrequency and damping ratio) and for the boundary conditions (soil and foundation properties)are considered. Due to the high computational cost and complexity of the consideredperformance function, a low-cost meta-model is trained using stack modelling concept as acombination of support vector machines (SVM), k-nearest neighbours (k-NN) and decisiontrees. Then, the range of maximum and minimum probabilities of exceeding the verticalacceleration threshold are evaluated as a function of train speed and bridge span length. Comparingthese boundaries with corresponding results of simply-supported bridges showed thatneglecting soil-structure interaction effects in shorter span bridges may result an underestimatedsafety of the system; however, for longer span bridges it may result in overestimatedsafeties.
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- Allahvirdizadeh, Reza
(författare)
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Improving the Dynamic Design Philosophy of High-Speed Railway Bridges Using Reliability-Based Methods
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Modern railway infrastructures, especially bridges, are exposed to significant vibrations with potential safety implications. In this context, previous studies have shown the inconsistency and inadequacy of some conventional design methods necessitaing them to be improved. The assessment of safety inherently deals with uncertainties. Therefore, the current study is dedicated to this objective using reliability-based methods. Of the various possible failure modes, the investigations presented here are limited to running safety and passenger comfort. The investigation of these limit-states requires constructing complex computational models with train-track-bridge interaction capabilities. However, the application of these computationally intensive models in the context of structural reliability does not appear to be feasible. Simplifying the system, the vertical acceleration and the deflection of the bridge serve as implicit limit-state measures. Initially, using First Order Reliability Method (FORM) revealed limitations in the application of the current safety factor, resulting in inconsistent reliability indices. Therefore, probabilistic design curves are proposed, defining minimum required bridge mass and stiffness based on cross-section types, span configurations and train speeds. These results are obtained by formulating a FORM-based optimization. Subsequently, the results are used to investigate the sensitivity of the estimated failure probabilities with respect to the contributing basic random variables. Acknowledging the limitations of FORM, surrogate-assisted simulation-based reliability assessments were used for further investigations. A comparison of the performance of widely used regression-based surrogate models under an identical active learning scheme showed the superior performance of the Kriging method over the others. Within areliability-based design optimization framework, this Kriging model facilitates the generation of new probabilistic design curves. This is achieved by reformulating the conventional method to account for the dependency between design variables using the copula concept. In addition, the surrogate model aided in calibrating the safety factor associated with the vertical acceleration threshold, leading to a proposal of 1.38 as a new safety factor. Subsequently, the influence of soil-structure interaction on the estimated reliability indices is evaluated using an ensemble of classification-based surrogate models. Results highlighted its beneficial contribution in terms of increased damping for shorter spans, countered by adverse effects due to frequency shortening in longer bridges. Finally, the epistemic uncertainties arising from the limited knowledge of the vertical acceleration threshold are investigated. It is found that neglecting these uncertainties can lead to an overestimation of allowable train speeds by about 13%.
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| 10. |
- Allahvirdizadeh, Reza, et al.
(författare)
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Minimum Design Requirements of High-Speed RailwayBridges Using Reliability-Based Design Optimization
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Constructing high-speed railway networks received a great attention during pastdecade raising new safety concerns on infrastructure (particularly bridges). It ismainly because of possible excessive vibrations due to higher operating speeds.In this regard, deficiency or vague scientific background for some of designmethodologies are shown by former studies; among which is the adopted safetyfactor for running safety. This limit state occurs if the load path from the trainto the bridge is disturbed by dislocating ballast particles because of excessivevertical accelerations of the bridge deck. Hence, the current article is devotedto update the conventional design methodology. For this objective, reliabilitybaseddesign optimization technique is employed to propose minimum allowablemass and stiffness (or maximum permissible fundamental frequency) which assuressatisfying target reliability level. This is achieved by adaptively trainingKriging meta-models to surrogate the computational models. It seems that theproposed method can result in lighter (economical) bridges in comparison tothe conventional design methodology; however, this beneficial aspect vanishesby increasing span length of the bridge.
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