| 1. |
- Björnsson, Ivar, et al.
(författare)
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Decision support framework for bridge condition assessments
- 2019
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Ingår i: Structural Safety. - : Elsevier BV. - 0167-4730 .- 1879-3355. ; 81
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Tidskriftsartikel (refereegranskat)abstract
- An essential aspect in the maintenance of existing bridges is the ability to adequately and accurately assess and evaluate the condition of the structure. Condition assessments, which can be carried out in any number of ways, provide valuable information concerning the actual state of a bridge, including the severity of potential damages, and form the basis for further maintenance decisions. Any decision support concerning the management of existing structures thus requires attention towards the uncertainties associated with the assessment methods when applied in practice as well as the maintenance actions these support. These uncertainties cannot be solely described as model uncertainties but are also a result of the variation in engineering performance observed in practice. In the current paper a rational and systematic framework is presented which provides practical decision support concerning whether condition assessments are necessary, what assessment methods are recommended, if invasive actions are needed, or if some other non-invasive option may be more appropriate. The framework takes into account three main attributes of an enhanced condition assessment, namely, modelling sophistication, considerations of uncertainties and risks, and knowledge/information content. Increasing the level of one or more of these attributes may be advantageous only if the expected benefits or added value of information is considered appropriate in relation to the cost of implementation in practice. A decision making model, based on Bayesian decision theory, is adopted to evaluate this problem. Two case studies, in which the framework is applied, are provided for illustrative purposes; the first is a generic numerical example and the second a decision scenario related to the fatigue assessment of an existing railway bridge.
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| 2. |
- Hingorani, Ramon, et al.
(författare)
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Consequence classes and associated models for predicting loss of life in collapse of building structures
- 2020
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Ingår i: Structural Safety. - : Elsevier B.V.. - 0167-4730 .- 1879-3355. ; 85
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Tidskriftsartikel (refereegranskat)abstract
- Most building design codes distinguish structural reliability levels in terms of failure consequences, for which they normally define consequence classes based on building type and use. Although readily applicable in everyday practice, that approach may entail adopting inconsistent safety requirements. Such a significant drawback could be minimised by establishing separate reliability levels for key members on the grounds of the potential consequences of their collapse. Further to those concerns, this paper proposes a series of consequence classes determined in keeping with the number of persons at risk in a given collapse scenario and the extent of the respective damage. Consequence class-related models for predicting loss of life are derived from statistical assessments of data on over 150 collapsed buildings. The models developed estimate the number of fatalities and conditional probability of death of building users under given collapse circumstances. In addition to their utility in establishing target reliability values, these models can be applied in risk analysis of specific building structures, especially where the potential consequences of failure are high.
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| 3. |
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| 4. |
- Maljaars, Johan, et al.
(författare)
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Models and methods for probabilistic safety assessment of steel structures subject to fatigue
- 2024
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Ingår i: Structural Safety. - : Elsevier BV. - 0167-4730 .- 1879-3355. ; , s. 102446-102446
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Tidskriftsartikel (refereegranskat)abstract
- We review of the state of the art in probabilistic modelling for fatigue reliability of civil engineering and offshore structures. The modeling of randomness and uncertainty in fatigue resistance and fatigue load variables are presented in some detail. This is followed by a review of the specifics of reliability analysis for fatigue limit states and a background on the semi-probabilistic treatment of fatigue safety. We discuss the different life-cycle reliability concepts and give an overview on probabilistic inspection planning. We describe the choices made in the Probabilistic Model Code of the Joint Committee of Structural Safety, present alternatives to these choices and suggest areas of future research.
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| 5. |
- Spross, Johan, 1986-, et al.
(författare)
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Reliability-based alarm thresholds for structures analysed with the finite element method
- 2019
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Ingår i: Structural Safety. - : Elsevier. - 0167-4730 .- 1879-3355. ; 76, s. 174-183
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Tidskriftsartikel (refereegranskat)abstract
- Civil engineering structures are commonly monitored to assess their structural behaviour, using alarm thresholds to indicate when contingency actions are needed to improve safety. However, there is a need for guidelines on how to establish thresholds that ensure sufficient safety. This paper therefore proposes a general computational algorithm for establishment of reliability-based alarm thresholds for civil engineering structures. The algorithm is based on Subset simulation with independent-component Markov chain Monte Carlo simulation and applicable with both analytical structural models and finite element models. The reliability-based alarm thresholds can straightforwardly be used in the monitoring plans that are developed in the design phase of a construction project, in particular for sequentially loaded structures such as staged construction of embankments. With the reliability-based alarm thresholds, contingency actions will only be implemented when they are needed to satisfy the target probability of failure.
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| 6. |
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| 7. |
- Spross, Johan, 1986-, et al.
(författare)
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When is the observational method in geotechnical engineering favourable?
- 2017
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Ingår i: Structural Safety. - : Elsevier BV. - 0167-4730 .- 1879-3355. ; 66, s. 17-26
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Tidskriftsartikel (refereegranskat)abstract
- The observational method in geotechnical engineering is an acceptable verification method for limit states in Eurocode 7, but the method is rarely used despite its potential savings. Some reasons may be its unclear safety definition and the lack of guidelines on how to establish whether the observational method is more favourable than conventional design. In this paper, we challenge these issues by introducing a reliability constraint on the observational method and propose a probabilistic optimisation methodology that aids the decision-making engineer in choosing between the observational method and conventional design. The methodology suggests an optimal design after comparing the expected utilities of the considered design options. The methodology is illustrated with a practical example, in which a geotechnical engineer evaluates whether the observational method may be favourable in the design of a rock pillar. We conclude that the methodology may prove to be a valuable tool for decision-making engineers’ everyday work with managing risks in geotechnical projects.
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| 8. |
- Olsson, Anders, et al.
(författare)
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On Latin hypercube sampling for structural reliability analysis
- 2003
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Ingår i: Structural Safety. - 0167-4730. ; 25:1, s. 47-68
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Tidskriftsartikel (refereegranskat)abstract
- Latin hypercube sampling is suggested as a tool to improve the efficiency of different importance sampling methods for structural reliability analysis. In simple importance sampling, where the sampling centre is moved from the origin to the design point, standard Monte Carlo sampling can be replaced by Latin hypercube sampling. The efficiency improvement is then highly dependent on the choice of sampling directions. Different versions of Latin hypercube sampling are also successfully employed to improve the more efficient axis orthogonal importance sampling method. By means of different numerical examples, it is shown that more than 50% of the computer effort can be saved by using Latin hypercubes instead of simple Monte Carlo in importance sampling. The exact savings, however, are dependent on details in the use of Latin hypercubes and on the shape of the failure surfaces of the problems. (C) 2002 Elsevier Science Ltd. All rights reserved.
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| 9. |
- Anderson, Patrick, et al.
(författare)
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Reliability-based evaluation of the prestress level in concrete containments with unbonded tendons
- 2008
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Ingår i: Structural Safety. - : Elsevier BV. - 0167-4730. ; 30:1, s. 78-89
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Tidskriftsartikel (refereegranskat)abstract
- It has been a common practice both in Sweden and worldwide to enclose nuclear reactors with prestressed concrete structures. The prestress level decreases with time from its initial value due to various degradation mechanisms. To ensure that the prestress level is sufficient the tendon force is measured at regular in-service inspections. The intention with this paper is to present a reliability-based procedure to evaluate the prestress level on the basis of data from in-service inspections. Existing approaches to evaluate the prestress level do not take into account the variability in the measured prestress. It is not possible to achieve a complete assurance concerning the prestress level. However, by using a probabilistic model, involving the variability in the measuring result and the structural behaviour, the prestress level could be confirmed in a more stringent way. Both the time dependent loss of prestress and the possibility of tendons being broken (due to defects as corrosion) are considered. To avoid through-wall cracks in the concrete it is required that the prestress shall counterbalances the tensile stresses expected at an internal accident. The factor of interest is the prestress level in the concrete and not the force in individual tendons. Several tendons influence the prestress level in a specific part of the containment. The required prestress level shall be fulfilled in all parts of the containment where each part is influenced by a number of individual tendons. It is suggested in this paper that this problem can be analysed as a structural reliability problem idealized as a series of correlated parallel subsystems. (C) 2006 Elsevier Ltd. All rights reserved.
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| 10. |
- Fröderberg, Martin, et al.
(författare)
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Uncertainty caused variability in preliminary structural design of buildings
- 2015
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Ingår i: Structural Safety. - : Elsevier BV. - 0167-4730. ; 52, s. 183-193
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- Many decisions in the everyday work of the structural engineer are taken under the influence of uncertainties. The degree of uncertainty affects the quality and variability of the outcome of the structural design work. The effect of uncertainties related to knowledge and experience of the structural engineer was studied in a round robin investigation. Despite a relatively well defined task, the results varied considerably among the 16 participating Swedish structural engineers that performed this task; a structural check, load takedown and stability calculation for a five storey concrete building. The column load of a specific position differed by a factor of three between lowest and highest suggested value. For the stabilizing forces the values varied even more. The uncertainties connected to the structural engineer were estimated by introducing the term Engineering Modeling Uncertainty, divided into a structural model part and a load part. These uncertainties are shown to have a large effect on structural safety. The significant variability in results and the consequence on structural safety of this investigation emphasizes the importance of documentation and communication of all the assumptions made by the structural engineer - even the apparently obvious ones. (C) 2014 Elsevier Ltd. All rights reserved.
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| 11. |
- Honfi, Daniel
(författare)
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Serviceability floor loads
- 2014
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Ingår i: Structural Safety. - : Elsevier BV. - 0167-4730. ; 50, s. 27-38
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Tidskriftsartikel (refereegranskat)abstract
- Serviceability of structures has to be verified for a lower load level than the design load used for safety considerations. Representative values of actions used in serviceability load combinations are often defined in a way that the fraction of time spent above a given load level should be limited to a certain value. To determine these load levels more information on the stochastic nature of the loading process is needed than to estimate the design load. A convenient way in structural design codes is to express representative values (rare, frequent and quasi-permanent) as a fraction of the characteristic value by using load reduction factors. However, the characteristic value is usually defined in a different way i.e. with a certain probability of not being exceeded (in a chosen period of time). The current paper estimates representative values of floor live loads by numerical simulation using stochastic live load models with a special focus on serviceability. The results are compared to values given in existing standards (Eurocode on first place). Improvements are suggested concerning the load reduction factors, the definitions of the representative values and the stochastic load parameters. (C) 2014 Elsevier Ltd. All rights reserved.
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| 12. |
- Larsson Ivanov, Oskar, et al.
(författare)
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Climate change impact on snow loads in northern Europe
- 2022
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Ingår i: Structural Safety. - : Elsevier BV. - 0167-4730. ; 97
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Tidskriftsartikel (refereegranskat)abstract
- Ongoing and future climate change will affect our built environment. It will have an impact on how we should design our structures to withstand the future environment. One important load when designing buildings in high latitudes and high elevations is the snow load, which in many countries is the governing load for roofs and other structural parts. A warmer climate may lead to a reduction in snow cover. How this reduction relates to extreme values that occur very seldom, however, is unclear. For some regions an increase in precipitation may lead to an increase in snow fall over the winter, and thus to higher snow loads even in a warmer climate. The annual maximum snow water equivalents available from an ensemble of regional climate projections representing the three emission scenarios, RCP 2.6, RCP 4.5, and RCP 8.5, were used to project how the snow load will change in northern Europe until the end of the century. The variability between the different models is studied by analyzing results for individual cities as well as the overall regional variation. The results show that the spatial difference is large, where the mountainous and colder areas may experience an increase in extreme snow loads in the future for all climate scenarios, while the warmer parts of the region may have a significant decrease. The study shows that it is possible to project future snow loads with reasonable accuracy. The variability is still large, though, and must be considered when using climate projections for structural design.
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| 13. |
- Sanchez Heres, Luis Felipe, 1984, et al.
(författare)
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Influence of mechanical and probabilistic models on the reliability estimates of fibre-reinforced cross-ply laminates
- 2014
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Ingår i: Structural Safety. - : Elsevier BV. - 0167-4730. ; 51:1, s. 35-46
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Tidskriftsartikel (refereegranskat)abstract
- Numerous methodologies for estimating the reliability of fibre-reinforced plastics have been published in the past few decades. Several of these methodologies use different mechanical and probabilistic models, each one based on a number of assumptions and approximations. The objective of this study is to assess common assumptions and approximations made on mechanical and probabilistic models used in reliability analyses of fibre-reinforced plastic laminates. The assessment consists of two parts: a theoretical overview of the models and their justification, and an investigation of the quantitative influence of the models on the reliability estimates of a group of fibre-reinforced cross-ply laminates. The reliability estimates are calculated through Monte Carlo simulations using different mechanical and probabilistic models. This study concludes that both mechanical and probabilistic models can significantly influence the reliability estimations. For the mechanical models, the factor with the greatest influence is the definition and modelling of matrix cracking. While, for the probabilistic models, the choice of probability distribution for modelling ply property variability has the greatest influence.
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| 14. |
- Stewart, Mark G., et al.
(författare)
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Assessment of risk reduction strategies for terrorist attacks on structures
- 2023
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Ingår i: Structural Safety. - 0167-4730. ; 104
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Tidskriftsartikel (refereegranskat)abstract
- Attacks on infrastructure have been a common feature of terrorism over many decades. The weapon of choice is often a Vehicle-Borne Improvised Explosive Device (VBIED) or a person-borne or other type of IED. The consequences of a successful attack in terms of casualties, physical damage, and other direct and indirect costs including societal costs can be catastrophic. Protectives and other risk reduction measures can ameliorate the threat likelihood, vulnerability or consequences. There is a need for a rational approach to deciding how best to protect infrastructure, and what not to protect. Hence, this paper describes a probabilistic risk assessment for the protection of infrastructure from explosive attacks. This includes a description of terrorist threats and hazards, vulnerability assessment including progressive or disproportionate collapse, and consequences assessment. Illustrative examples of the decision analysis consider the optimal risk reduction and design strategies for bridges and the progressive collapse of buildings.
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| 15. |
- Thöns, Sebastian
(författare)
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On the derivation of the delta formulation for decision value
- 2024
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Ingår i: Structural Safety. - 0167-4730. ; 109
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Tidskriftsartikel (refereegranskat)abstract
- This paper contains decision analytical approaches, conditions and models for the quantification of decision values for built environment systems. Specifically, (1) delta formulations of objective functions for decision value quantification are introduced, (2) conditions for decision value are identified and (3) action value analysis formulations are further developed. The delta objective functions are formulated with differences in utility, cost, and probabilities for consistent decision identification by expected utility and value. The delta formulations facilitate the direct calculation of action and information values and the explication of conditions for a positive decision value. Action value objective functions are derived in delta formulation for the action types of utility and system state actions and with action implementation states and action uncertainty models. The delta formulations are exemplified for predicted information and predicted actions values. The paper closes with a synthesis and discussion of decision values and with findings encompassing a computational effort reduction and the identification of predicted information value mechanisms.
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