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Specification of the target reliability levels is one of the key issues of the assessment of existing structures. ISO 13822:2010 and ISO 2394:1998 indicate procedures for deriving the target reliability levels by optimisation of the total cost related to an assumed remaining working life of a structure. In the submitted study this approach is applied to estimate the target reliability levels of an existing structural member in conjunction with the human safety criteria. Obtained results are critically compared with the recommendations given in present standards. It appears that the requirement on the same target reliability levels for existing structures as for new structures is uneconomical. Further, the cost optimisation seems to yield rather low reliability levels and human safety criteria become commonly decisive for specification of the target reliabilities of existing structures.
Target reliability levels are derived by optimizing initial structural costs and considering three major types of potential consequences of structural failure: a) direct and indirect economic losses, b) societal consequences resulting from fatalities and injuries, and c) environmental impacts. The guidance on how to e stimate and combine these consequences is provided; societal consequences are expressed using the Life Quality Index (LQI) concept. The case study focused on a generic load-bearing member reveals that target reliability levels for structural design are commonly dominated by economic criteria.
The specification of target reliability levels and risk acceptance criteria is one of the key issues of design and reliability assessment of existing railway stru ctures including bridges, tunnels or secondary struc-ures like noise barriers. Target reliability levels obtained by optimisation of the total cost, related to a required working life of the structure, are critically compared with human safety criteria based on group risks, intended to avoid accidents with a large number of fatalitie s. Practical applications of the theoretical principles are demonstrated by the examples of a railway bridge, railway tunnel and road bridge over an important railway line. The examples illustrate on how probabilistic reliability analysis and risk optimisation can support decisions about alternative strategies to achieve the optimal designs complying with the requirements on human safety. The contribution reveals that target relia bility levels for civil engineering structures recommended in various normative documents are inconsistent in terms of the values and the criteria according to which the appropriate values are to be specified. The optimal target reliabilities from economic point of view primarily depend on failure consequences and costs of safety measures.
Specification of target reliability levels is one of the key issues of the assessment of existing structures. ISO 13822:2010 and ISO 2394:2015 indicate procedures for specification of target reliability levels by optimisation of the total cost related to an assumed remaining working life of a structure. These approaches are critically compared with human safety criteria, with target levels based on a marginal life-saving costs principle, and with recommendations of present standards. Optimal target reliability levels are then derived in the representative case study for an existing structural member. It appears that the requirement to reach the same target reliability levels for existing and new structures is uneconomical. Decisions made in the assessment can result in the acceptance of the actual state or in the upgrade of an existing structure. Two reliability levels are thus needed - the minimum level below which the structure is unreliable and should be upgraded, and the target level indicating an optimum upgrade strategy. It is recommended that these levels be established using economic optimisation and the marginal life-saving costs principle, as both the approaches take into account the costs of safety measures and the failure consequences.
Specification of the target reliability levels is one of the key issues of the assessment of existing systems. ISO 2394:2015 indicate procedures for specification of the target reliability levels by optimisation of the total cost related to an assumed remaining working life of a structural system. These approaches are critically compared with human safety criteria and with recommendations of present standards. It appears that the requirement on the same target reliability levels for existing civil engineering systems as for newly designed is uneconomical. Decisions in the assessment can result in the acceptance of the actual state or in upgrade of the existing structure, two reliability levels are thus needed - the minimum level below which the structure is unreliable and should be upgraded, and the target level indicating an optimum upgrade strategy. When reliability of a system or its key component is verified (as compared to design of a common component), the target reliability index should be increased by about 0.5.
This contribution shows how monitoring can be used to control reliability of a structure not complying with the requirements of Eurocodes. A general methodology to obtain cost-optimal decisions using limit state design, probabilistic reliability analysis and cost
estimates is utilised in a full-scale case study dealing with the roof of a stadium located in Northern Italy. The results demonstrate the potential of monitoring systems and probabilistic reliability analysis to support decisions regarding safety measures such as
snow removal, or temporary closure of the stadium.
A methodology for the evaluation of the annual probability of occurrence of post-elastic seismic damage in realistic structures is presented. The seismic damage hazard analysis (SDHA) is carried out here by coupling conventional seismic hazard analysis (SHA) for the site and the structural response to earthquakes of different intensities. The structural performance is statistically investigated by conducting appropriate non-linear dynamic analyses for a limited set of real ground-motion records that might potentially pose a threat to the structure at the site. The merging of these two approaches permits calculation of the seismic hazard faced by the structure in direct damage terms. The methodology is presented in this paper with the aid of a simple illustrative case study where the annual probability of damage and, eventually, failure of a power house steel structure is computed. This methodology can find practical applications in seismic retrofit of nuclear power plant structures and in the evaluation of seismic damage hazards in new structure designs.
The contribution demonstrates the benefits of Unmanned Aerial Vehicles (UAV)-based surveys for building damage evaluation and decisions on interventions after an earthquake. The case study focuses on the historic village of Castelluccio di Norcia (Italy), heavily damaged by the 2016 earthquake. By constructing a 3D model based on UAV flights, the damage levels are estimated for buildings in the village and an optimal set of intervention measures is proposed. For the decision analysis, a pre-posterior Bayesian technique is utilized. The efficiency of the UAV-based survey is highlighted through a cost-benefit analysis and by considering parameters such as the time constraints, the quality of obtained data and the risk of inspecting persons. The proposed method seems to be efficient in organizing rescuing activities, managing emergency measures and specifying interventions, following the occurrence of an accidental situation.
The scope of this contribution is to provide and analyse a rehabilitation concept for typical brick residential buildings in Nepal damaged after the spring 2015 earthquake of magnitude 7.8. Development workers of Engineers Without Borders Germany travelled the same year to the village of Lurpung, southeast of Kathmandu to inspect damages and recommended primary approaches for the earthquake-resistant reconstruction of residential buildings [1].
A detailed restructuring concept is developed herein based on the aforementioned recommended approaches and optimized in terms of time and cost based on information reflecting site conditions and experience. For this purpose, a horizontal timber bracing has been designed, which consists to a large extent of local existing materials. It is demonstrated that the strengthening can be applied in an area of high seismic activity and to simple quarry stone masonry buildings typical for Nepal.
In a first stage, a detailed FE-model was developed, focusing on a realistic load-bearing behaviour of a representative typical structure. Thereby it is ensured that the most accurate internal forces and stresses can be obtained from the FEM analyses for further verification and retrofitting. Following the modelling, the equivalent static horizontal forces as a result
of the relevant response spectrum are generated using the FE-software. Based on this procedure and with reference to Eurocode EN 1995 [2] for timber structures, the bracing system has been dimensioned for the maximum normal force resulting from the earthquake with a return period of 225 years corresponding to a peak ground acceleration of 0.35g. The considered earthquake reflects the regional seismicity described herein by a respective response spectrum with regard to the seismic provisions of Eurocode EN 1998 [3]. The reduced return period of 225 years compared to 475 years applied in design is selected in order to reflect a more reluctant safety target for existing structures [4]. The respective seismic hazard analysis is taken from Pradhan [5] and Chaulagain [6] and represents site specific conditions.
The improvement of the overall load-bearing behaviour influenced by the bracing, is subsequently checked by verifying the masonry walls using the Eurocode for masonry EN 1996 [7]. The material resistance parameters are taken from local studies and related testing outcomes [8]. The obtained structural analysis results show that wall shear capacity is utilized up to a ratio of 65% and the wall bending capacity is exceeded by 72%. However, when compared with the original building, it can be determined that the mutual floor displacements can be reduced by a factor of up to 4.3 due to the proposed bracing system. Consequently, further retrofitting measures are recommended for the masonry. In that respect lower reliability levels can be of interest since a “discount” in the safety requirements for existing structures, however by fulfilling acceptable human safety levels, is usually unavoidable due to economical constraints.
The contribution leads to the conclusion that by retaining the static replacement system in the form of a truss, but adapting the building materials used, the basic functionality of the xamined system can be provided. Although the FEM calculations have demonstrated satisfactory results further experimental campaigns are necessary to define the material properties of the considered typical building structures with respect to the analysed failure modes. The proposed approach supports efficient design of interventions in post-earthquake phases.
Planning and designing railway tunnels with an explicit reference to safety issues is becoming of utmost importance since the combination of high speed, mixed goods–passenger traffic and extreme length of the new tunnels under design or concept evaluation, have sensitively modified the inherent safety of the railway tunnel. Although the probability of occurrence of accidental events may still be considered rather low, the possible consequences of such events in long tunnels can be catastrophic, therefore raising the overall risk to levels that may be no more acceptable. The scope of this paper is to illustrate the state-of-practice related to risk analysis of long railway tunnels. First, ambitious tunnel projects are briefly reviewed. The applicable risk-analysis procedures are then described and discussed. The problem of risk appraisal is addressed and quantitative target safety levels are proposed. Safety systems for risk reduction are outlined.