In routine engineering practice, the risks associated with safety considerations addressed when designing new or assessing existing structures are not quantified and the corresponding acceptance criteria may diverge widely. Although the use of explicit risk analysis methods to quantify structural safety would therefore deliver significant benefits, the implementation of such methods is hindered by a series of technical and administrative obstacles. The present study explores methods and tools for the practical application of explicit risk analysis methods. Structure-related risks to persons are established on the grounds of the probability of structural failure and its consequences in terms of loss of human life. The procedure adopted is applied to a representative set of building structures. Acceptance criteria for risks to persons associated with such structures are deduced from the findings. These criteria provide a rational basis for decision-making in structural engineering. They may be used in explicit risk analysis or as a basis for the consistent calibration of simplified models for determining partial factors in the design of new or assessment of existing structures.
In the recent past, the NOx removal efficiency of photocatalytic materials has been subject of many studies with promising results. However, many of these studies involve laboratory tests carried out under standardized climatic exposure conditions, often not representative of the real world environment. With the aim to bridge this gap, selected photocatalytic materials have been applied to different substrates in outdoor demonstrator platforms at pilot scale as part of the project LIFE-PHOTOSCALING. The paper presents the results of in situ measurements of NOx removal efficiency of the materials, performed during 17 months. Statistical models accounting for the influence of exposure time and relevant environmental variables are derived. They suggest that photocatalytic emulsions on the tested asphalt experience a significant loss of activity over time irrespective of climatic conditions. The efficiency of photocatalytic slurries on asphalt and of concrete tiles, with the photocatalyst applied on surface or in bulk, mainly depends on substrate humidity.
Like other competitive bridge erection techniques, incremental launching is a highly vulnerable process that entails considerable risks to persons. In steel and composite bridges, in particular, patch loading and other mechanisms that induce instability must be avoided. Considerable uncertainties are associated with both resistances and support reactions during launch operations due to the broad range of factors involved. Nonlinear finite element (FE) analysis is very useful for the explicit verification of both local and overall system stability during steel structure launching. Monitoring, in turn, may be a very powerful tool for reducing the risks associated with such operations. Further research is needed both to establish safety levels for temporary structures and on-site activities and to develop a suitable design format for nonlinear FE analysis. However, in everyday practice, engineers and builders must deal with much more basic problems, often related to the interaction between the structure under construction and the ancillary resources used, as exemplified in the case study described in this contribution. The lessons learnt from such incidents are extremely useful for improving the strategies presently in place to reduce construction-related risks.
The relatively high failure rates, with important consequences in many cases, suggest that the implicitly acceptable risk levels corresponding to temporary civil engineering structures and activities might exceed the bounds of normally acceptable levels associated with different societal activities. Among other reasons, this may be attributed to the lack of a rational approach for the assessment of risks associated with the different technologies supporting these activities in general, and for structures in particular. There is a need for establishing appropriate target reliability levels for structures under temporary use taking into account specific circumstances such as reduced risk exposure times. This issue is being addressed in the present paper. Acceptance criteria for building structure related-risks to persons obtained in prior studies are adapted to the special circumstances of non-permanent risk exposure. Thereby, the general principle followed is to maintain the same risk levels per time unit as for permanently occupied buildings. The adaptation is based on the statistical annual fatality rate, a life safety risk metric which allows for a consistent comparison of risks across different societal activities and technologies. It is shown that the target reliability indices taking account of the temporary use of buildings might be significantly higher than the values suggested for permanently used structures. 200 CHARACTER SUMMARY FOR SOCIAL MEDIA The inference of time dependent target reliabilities for structures under temporary use is addressed. As a general principle, the same risk levels per time unit as for load bearing systems of permanently occupied buildings are maintained.
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