Partner und Internationale Organisationen
(Englisch)
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A, B, CZ, DK, F, D, IRL, I, NL, N, PL, RO, SI, E, S, CH, GB
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Abstract
(Englisch)
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Chapter 3 - Uncertainty If all information is known about a structure, including all of the material properties in the structure, all of the loads to which the structure is and will be subjected, and how the structure does and will behave when subjected to these loads, it is possible for an engineer to say whether or not a structure will survive a certain period of time. Since it is not possible to know each of these exactly, engineers must make conservative approximations and estimations, which allow structures to be designed and assessed. With each approximation and estimation there is associated uncertainty. The sources of these uncertainties are often classified as either 1) natural - uncertainties due to the unpredictability of loads such as wind, earthquake, snow, etc…, and the differences in mechanical behaviour of the materials in a structure; or 2) human - uncertainties due to intended and unintended departures from the optimal design, during the design phase, such as approximations and calculation errors, and during the construction phase, such as the use of non-specified materials and changes without analysis. In the assessment of existing structures, engineers do not have to work with the same uncertainties that existed during the design phase. The structure now exists. The loads to which the structure is subjected can be measured to give a more accurate portrayal of the extreme loads to which the structure is subjected and to which it will be subjected in the future. The material properties in a structure can be measured, which often has the effect of removing the conservative bias that the engineer had at the time of design. The overall structure can be tested to determine more accurately the structural behaviour and ensure that appropriate models of structural response are being used. The uncertainties in the evaluation of structures are due to inherent variability, and imperfect modelling and estimation error. These uncertainties can be incorporated into the assessment processes using probabilistic methods. Chapter 5 - Material properties In order to assess highway structures it is necessary to accurately model the resistance of the structural elements in these structures. This requires knowledge of the material properties in the structural elements, such as strength and stiffness, as well as the structural dimensions and how the various materials within the elements act together. It is also necessary to understand the influences on the material properties and structural dimensions, of time (i.e. the size and strength changes due to deterioration mechanisms such as fatigue and corrosion), fabrication methods and quality control measures (such as construction and in-service inspections). The correlation effects between different properties and between different locations within the elements and structures must also be known. This chapter addresses material properties in a general way that is applicable to the assessment of all materials that are used in highway structures, and gives some more specific details on the considerations required when modelling concrete and steel reinforcement. Section 5.2 explains variations in material properties and how they are modelled. Section 5.3 discusses the consideration of initial compliance controls. Section 5.4 and 5.5 discuss, as examples, aspects to be considered when modelling the concrete and steel reinforcement that comprise concrete elements, respectively. The reader is referred to Appendix B for a more detailed look at the mathematical and probabilistic models proposed for various material properties by various researchers.
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