The article presents a contribution to the current debate on the probabilistic representation of the wind speed extremes for calibration of the partial safety factor covering wind action. The requirements for the probabilistic model are formulated. The Gumbel distribution is shown to represents best the 10-minutes mean wind velocity yearly maxima based on theoretical considerations and analyses of real data with different statistical techniques.Data from locations across a large geographical region indicate that the coefficient of variation of the distribution varies over the territory. A method is proposed for accounting this variation in order to calibrate a single partial safety factor for the whole territory. The distribution location is indirectly given in design standards through the georeferenced characteristic wind speed values. A solution for including the uncertainty affecting these values is suggested. The findings are implemented in an illustrative calibration exercise. The proposed methods and concepts might be applied to other environmental actions such as the snow loads.
A framework for calibrating the reliability elements in simplified semi-probabilistic design safety formats is presented. The objective of calibration is to minimize the increase of construction costs, compared to the non-simplified safety format, without reducing the level of structural safety. The framework is utilized for calibrating two simplified safety formats which aim at reducing the number of load combinations relevant in structural timber design. In fact, the load-duration effect makes the design of timber structures more demanding since a larger number of load combinations need to be considered compared with other construction materials.Keywords: simplified safety formats, code-calibration, timber, reliability, load-duration effect.
IntroductionCurrent standards for timber design, such as the Eurocode 5 [1], have reached a high level of sophistication, extensiveness, efficiency and completeness at a cost of increasing the number and complexity of design rules, principles and requirements. This is the result of a code-development process driven mainly by the need to extend the standards to new materials, solutions, technologies, calculation tools and mechanical models. The associated drawback is an increased, and sometimes unnecessary, complexity of structural design, particularly for common and simple structures. Therefore, code provisions should balance simplicity, economy, comprehensiveness, flexibility, innovation, and reality [2]. These properties are usually mutually
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