Abstract
The management and preservation of structures in our built environment are central and challenging tasks for practicing engineers. Within the CEN member states (European Committee for Standardization), the so-called Eurocodes form the basis of the design and verification of the load-bearing capacity of structures. Current Eurocodes do not contain special recommendations for existing structures, meaning that the principles for new structures are applied. This can lead to an incorrect estimation of the load-bearing capacity within the semi-probabilistic safety concept. A central task within the investigation and evaluation of existing structures is the strength grading of the material in situ using non-/semi-destructive technical devices. Studies show the potential of the ultrasonic time-of-flight measurement in combination with visual evaluation for an improved grading. The information on the material from an improved grading technique can be used to update the material parameters as a target variable using a measured reference variable. In this contribution, test data from a partner project (spruce, pine, and oak) are analyzed, applying the stochastic grading model of Pöhlmann and Rackwitz. It can be shown that different grading techniques influence the updated distribution function of the material strength within the grade. The results depend on the timber species. Perspectives to develop updated models dependent on the knowledge available are shown and discussed.
Highlights
The evaluation of the load-bearing capacity of structural members in existing buildings embraces numerous challenging aspects
To estimate the material strength of a structural member made from timber, the material is graded into strength classes of EN 338:2016-07 [4] applying national grading standards and the assignment criteria of EN 1912:2013-10 [5]
The application of grading rules that have been developed for new structures on elements in existing structures is difficult, as elements are Buildings 2020, 10, 30; doi:10.3390/buildings10020030
Summary
The evaluation of the load-bearing capacity of structural members in existing buildings embraces numerous challenging aspects. To estimate the material strength of a structural member made from timber, the material is graded into strength classes of EN 338:2016-07 [4] applying national grading standards and the assignment criteria of EN 1912:2013-10 [5]. This procedure results in a lower variability of the material properties within a class compared to the ungraded material. The variability of strength properties within a class depends on the quality of the grading procedure, see [6]. The application of grading rules that have been developed for new structures on elements in existing structures is difficult, as elements are Buildings 2020, 10, 30; doi:10.3390/buildings10020030 www.mdpi.com/journal/buildings
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