Evaluation of the Load-Bearing Capacity of Timber Members in Existing Structures Based on Information from a Qualified Investigation In Situ Within a Stepwise Procedure

Abstract

AbstractEnhanced knowledge from a qualified survey in situ can help to model the load-bearing behaviour of an existing structures more realistically by considering specific knowledge on material parameters and conditions. A semi-probabilistic evaluation format with partial safety factors is used in common practice. Standardised options to include specific information into the design concept have to be worked out. These are improved strength grading using non-/semi-destructive means and adjustments within the safety concept itself. However, for everyday practice two problems arise. It is often not possible to determine strength parameters but reference properties like Young’s modulus or density. Besides, an exhaustive determination of material parameters is cost-intensive and therefore often not possible for smaller projects. This contribution presents a procedure to include data gained in a qualified survey in situ into the design concept for the verification of load-bearing capacities of existing timber structures. The level of detail of the design format is increased stepwise considering the level of detail of the survey. These levels are named Knowledge Levels in accordance with the Science and Policy Report of the Joint Research Centre (JRC) from 2015. Knowledge Level 1 includes the evaluation based on current Eurocodes without adjustments. Knowledge Level 2 is divided into three sub-levels including adjustments of partial safety factors for target values derived for existing structures, an improved strength grading based on non-/semi-destructive technical means and the updated of the partial safety factor for the material strength based on measured reference properties. Knowledge Level 3 includes a probabilistic evaluation comparing the actual reliability of the current design situation with and without parameter update.KeywordsTimberExisting structuresEvaluation procedureSemi-probabilistic safety conceptPartial safety factors