Journal

Quality and Performance of Structural Timber

Germund Johansson, Assoc. Prof., Division of Steel and Timber Structures, Chalmers University of Technology, Göteborg, Sweden I. Robert Kliger, Ph.D., Assoc. Prof., Division of Steel and Timber Structures, Chalmers University of Technology, Göteborg, Sweden Mikael Perstorper, Ph.D., Assoc. Prof., Division of Steel and Timber Structures,Chalmers University of Technology, Göteborg, Sweden

Building contractors are generally not satisfied with the quality of sawn timber, primarily because of its excessive distortion. The grading regulations and standards do not prevent poor quality timber to reach the end-user. In this paper, a systematic analysis of the end user’s expectations is presented and is illustrated using a product specification for floor joists. These set of requirements comprises of geometrical dimensions including tolerances, straightness values (for maximum twist, spring and bow), important mechanical properties (strength and stiffness utilization factors for common loading cases) and other general requirements. The proposed acceptance levels are based on interviews with contractors and derived from the requirements set for the floor. The current grading rules are more generous than our proposal. If timber is to hold its own as a building material, the forest and sawmill industry will have to produce products with properties which match the end user’s requirements. Timber has to leave the old bulk era and enter the new product era. This also means that a more product-oriented grading system is needed. The current strength-related grading systems are not enough. Buying rules/standards for each type of product are needed in order to make it possible for the timber seller to fulfil the buyers demands.

Issue 3 Volume 9

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