This paper is a concise explanation of the normative background to strength grading in Europe, addressing important aspects that are commonly misunderstood by structural engineers and timber researchers. It also highlights changes that are being made to the standards to: incorporate requirements of the Construction Products Regulations; add improvements to the system to accommodate the latest knowledge and technology; and widen the application of the standards.Where designs need to be optimised, there is an opportunity to use the system more intelligently, in combination with the latest technology, to better fit design values to the true properties of the timber resource. This can bring a design enhancement equivalent to effort improving other aspects of the structure, such as connectors and reinforcement. Parallel to this, researchers working on other aspects of structural improvement need to understand what grades really mean in respect of the properties of the timber, in order to correctly analyse the results of testing. It is also useful to know how techniques used in grading can assist with material properties characterisation for research.The amount of destructive testing involved in establishing machine grading settings and visual grading assignments presents a barrier to greater use of local timber, and diversification of commercial species, so it is important that any researcher assessing the properties of such species should consider, from the outset, doing the research in a way that can contribute to a grading dataset at a later date. This paper provides an overview of what is required for this.

International audienc

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The paper introduces the principal findings of a testing programme carried out to assess the performance of a newly developed blind-bolt. The blind-bolt, an evolution of the Lindapter-Hollobolt, is intended for use when making moment-resisting connections to Rectangular Hollow Sections. To date, the testing programme has concentrated on ascertaining the tensile strength and axial stiffness of the bolt, with tests subjecting the blind-bolt to a predominantly tensile load in a representation of the tensile region of such a connection. The results of the initial tests have shown the new blind-bolt to possess sufficient stiffness to classify the connection as moment-resisting but a lower tensile strength than standard bolts. However, the addition of a concrete infill to the tube in later tests has resulted in a tensile strength equivalent to standard bolts together with axial stiffness sufficient to classify the connection as rigid.

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Results of the recently approved machine control grading settings for Douglas fir in the Republic of Ireland and the UK have shown that the species can be graded to C18, and higher strength classes, and while there is a relatively high proportion of low strength timber, useful yields of grades up to C35 can be achieved. Large differences were found between subsamples, but it is believed that this is not a geographical difference between Ireland and the UK, but a feature of the representative sampling, and consequence of much more localised variation in timber quality.

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