The use of a visual grading code of practice in the UK in the assessment of the mechanical properties of in situ structural timber elements

Bather, Michael J.; Ridley-Ellis, Dan J.

Abstract

The estimation of the mechanical properties of in situ timber elements is an essential part of the structural appraisal of many existing buildings and structures. Currently, in the UK, this appraisal
of load-bearing timber is generally carried out by a structural engineer based on a combination of engineering judgement and visual assessment; frequently making use of UK codes of practice for
visual strength grading (CP112, BS4978 or BS5765). Despite their frequent use in this manner, these visual grading codes were not written for this purpose and were never intended to be used in
this way. The intended use of the codes is the strength grading of consignments of timber elements prior to their use in the construction industry. It is therefore necessary to consider the validly of the methodology of using the visual grading codes for in situ strength assessment. As a case study, 143 structural sized specimens of Norway spruce (Picea abies), sourced from the UK, were visually
graded (using CP112) and then tested to destruction to obtain their mechanical properties. The results, when analysed, illustrate the weakness in prediction by visual grading. The key implication
of this is that structural engineers in the UK should be made aware of the basis and limitations of using visual grading codes in the assessment of individual in situ structural timber elements, so
that they do not overestimate the power of visual grading methods and the importance of visual grading indicators, but also do not unnecessarily under-evaluate the performance of timber in situ.

Citation

Bather, M. J., & Ridley-Ellis, D. J. (2019). The use of a visual grading code of practice in the UK in the assessment of the mechanical properties of in situ structural timber elements. In SHATiS 2019: 5th International Conference on Structural Health Assessment of Timber Structures (89-98)

• Conference Name: 5th International Conference on Structural Health Assessment of Timber Structures (SHATiS)
• Conference Location: Guimarães, Portugal
• Start Date: Sep 25, 2019
• End Date: Sep 27, 2019
• Acceptance Date: Sep 25, 2019
• Publication Date: Sep 25, 2019
• Deposit Date: Sep 11, 2021
• Publisher: Universidade do Minho
• Pages: 89-98
• Book Title: SHATiS 2019: 5th International Conference on Structural Health Assessment of Timber Structures
• Keywords: Timber grading, In situ assessment, Norway spruce
• Public URL: http://researchrepository.napier.ac.uk/Output/2801259