Evaluation of Timber Degradation Caused by Insects to Quantify the Mechanical Strength of Load-Bearing Elements

ABSTRACT

Timber elements within historic structures are often susceptible to biological decay caused by insects. The areas affected by insect attacks are typically not considered in the structural analysis, although they may still provide some strength. Hence, accurately assessing the extent and intensity of insect damage is crucial for determining the actual strength of timber members. The present work presents the results obtained on insect-damaged timber members that were evaluated based on the proportion of the surface area occupied by bore holes, a method that is readily applicable by skilled operators during on-site inspections. Resistance to penetration (by drilling) and standard mechanical tests were then carried out to measure density in addition to strength (compression, shear, bending) and modulus of elasticity in bending. The results evidenced moderate yet highly significant inverse correlations between degree of degradation and mechanical properties. In contrast, density showed no discernible correlation with the degree of decay, nor did penetration resistance. However, drilling resistance showed a robust correlation with density and mechanical characteristics. The coupling between visual assessment of decay and evaluation of resistance to penetration allowed accurate prediction of mechanical properties similar to healthy wood.

KEYWORDS:

• Biological damage
• drilling resistance
• historical timber structures
• in-situ survey
• mechanical properties
• visual assessment

Acknowledgments

The experimental material is from the Medici Estate of Cafaggiolo (Florence, Italy), kindly made available by Cafaggiolo srl of Barberino di Mugello (Florence, Italy).

The work was realized in the framework of DRESL project cod. 11430.27102016.099000169, financed in the program POR CREO FESR 2014-2020 by Toscana Region. The authors want to thank Massimo Mannucci of LegnoDOC srl, C-SIX srl and Impresa Aliberto Saccenti di Luca Saccenti sas as partners of the project.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Data supporting the findings of this study are available from the corresponding author upon a reasoned request.

Additional information

Funding

The work was supported by the Regione Toscana .