Towards a performance-based standard for structural timber bondlines

摘要

Current standards for structural wood adhesives prescribe their chemical type,limiting the choice to phenolics for outdoor exposure and amino-plastics for indoor and protected outdoor exposures.There is growing dissatisfaction with this approach and the disincentive it imposes on adhesive manufacturers to develop new wood adhesives,especially the ones with different chemistries.The failure of phenolics to bond high density hardwoods,wastage and waste disposal problems associated with their use and the increasing application of adhesive-bonding technology in engineered timber products highlight the need for a performance-based adhesive-bond standard unshackled by chemical prescriptions.Although a number of issues need to be addressed in developing the standard,including those of strength,creep resistance,resistance to high (fire)and low (freezing)temperatures,moisture resistance and gap filling ability,the most intractable issue concerns bond durability.Load carrying structural components are expected to support loads over periods of 50 years or more without serious degradation in their load carrying capacity.The central issue is how to predict long term durability on the basis of relatively short duration tests.This paper concerns itself with the development of an international (ISO),performance-based standard for the performance of adhesive bonds.