Most of the old and heritage structures are constructed using timber members. While assessing the structural stability of these timber framed structures, it becomes necessary to assess the condition of timber members and especially joints. Wood deterioration is one of the most common damage mechanisms in timber structures and often inflicts damage internally. Timber’s mechanical properties are affected by natural characteristics (orientation of loading regarding fibre orientation, density, knots and slope of grain) and by service conditions (moisture content, load duration), which turns extremely difficult the strength assessment of timber in service (residual strength). The timber is deteriorated mainly due to wet rotting and by termites making it either soft or creating hollow pockets. several types of fungi attack wood. The hyphae of these fungi secrete enzymes that depolymerize the chemical components of wood, thereby reducing the density, strength, and hardness of a member. This results in a significant reduction in load-carrying capacity, which in turn may result in the member’s failure. The Micro- Drill resistance tests can be used to detects such defects in the timber members
Principle & Procedure
Resistance (recording) drilling with thin needles is used to deter¬mine the condition of structural timber and joints by measuring density profiles of wood, in order to detect decay, insect damage, cracks, invisible beams and hidden parts
A small needle of 1.5 to 5.0 mm dia penetrates into a wooden structure at a constant speed and the drilling resistance is measured.
