Abstract

Variations in environmental conditions can affect the structural performance of timber components and constructions. Especially in case of historic masonry buildings, where timber elements can be found either in roof or floor structures, intrinsic defects (e.g., knots, cracks, degradation), as well as the surrounding environmental conditions (e.g., temperature and moisture) can play an important role in the assessment of the mechanical response of the elements. In this connection, non-destructive (ND) and minor-destructive (MD) procedures are used to investigate the onsite conditions of wood, which are commonly based on either tool penetration resistance or wave transmission devices. In the paper, the influence of moisture content (MC) measured with various devices on a series of both old and new timber elements was compared. The elements made of various wood species (mainly red fir, but also white fir, pine and larch) were subjected to laboratory ND and MD testing by three research groups. Results showed the low influence of the MC on MD tests (i.e., resistance drilling and pin penetration) in comparison to the ND (i.e., sonic/ultrasonic) ones. Correlation relationships are provided, which illustrate and approximatively quantify the effect of MC for the experimentally investigated conditions and test equipment.

Abstract

Resistance drilling devices are commonly used for the onsite inspection of wood and timber structural components in existing buildings. Although they provide a measure related to the density variation along a section of an element, results are used mainly qualitatively, due to several parameters that affect the computed values. In this paper, several new and old timber elements, taken from the dismantling of original roofs from a large existing historical building in northern Italy, are tested through a series of ND (non-destructive), SD (semi-destructive) and destructive testing procedures. Various wood species (spruce, fir, larch, oak, elm, pine) are taken into consideration. Among the applied testing methods (visual inspection, resistance drill, ultrasonic, needle penetration, radar, lab tests bending/compression), not all reported here, a focus on the resistance drill tests results is addressed, to evaluate the influence of consumption of the needle tip on the amplitude output. This was done by correlating the drillings to a reference sample on each test position to obtain data with an enhanced quantitative content. From the visual old timber elements grading, SD tests execution and successive element strength characterization through laboratory tests, it finally emerged the need for proper calibration of assessment methodologies through the application of a combined approach, in order to achieve more reliable results.