Predicting the density of structural timber members in service. The combine use of wood cores and drill resistance data

M J Morales-Condea,C Rodríguez-Liñán,J Saporiti-Machado

doi:10.3989/mc.2014.03113

Abstract

Drilling devices is used to get information about the cross-section properties and internal defects of structural members. Drill resistance is correlated with density which is often used to predict the mechanical properties of timber elements. However in situ a regression curve cannot be obtained and pre-existent curves provides unreliable predictions. The present paper proposes a procedure for in situ “calibration” of drill resistance data. The “calibration” is based on density values from wood cores taken in the close vicinity of drill holes. Two approaches were tested. One approach based on a regression curve built using wood cores density and drill resistance values obtained from a limited number of members. The other approach uses the information of one wood core to “calibrate” the drill resistance profile taken at the same member. Following this procedure a density prediction is obtained showing a low mean percentage error and a medium coefficient of determination.

Highlights

IN THE USE OF DRILL RESISTANCE FOR ASSESSING TIMBER ELEMENTS IN SITUDrill resistance measures the torque applied to the needle in order to maintain a constant penetration velocity into the wood piece
Wood cores are used for obtaining a direct reading of the density of the superficial layers of timber members
The group approach showed a high correlation (r2 = 0.73) between the resistographic measure and wood cores both measured over the same wood volume

Summary

Introduction

IN THE USE OF DRILL RESISTANCE FOR ASSESSING TIMBER ELEMENTS IN SITUDrill resistance measures the torque applied to the needle in order to maintain a constant penetration velocity into the wood piece. IN THE USE OF DRILL RESISTANCE FOR ASSESSING TIMBER ELEMENTS IN SITU. Density variations in the wood material will correspond to variations of the torque production and result in a resistance drill profile along the depth of the wood element. The available equipments produce a very small drill hole (diameter between 1.5 and 3 mm) in wood. This damage does not affect the structural behaviour of timber members. Drill resistance technique is generally used to: assess the presence and extension of biological deterioration, mainly decay [6]; to predict the density profile [2]; and, the strength of clear wood [7].

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