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Highlights • Proposal of NDT for density estimation in existing structural timber pieces. • Different measurement criteria depending on location of readings were analysed. • Optimizing accuracy and cost. • 45 specimens from 18th century building were analysed. Abstract The density of 45 structural Salzmann pine timber pieces with nominal dimensions of 150 × 200 × 5000 mm3 from an existing 18th century structure was estimated using the following non-destructive methods: needle penetration resistance (NPR), screw withdrawal resistance (SWR) and drilling chips extraction (DCE). Non-destructive testing (NDT) measurements were correlated with actual and apparent density (considering a rectangular cross-section instead of the actual profile). Ten non-destructive measurements were taken in each specimen with each device. The best results were obtained with DCE and the poorest with NPR. The increase of the determination coefficient obtained by increasing the number of measurements did not show a great improvement from the fifth to the tenth measurement: r2 = 0.12–0.65 for one reading, 0.35–0.77 for five readings and 0.42–0.76 for ten readings, depending on the device. Because density varies along pieces, three accumulated measurement sequences along them were analyzed to correlate better with the minimum number of readings: Linear (LM), End to Centre (ECM) and Centre to End (CEM) methods. CEM was the most effective sequence, giving higher r2 than the others. In practical work involving the in-situ estimation of density it is recommended that a minimum of 3 or 4 measurements using CEM be performed. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to define the reference conditions and to propose modification factors to standardize the variables recorded by different nondestructive techniques. This practice will make it possible to generate consistent practical data while developing a procedure for the standardization of timber structure assessment. The nondestructive variables analyzed are: time of flight, natural frequency, pullout resistance, penetration depth and drill resistance. The factors which affect these variables are: moisture content, temperature, size/length and positioning of sensors and angle to the grain. Reference conditions are defined and equations and modifications factors are proposed to help in the evaluation of existing timber structures and decision making. [ABSTRACT FROM AUTHOR]

• Strength capacity of an 18th century timber structure using NDT verified with load tests. • Structural behavior of the floor slab considering the transverse stiffness of the system. • Strength estimation (bending, compression and shear) through their relationship with stiffness. • Verification of structural safety in accordance with Eurocode 5 Timber structures. The timber structural members of a seven-story building from the end of the 18th century were evaluated following a procedure based on previous research works. The structure consisted of timber-framed brick walls and heavy timber floors with mortar filling. Non-destructive measurements were taken in 13 sampling areas of the floors and framed walls. Detailed measurements of at least 3 pieces in each sample were taken (stress wave Time-of-Flight and probing tests). Mean density and modulus of elasticity values and characteristic values of bending and compression strength were estimated. On-site load tests were carried out on three floor slabs to deduce their actual bending stiffness and compare it with estimation by NDT. They behaved more rigidly than expected, which is explained by floor screed stiffness, the transverse stiffness effect and possible semi-rigid connection behaviour at the supports. Structural verification determined the required strength of the critical members to compare this with the estimated strengths, showing a correct safety level. [ABSTRACT FROM AUTHOR]

• Systematized method for the evaluation of bending timber structures: wave velocity, density and VSG. • Comparison between ungraded and graded timber through MOR and MOE relationships. • It was verified that density estimation with the WOODEX was similar to actual density. • A factor is proposed for the relationship between dynamic and static MOE based on previous experiences in pieces with similar characteristics. • MOR prediction models can be improved by adding to the MOE, knotty and slope of grain. The modulus of elasticity and bending strength of 45 structural Salzmann pine timber pieces with nominal dimensions of 150x200x5400 mm3 from an existing 18th century structure were estimated by semi-destructive density estimation probing method (drilling chips extraction) and acoustic wave velocity (stress and ultrasound wave). Bending strength, modulus of elasticity and density were obtained according to the EN 408 European standard, and visual grading singularities were recorded. Visual grading methods are highly ineffective for existing timber structures. Sample mechanical properties show a typical profile of material from existing structures, and this was compared with the results of similar works. MOE and MOR predictive models were proposed with determination coefficients r2 of 66–68% and 51–52%, respectively, using dynamic MOE, relative edge knot diameter and slope of grain as independent variables. MOR prediction improved when these grading parameters were included. [ABSTRACT FROM AUTHOR]