PSI - Issue 55

Dulce Franco Henriques et al. / Procedia Structural Integrity 55 (2024) 214–221 Henriques et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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Carvalho (1996) for calculating the reference transverse tension strength from values obtained in wood with moisture contents other than 12% (Equation 3). 12 = [1+ 3 ( − 12)] (3) Where: - k 3 is generally considered equal to 0.015 - σ t12 – reference transverse tensile strength for MC = 12% - σ tH – transverse tensile strength for H% - H – MC different from 12% Table 1 shows data obtained from in situ tests (moisture content and penetration resistance) and from laboratorial tests. The real density data was obtained from the wood core that was extracted and compared with the values estimated by the penetration resistance test. There is an excellent agreement between these values, with a discrepancy of less than 5%. Both sets of data indicate a low wood density. Based on this, the conclusion can be drawn that the penetration resistance test is a reliable method for estimating wood density, as it closely aligns with the actual density data obtained from the extracted wood core. Furthermore, both methods consistently indicate that the wood in question has a low density.

Table 1. Data from in situ and laboratorial tests

Moisture content (H%)

Penetration average corrected for H% (mm)

Density (kg/m 3 )

Penetration test (mm)

Estimated average compressive strength (MPa)

Estimated (penetration)

Real (core)

Std (mm)

Differential (%)

each test average each test average

Beam V1

8.7 9.5 8.8 9.1 9.0

19.5 18.5 20.5 21.5 23.5

27.2

405

387

9.0

20.7

1.9

19.8

4.8

3.2. Visual Strength grading Beam V1 has two factors described in the standard BS 4978:2007 as leading be excluded from the grades: insect damage and wane that reduces the full edge and face dimensions to less than 2/3 of the dimensions of the piece. However, since it is considered that the beam will be reduced to its residual cross-section for rehabilitation purposes, these two hindering factors no longer exist or become irrelevant. In the case of elements in service, it is not important to know whether the element shows signs of biological degradation. What is important is to quantify the extent of this degradation to estimate the loss of the member's resistance capacity (Machado et al. 2009). In order to strength grading the structural member, two critical sections SC1 and SC2 were analysed. These critical sections were defined according to Cruz et al (2015): both are located near the mid-span, simultaneously combining the highest stress state with the occurrence of combinations of knots and double wane. The beam was graded according to significant parameters for wood in service (Machado et al, 2009): knots, slope of grain and rate of growth, in accordance with BS 4978:2007, since it is Scots pine. The authors decided to also consider fissures due to their extent. Wane and biological degradation will be removed by considering only the effective cross-section of the member as relevant. This standard establishes parameters and measurement criteria that can lead to two grades: General Structural (GS) or Special Structural (SS). Table 2 shows the values and grade obtained. 3.3. Conclusion of the case study The conclusion is that the beam can be classified as class GS, which for Scots Pine corresponds to strength class C14, according to NP 1912:2013. This class allows for an average density of 350 kg/m 3 , according to EN 338:2016. The tests carried out showed that the beam has a density of around 400 kg/m 3 , representing safety in relation to the class. Regarding compressive strength, this class allows structural members to have a characteristic value of 16 MPa or higher, according to EN 338:2016. The average value estimated for the beam is 27.2 MPa, which also represents