Estimating Mechanical Properties of Wood in Existing Structures—Selected Aspects
Abstract
:1. Introduction
2. Selected Methods for Estimation Wood Structural Properties
2.1. Selected Standard Procedures and Tests
2.2. Mechanical Properties Assessment Based on Visual Grading
The Classification Basis | KW (Choice Class) | KS (Middle Quality Class) | KG (Lower Quality Class) | |||
---|---|---|---|---|---|---|
Variant 1 | Variant 2 | Variant 1 | Variant 2 | |||
Knots, regardless of quality, expressed as a knotting index USM | ≤1/4 | ≤1/4 | ≤1/2 | ≤1/2 | >1/2 | |
Over the entire cross-section of timber USC | ≤1/4 | ≤1/3 | ≤1/4 | ≤1/2 | ≤1/3 | |
Slope of grain (diagonal grain path) | ≤7% (1:14) | ≤10% (1:10) | ≤16% (1:6) | |||
Cracks, resin pockets, bark pockets and catfaces | Deep, not crossing to the face, sides and opposite plane (not including defects less than 300 mm in length) | Permissible, length up to ¼ of the piece length and not longer than 600 mm | Permissible, length up to ¼ of the piece length and not longer than 600 mm | Permissible, length up to ¼ of the piece length and not longer than 900 mm | ||
Frontal non-crossing, crossing and circular | Depth up to 1/3 of the piece thickness | Depth up to 1/2 of the piece thickness | Depth up to 2/3 of the piece thickness | |||
Decay | Impermissible | Impermissible | Impermissible | |||
Insect damage | Impermissible | Impermissible | Impermissible | |||
Sapstain | Permissible | Permissible | Permissible | |||
Reaction wood (compression wood) | Permissible up to 1/5 of the girth | Permissible up to 2/5 of the girth | Permissible up to 3/5 of the girth | |||
Growth ring index | ≤4 mm | ≤6 mm | ≤10 mm | |||
Minimum density of timber at a moisture content of 20% | ≥450 kg/m3 | ≥420 kg/m3 | ≥400 kg/m3 | |||
Wane is permitted along the entire length of two edges of one plane or on side, occupying a total of | Up to ¼ thickness and ¼ width of timber piece | Up to ¼ thickness and ¼ width of timber piece | (a) at a distance of up to 300 mm from faces up to 1/3 of the thickness and 1/3 of the piece width (b) at a distance of more than 300 mm from faces up to 1/2 of the thickness and 1/3 of the piece width | |||
Bow-longitudinal curvature of planes | ≤10 mm | ≤10 mm | ≤20 mm | |||
Spring-longitudinal curvature of the sides | ≤8 mm | ≤8 mm | ≤12 mm | |||
Twist in relation up to width | ≤1 mm/25 mm | ≤1 mm/25 mm | ≤2 mm/25 mm | |||
Cup-cross curvature to width | ≤1 mm/25 mm | ≤1 mm/25 mm | ≤2 mm/25 mm | |||
Cracks, kerf waviness | Permissible within the thickness and width deviations specified for basic dimensions | |||||
Parallelism of planes and sides | Planes should be parallel to each other; sides of edged timber should be perpendicular to planes; deviations from parallelism should be within the limits of acceptable thickness and width deviations specified for the basic dimensions | |||||
Non-perpendicularity of faces | Faces should be perpendicular to planes and sides; deviations from perpendicularity should be within the permissible deviations in timber length |
Tree Species | Thickness | KW (Choice Class) | KS (Middle Quality Class) | KG (Lower Quality Class) |
---|---|---|---|---|
Scots pine (Pinus sylvestris) | ≥22 mm | C35 | C24 | C20 |
European spruce (Picea abies) | C30 | C24 | C18 | |
European silver fir (Abies alba) | C22 | C18 | C14 | |
European larch (Larix decidua) | C35 | C30 | C24 |
2.3. Mechanical Properties Assessment Based on the Determination of the Dynamic Modulus of Elasticity
Wood Species | Vibration Method | Acoustic Method |
---|---|---|
Scots pine (Pinus sylvestris) | ||
Radiata Pine (Pinus radiata) |
2.4. Mechanical Properties Assessment Based on the Resistance Drilling Method
2.5. Mechanical Properties Assessment Based on Small Clear Wood Specimens Tests
Wood Property | Coefficient of Variation V [%] | ||
---|---|---|---|
ISO 3129 [59] | Krzysik [60] | Wood Handb. [61] | |
Number of growth rings in 1 cm | 37 | - | - |
Percentage of late wood | 28 | 28 | - |
Density | 10 | 10 | 10 |
Equilibrium moisture content | 5 | - | - |
Coefficient of shrinkage: linear | 28 | 28 | - |
Coefficient of shrinkage: volumetric | 16 | 16 | - |
Ultimate compressive strength parallel to grain | 13 | 13 | 18 |
Ultimate strength in static bending | 15 | 15 | 16 |
Ultimate shearing strength parallel to grain | 20 | 19 | 14 |
Modulus of elasticity in static bending | 20 | 20 | 22 |
Proportional limit (conventional ultimate strength) in compression perpendicular to grain | 20 | 30 | 28 |
Ultimate tensile strength parallel to grain | 20 | 20 | 25 |
Ultimate tensile strength perpendicular to grain | 20 | - | - |
Impact strength in bending | 32 | 32 | 25 |
Hardness | 17 | 17 | 20 |
3. Materials and Methods
4. Results
4.1. Results of Destructive Testing of Technical Scale Beams and Density Determination
4.2. Results of Tests with Acoustic Method
4.3. Results of Test with Drilling Resistance Method
4.4. Results of Tests of Small Clear Specimens and Their Adjustment to Structural Size Beams
Beam A01 | Beam A02 | Beam A03 | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Group 1 | Group 2 | Group 1 | Group 2 | Group 1 | Group 2 | |||||||
MOR | MOE | MOR | MOE | MOR | MOE | MOR | MOE | MOR | MOE | MOR | MOE | |
Mean [MPa] | 96 | 11,700 | 103 | 13,800 | 96 | 11,700 | 103 | 13,800 | 96 | 11,700 | 103 | 13,800 |
5% exclusion value (MPa) | 80 | 9800 | 66 | 9400 | 80 | 9800 | 66 | 9400 | 80 | 9800 | 66 | 9400 |
Special factor kp 1 [-] | 0.68 | - | 0.78 | - | 0.68 | - | 0.78 | - | 0.68 | - | 0.78 | - |
Factor kd 2 [-] | 0.60 | 1.0 | 0.60 | 1.0 | 0.53 | 0.90 | 0.53 | 0.90 | 0.75 | 1.00 | 0.75 | 1.00 |
5% exclusion value [MPa] “Characteristic" | 33 | - | 31 | - | 29 | - | 27 | - | 41 | - | 39 | - |
[MPa] “Mean” | 39 | 11,700 | 48 | 13,800 | 35 | 10500 | 43 | 12,400 | 49 | 11,700 | 60 | 13,800 |
5. Discussion
6. Conclusions
- In the conducted research, very good correlations were obtained between MOEstat from the acoustic method and MOE from beams on the technical scale. Nevertheless, the difference in the value of the modulus determined by the acoustic method may be high enough to result in an incorrect assignment of wood class.
- In the drilling resistance test, statistically significant correlations were observed between the density, MOR and MOE as predictors and FF or RM as the response (R2 = 0.49–0.62). However, it is considered that resistance drilling should be used for qualitative rather than quantitative evaluation of timber.
- In the conducted study, the MOE values determined in accordance with the ASTM standard, based on the results for small clear specimens, correspond very well with the actual values from the technical scale element tests.
- The failure of the technical scale beams in the bending tests was observed in the areas of occurrence of defects considered by ASTM D245 [44] to be critical for load-bearing capacity.
- It is recommended to use different methods in parallel, as no single method is sufficiently reliable.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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MOR | MOE | |
---|---|---|
Number of samples | 30 | 30 |
Coefficient of variation according to ISO 3129 | 15% | 20% |
Confidence level | 0.95 | 0.95 |
Estimated test accuracy rate | 5.37% | 7.16% |
Beam | MOR | MOE | Density [kg/m3] | ||||||
---|---|---|---|---|---|---|---|---|---|
Value [MPa] | Mean [MPa] | Standard Deviation [MPa] | Variation Coefficient ν [%] | Value [GPa] | Mean [GPa] | Standard Deviation [GPa] | Variation Coefficient ν [%] | ||
A01 | 37.46 | 38.39 | 6.23 | 16.23 | 11.62 | 11.36 | 0.37 | 3.23 | 497 |
A02 | 31.27 | 10.85 | 484 | ||||||
A03 | 46.45 | 11.63 | 496 |
Beam | Direction Relative to Grain | Velocity [m/s] | MOEdyn [GPa] | MOEstat 1 [GPa] | |||
---|---|---|---|---|---|---|---|
Fakkop MS | Sylvatest Trio | Fakkop MS | Sylvatest Trio | Fakkop MS | Sylvatest Trio | ||
A01 | parallel | 5292 | 5134 | 13.95 2Δ = 20.1% | 13.10 Δ = 12.7% | 11.11 Δ = 4.4% | 10.47 Δ = 9.9% |
perpendicular | 1689 | 1617 | 1.42 | 1.31 | 1.65 | 1.57 | |
A02 | parallel | 5262 | 5155 | 13.41 Δ = 23.6% | 12.87 Δ = 18.6% | 10.70 Δ = 1.4% | 10.29 Δ = 5.1% |
perpendicular | 1742 | 1559 | 1.47 | 1.18 | 1.69 | 1.47 | |
A03 | parallel | 5090 | 5038 | 12.86 Δ = 10.6% | 12.59 Δ = 8.3% | 10.29 Δ = 11.6% | 10.08 Δ = 13.3% |
perpendicular | 1668 | 1573 | 1.38 | 1.23 | 1.62 | 1.51 |
Beam | Number of Measurements | Resistance Measure RM [%] | |||
---|---|---|---|---|---|
Mean | Range | Standard Deviation | Coefficient of Variation | ||
A01 | 40 | 21.86 | 17.34–24.93 | 1.96 | 8.99 |
A02 | 40 | 18.84 | 17.33–20.67 | 0.95 | 5.04 |
A03 | 40 | 22.66 | 22.66–21.40 | 0.99 | 4.38 |
Summary | 120 | 21.12 | 17.33–24.93 | 2.15 | 10.17 |
Beam | Number of Measurements | Feed Force FF [%] | |||
---|---|---|---|---|---|
Mean | Range | Standard Deviation | Coefficient of Variation | ||
A01 | 40 | 28.76 | 24.56–33.68 | 2.41 | 8.39 |
A02 | 40 | 25.11 | 23.57–26.22 | 0.76 | 3.02 |
A03 | 40 | 30.28 | 28.49–31.90 | 0.75 | 2.48 |
Summary | 120 | 28.05 | 23.57–33.68 | 2.65 | 9.44 |
Beam | Variable | Estimate | Standard Error | p-Value |
---|---|---|---|---|
A01 | Intercept | 7.79 | 2.73 | .007 |
RM | 0.96 | 0.12 | <.001 | |
A02 | Intercept | 14.78 | 1.78 | <.001 |
RM | 0.55 | 0.09 | <.001 | |
A03 | Intercept | 17.19 | 1.80 | <.001 |
RM | 0.58 | 0.08 | <.001 |
Variable | Estimate | Standard Error | p-Value |
---|---|---|---|
Intercept | 7.79 | 1.76 | <.001 |
RM | 0.96 | 0.08 | <.001 |
Beam A02 vs. A01 | 6.99 | 3.58 | .053 |
Beam A03 vs. A01 | 9.40 | 4.00 | .021 |
RM: beam A02 vs. A01 | −0.41 | 0.18 | .027 |
RM: beam A03 vs. A01 | −0.38 | 0.18 | .034 |
Feed Force/Resistance Measure | Variable | Estimate | Standard Error | p-Value |
---|---|---|---|---|
FF | Intercept | −148.28 | 13.79 | <.001 |
Density | 0.36 | 0.03 | <.001 | |
RM | Intercept | −117.11 | 11.68 | <.001 |
Density | 0.28 | 0.02 | <.001 |
Feed Force/Resistance Measure | Variable | Estimate | Standard Error | p-Value |
---|---|---|---|---|
FF | Intercept | 15.47 | 0.96 | <.001 |
MOR | 0.33 | 0.02 | <.001 | |
RM | Intercept | 11.90 | 0.88 | <.001 |
MOR | 0.24 | 0.02 | <.001 |
Feed Force/Resistance Measure | Variable | Estimate | Standard Error | p-Value |
---|---|---|---|---|
FF | Intercept | −36.78 | 4.64 | <.001 |
MOE | 5.70 | 0.41 | <.001 | |
RM | Intercept | −29.19 | 4.01 | <.001 |
MOE | 4.43 | 0.35 | <.001 |
Group 1 | Group 2 | |||
---|---|---|---|---|
MOR | MOE | MOR | MOE | |
Number of specimens | 30 pieces | 30 pieces | ||
Mean value | 96 MPa | 11.7 GPa | 103 MPa | 13.8 GPa |
Standard deviation | 9.3 MPa | 1.11 GPa | 21.2 MPa | 2.57 GPa |
Coefficient of variation | 9.6% | 9.5% | 20.2% | 18.3% |
Confidence interval for the mean (0.95) | 92.7–99.3 MPa | 11.43–12.23 GPa | 95.1–110.3 MPa | 12.88–14.72 GPa |
5% exclusion limit | 80 MPa | 9.8 GPa | 66 MPa | 9.4 GPa |
Group | Variable | Estimate | Standard Error | p-Value |
---|---|---|---|---|
Group 1 | Intercept | 19.99 | 11.52 | 0.094 |
MOE | 6.52 | 0.98 | <0.001 | |
Group 2 | Intercept | 8.08 | 12.07 | 0.509 |
MOE | 6.86 | 0.86 | <0.001 |
Variable | Estimate | Standard Error | p-Value |
---|---|---|---|
Intercept | 19.99 | 18.44 | 0.283 |
MOE | 6.52 | 2.07 | <0.001 |
Group 2 vs. 1 | −11.91 | 20.75 | 0.568 |
MOE * Group | 0.33 | 1.71 | 0.846 |
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Nowak, T.; Patalas, F.; Karolak, A. Estimating Mechanical Properties of Wood in Existing Structures—Selected Aspects. Materials 2021, 14, 1941. https://doi.org/10.3390/ma14081941
Nowak T, Patalas F, Karolak A. Estimating Mechanical Properties of Wood in Existing Structures—Selected Aspects. Materials. 2021; 14(8):1941. https://doi.org/10.3390/ma14081941
Chicago/Turabian StyleNowak, Tomasz, Filip Patalas, and Anna Karolak. 2021. "Estimating Mechanical Properties of Wood in Existing Structures—Selected Aspects" Materials 14, no. 8: 1941. https://doi.org/10.3390/ma14081941