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10000 10500 11000 11500 12000 12500 13000 13500 14000 14500 15000 15500 MoE obtained with non-destructive method (MPa)

Figure 3. Correlation between MoE given by non-destructive test and MoE given by the mechanical evaluation.

.2166MoE (Sylvatest) + 8886.5

10000 10500 11000 11500 12000 12500 13000 13500 14000 14500 15000 15500 MoE obtained with non-destructive method (MPa)

by a constant bending moment zone and a maximum shear-to-bending moment ratio. This test uses a simply supported piece with a span of 18 times the depth, with the loading points placed on the third of the span. Because of the large span needed for the correct execution of the bending tests (18 times the depth), only the rafters and the tie-beams were tested. Results of the four-point bending tests are reported in Table 4.

3.3.6 Analysis and discussion of NDTresults Using UNI 11035 standards it was possible to visual strength grade the timber trusses. In particular, a strength class was assigned and a mean value for the modulus of elasticity (MoE) was suggested. Three values for MoE were founded: 12000 MPa, 10500 MPa and 9500 MPa corresponding to strength class S1, S2 and S3, respectively. For visual grading, it was necessary to record the moisture content and to calculate density.

During the visual inspection, significant variation in cross-section geometric properties was founded. Turrini-Piazza hardness test permits the correlation between the load force (R) required to embed a steel bit into the wood with MoE. However, the evaluation of a reduction factor dependent on the defectiveness of the element is required. This reduction factor was calibrate (with a value of 0.6) using near 1000 tests results and the MoE values obtained with the mechanical evaluation. Apart this capability of the test, it was tried to correlate the load force (R) with the density. The correlation obtained is poor (r2 = 0.35) despite the significant values used. Others researchers have tried to correlate the Resistance Measure (RM), obtained with the resistograph test, with density. The same attempt was made but the correlation obtained is very poor (r2 = 0.02). A correlation coefficient of 0.5 was obtained for the correlation between the depth of penetration measured with the Pilodyn and the density. In conclusion, and assuming as reference values for the MoE the results of the mechanical tests, a correlation between all non-destructive tests able to predict this property and that values were defined, and presented in Figure 3.

Figure 3. Correlation between MoE given by non-destructive test and MoE given by the mechanical evaluation.

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