Proceedings e report - Firenze University Press

WOOD SCIENCE FOR CONSERVATION OF CULTURAL HERITAGE
The mid-span displacement, failure load, stress at rupture and modulus of elasticity have been
measured automatically by a purposely written computer program . see Fig. 2 (a and b) and Table 3.
The approximate moisture content of the samples at the time of reinforcement application was 12%
and the relative humidity of the lab during the test was 50%.
4. Results and Discussion
4.1. Control specimens
According to the field of investigation, Zelkova serrata wood was the most useable material for
structural elements in a high percentage of ancient buildings; therefore this wood has been selected for
study. The results of the tests for control specimens are shown in table 3. In this test, the mid-span
deflection, load capacity, modulus of elasticity in range of the 25% to 75% of the elastic region and
the mode of failure were evaluated.
Specimen
Number
Table3. Experimental results of control (un-reinforced) samples.
Displacement
at rupture
(mm)
Load at
rupture
(kN)
305
Stress at
rupture
(MPa)
Modulus of
elasticity
(Nmm -2 )
1 16.46 3.92 131.80 9721
2 11.22 3.70 127 11740
3 11.59 3.22 110.10 9495
4 10.85 3.41 116.40 10440
5 12.79 3.32 111.20 8554
Mean: 12.58 3.51 119.30 9990
S.D. 2.29 0.29 9.70 1186
4.2. GFRP-Wood hybrids
It should be noted that at first, some samples were tested with short length reinforcement only on the
high moment zone, but the results obtained were not satisfactory. For this reason, all the other tests
have been conducted with full length bond with size of 410 mm long.
In this case, the reinforcement of wood, with glass fiber reinforced polymer caused a considerable
increase in strength and stiffness under bending test. The load-displacement curves for different
schemes of reinforcing are shown in Fig. 4 (a to e).
The results of this investigation have shown that the load-displacement behaviour of all the control
specimens and low fraction of reinforcement samples, like one and two layers, are almost linear up to
the failure point, as shown in Fig. 3a and 3b. However, for those with more than two layers of
reinforcement the behavior changes toward nonlinearity, as shown in Fig. 3(c to e).
The samples under test experienced either a brittle tensile collapse or a ductile compressive failure. All
control specimens and those reinforced with up to two layers of GFRP failed on the tension side. The
samples reinforced with three or more layers of GFRP showed ductile compressive failure.
The test results have shown that the effect of GFRP composite reinforcement on the mechanical
properties of GFRP-wood hybrid is positive. In all the experimental cases there was a significant
increases in the strength and stiffness of the reinforced specimen, compared with the control. The most
effective results in GFRP-wood hybrid were obtained when the specimens were reinforced with three
layers of GFRP on the tension side, and one layer on compression side, as shown in Fig. 3e. In this
case, load capacity, stress at rupture and the modulus of elasticity increased by 57.10, 31.26 and
9.61%, respectively when compared with control specimens, as shown in Table 4.