Proceedings e report - Firenze University Press

Material
FLEXURAL STRENGTHENING OF OLD WOOD MEMBERS IN HISTORICAL BUILDINGS WITH GFRP
GFRP
Epoxy resins
Table 1. Mechanical characteristics of the reinforcement material (reported by producer)
Modulus of
elasticity
(E)
MPa
76000
2000-5000
Failure
stress
(σ)
MPa
2000
35- 100
Ultimate
strain
( є )
mm/mm
2.60
1-60
304
Poisson's
Ratio
(V)
0.22
0.35-0.40
Density
(ρ)
g/cm 3
2.60
1.10-1.40
3.4. Test set-up
In this experimental investigation, three-point loading bending tests were performed as shown in Fig. 2
according to ASTM D-143 [9] for finding out the flexural strength. The simply supported test method
was selected to simplify the experimental setup. The wood specimens were supported at the butt and
the tip, and the load was applied at the centre through a bearing block on the tangential surface nearest
the pith Fig. 2 (b).
(a) (b)
Fig. 2 – Static bending test assembly. (a) Testing apparatus, (b) sample assembly and loading
The free span between the two supports was Ls = 360 mm for a total length of the specimen of L=
410 mm. These spans were established in order to maintain a minimum span-to-depth ratio of 14. Both
supporting knife edges were provided with bearing plates and rollers of such thickness that the
distance from the point of support to the central plan is not greater than the depth of the specimen Fig.
2 (b). The knife edges were adjustable laterally to permit adjustment for slight twist in the specimen.
During the process of loading, test data were transferred to a computer that was programmed to collect
and analyse all the data received from a load cell, connected to the Instron testing machine as shown in
Fig. 2. The bending tests have been carried out for a series of control (un-reinforced) beams and for
GFRP reinforced beams with varying area fraction of fiber reinforcement, as shown in Table 2.
Table 2. Mean dimensions of mid-span cross section for timber beams, reinforced with GFRP.
Samples No.of specimen Width (mm) Depth (mm)
Control 5 25.17 25.13
1 layer bottom 5 24.87 25.51
2 layers bottom 5 25.13 26.24
2 layers bottom +1 layer top + 2 strip 5 25.34 26.68
3 layers bottom 5 25.58 26.44
3 layers bottom + 1 layer top 5 24.79 27.70