Proceedings e report - Firenze University Press

WOOD SCIENCE FOR CONSERVATION OF CULTURAL HERITAGE
During the last two decades, a special prefabricated fiber reinforced polymer (FRP) composite was
developed to repair and retrofit wooden elements in the field. The advantages of these reinforcing
materials lie in their low weight, high tensile strength and resistance to corrosion. According to recent
investigations, FRP materials have been successfully used to strengthen existing structural members.
Svecova and Eden (2004) tested timber beams reinforced with GFRP dowel bars as shear
reinforcement as well as flexural bars to avoid the tension failures observed in some of the specimens
[1]. Amy and Svecova (2004) presented an economical rehabilitation scheme to strengthen creosotetreated
timber beams in both flexural and shear with glass fiber reinforced polymer bars [2]. Borri et
al. (2005) presented a method for flexural reinforcement of old wood beams with CFRP materials.
Mechanical tests on the reinforced wood showed that external bonding of FRP materials may increase
flexural stiffness and bending capacity [3]. Corradi et al. (2006) presented in-plane shear
reinforcement of wood beam floors with FRP [4]. Buell et al. (2005) presented an investigation on
reinforcement timber bridge beams with a single Carbone-FRP (CFRP). A 69% increase of bending
strength was reported when compared with control beam and a compression failure mode [5].
Calderoni et al. (2006) presented an evaluation of flexural and shear behavior of ancient chestnut
beams under both experimentally and theoretically. The results have shown that the simplified
methods commonly used to evaluate the bearing capacity of wooden beams can be safely applied to
ancient structural members [6]. Dagher (2005) introduced current state of the art of reinforced wood
technology, new products, codes and specifications [7]. Corradi and Borri (2007) presented a study on
Fir and Chestnut timber beams reinforced with GFRP pultruded elements and the tests showed that the
reinforcement with GFRP beams produced significant increase in flexural stiffness and bending
capacity [8].
The purpose of this study is to present a new innovative technology, based on glass fiber reinforced
polymer composite (GFRP) sheets, for the on-site rehabilitation of the old wooden members in
historical buildings, through testing of small size wooden members and comparing the experimental
results with numerical calculation.
3. Materials and methods
3.1. Wood Materials
This experimental test is based on more than 50 specimens of ancient Zelkova serrata (Celtic
Occidentalis) which is a hardwood. These specimens have been obtained from newly replaced and
crushed structural elements of a historical building, located in the town of Babol, near the Caspian
Sea, built up almost 150 years ago. Because of the limitation of obtaining enough old wood for testing
and also because of major defects present in the main wood, like longitudinal splitting, cracking,
degraded zones and holes due to nailing and insects attack, the samples were obtained in size of
25× 25× 410 mm, and tested according to ASTM D143 for small clear specimens of reinforced
timbers [9].
3.2. GFRP Materials
In recent years FRP has been used as a compatible reinforcement material for timbers and plywood.
The physical/mechanical/chemical properties of the FRP are very versatile. The FRP may be
engineered to match and complement the orthotropic properties of wood; consequently,
incompatibility problems between the wood and the reinforcing FRP are minimized. A unidirectional
pultruded glass fiber-reinforced-polymer (GFRP) sheet with a thickness of 0.16 mm in size of 25× 410
mm was used, having the physical and mechanical characteristics reported in Table 1, as provided by
the producer.
3.3. Resins
The adhesive used in this test was Mac epoxy glue, which consisted of two parts, resin and hardener,
mixed in the ratio of 3:1 by volume volume. The mechanical properties of the epoxy resin are reported
in Table 1.
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