Advanced Materials Research Vol. 778

Abstract: This paper presents an analysis on the viability of the use of natural fibres, in particular sisal fibres, as a reinforcing material in wood laminate structures. The use of natural fibres associated to the manufacturing of beams, with wood from reforestation, is in accordance with the current economic interest and ecological appeal. Sisal fibres have attracted attention for presenting adequate mechanical characteristics for such application. The laminated beams used in this research were constituted by Pinus sp and were reinforced by sisal strips with a thickness of 2 mm glued by Epoxi adhesive on bottom of the beam on the tensile region. Each lamina had the following dimensions: width of 50 mm, height of 20 mm and the length of the beam is 1.5 m. For the theoretical analysis of wood laminate beams three models: stress functions, classical lamination theory and section transformed method are carried out. It was noted that the average differences between the theoretical results and experimental data are given by: 11% and 2 % for normal and shear stresses respectively, and around 8%, for displacements. As a conclusion, the strengthening of wood laminate beams with sisal fibres is effective in wood structural elements, in which the elastic modulus is at maximum equal to these fibres and also prevents fragile failure on critical tensile region.

Abstract: Compatibility and durability are fundamental aspects to take into account when dealing with strengthening and repair of structural components in existing buildings. In particular, timber elements in floors and roofs, like beams and joists, can be improved in their load-bearing capacity by the use of composite (fiber-reinforced) materials. Applied as textiles or laminates, those materials can provide additional tensile strength without weight increase, and are easily applied in situ. Recently, an increasing interest towards the biocomposites (flax, hemp) opened new perspectives: the advantages in comparison with traditional FRPs includes the higher mechanical compatibility and sustainability, especially if glues suitable for wood (e.g., vinyl) are used as matrix, instead of epoxy resins.In the paper, the results of an experimental campaign carried out at the University of Padua, aimed at investigating the influence of humidity and temperature on the adhesion of composite materials (carbon or glass FRP) and biocomposites (flax) reinforcing spruce timber elements are presented. Epoxy resins were used as matrix for all composites; flax was also applied with vinyl glue and considering a protective treatment (alkaline-based). Effectiveness of bond at the interface timber-reinforcement was measured by pull-off tests, and analyzed at micro-structural level by optical microscopy and infrared spectroscopy.

Abstract: Durability on structural function of a carbon fiber reinforced member was evaluated with various environment tests. In this research, the relations between the environmental factor, such as the temperature and humidity, and the strength properties were analyzed firstly using heat cycle test and natural exposure test. Durability was analyzed from the viewpoint of the strength deterioration in the bonded part. A mechanism of deterioration for the decrease of the bond strength to influence the decrease in the bending strength was indicated. Finally, an evaluating method of carbon fiber reinforcement was shown through this study.

Abstract: Composite systems used for increasing the load bearing capacity of timber structural elements are of special interest for engineers, basically because of their beneficial weight/strength ratio. By creating a hybrid cross section composed of wood and interposed GFRP lamellae, the improvement of wood limited elastic properties may be achieved, considering the compatibility between composite materials matrix, thermosetting unsaturated polyester resin, and wood. The main objective of the paper is to carry out an experimental study on the technical solution represented by associating these two materials with similar structures, both pertaining to the class of composites reinforced with long fibres and bonded, for the case of wood by lignin and hemicelluloses and for the case of GFRP by unsaturated polyester resin. The experimental program consists in performing the bending test of timber beam type structural elements, considering two types of cross-sections, the first being composed by joining three timber boards of 25x100x1900 mm by aid of screws and the second, with wood/GFRP hybrid cross-section, having the same number of timber boards as specified above joined together by two 3...5x100x1900 mm GFRP interposed lamellae. Determination of some physical and mechanical properties, in the laboratories of Faculty of Civil Engineering and Building Services, Iasi, Romania and the obtained results are comparatively presented for the two types of tested beams, the final step of the paper consisting in optimizing the technology involved for execution of the hybrid structural element.

Abstract: Brazil cultural heritage is composed by numerous constructions that describe the various historical periods lived by country. Constructions arent in good conservation status, showing systematically some deterioration level of their structural elements, among them those of wood. Restoration process aims to preserve the identity of original cultural heritage. It is essential maintain structural characteristics related to mechanical loads response which are closely dependent on wood properties avoiding possible structural shocks. Wood deterioration can be characterized by fungi decay or termite attack. Depending on level and position of the deteriorated area in structural set, local interventions are enough to maintain structural integrity. Polymeric resins are material options that can be used when removed these deteriorated regions, requiring compatibility with wood to maintain structural elements properties. This paper aims use of a technical for restoring structural timber from historic buildings, based on removal of decayed regions and filling them with epoxy resin. To analyze restoration effectiveness, properties in static bending, according to Brazilian standard, were determined. Samples were produced containing one and three restorations along the specimens (105 cm in length and nominal square cross section of 4.5 cm side), on the same side. Samples of Pinus taeda with gaps generated in the specimens with dimensions of 1.10 cm in depth and 8 cm in length were tested, with restorations placed in central region. For grafting of these gaps bicomponent epoxy resin was employed, prepared by mixing components in 1:1.5 proportions. Resin was injected into splices and its cure occurred in a seven days period, using methodology restoration to simulate a situation in which these structural elements have been used. Samples were requested in static bending to obtaining the product of inertia, analyzing the amendment under the aspect of tractioned and as well under compressed edge. It is observed the viability of restoration using filling epoxy resin in timber samples, considering the mechanical performance and practicality of the methodology for local keeping.

Abstract: In this paper a non-invasive technique for the repair of ancient wooden floors is presented. Steel plates are glued on one side only by epoxy-adhesive into longitudinal grooves in order to allow the free swelling and shrinkage of the wood in the direction transversal to the plate glueing surface, thus reducing the risk of plates’ delamination. A set of high strength steel nails guarantees the transmission of the load from the steel plates to the wooden beam in case of loss of adhesion due to fire or delamination. This technique was used to repair a precious beam in a wooden floor of the 15th century in Palazzo Calini (Brescia, Italy). The presented technique requires particular attention because it might be affected by the delamination of the glued reinforcement due to the stress concentration, which occurs at the end of the repairing element or at the cracks of the repaired beam.The main results of experimental and numerical studies focusing on the delamination phenomenon are also presented and discussed. They have shown that the risk of plate debonding can be markedly reduced by the capability of the sapwood to develop plastic strain. The wooden floor has been monitored for more than eleven years, confirming the effectiveness of the adopted technique. The monitoring has also shownthe importance of limiting the wooden moisture content variation to reduce the floor’s creep deflection.

Abstract: This paper presents and discusses the possibility of improving the bending strength of timber beams through the use of prestress. The emphasis is put on various methods of imposing the prestress force and transferring it into the wood part: i) through post-tension, with the force being mechanically anchored on the ends of the wood elements; ii) through pre-tension, with the anchorages being either mechanical, as in the previous system, or glued, with the force being gradually transferred through shear stresses along a certain length of the wire/wood interface. Although the risk of failure due to tension perpendicular to the grain in the anchorage regions exists, it is not specifically studied in here, due to the limited scope of the study. The main conclusion is that any of the procedures may be advantageously used with either small (mass-production) or large-span glued-laminated timber beams and, though they are mostly suited to the production of new elements, they may also be adapted to the strengthening of existing beams.

Abstract: In refurbishment operation of existing timber floors could prove of some interest the possibility of hogging the existing timber beams, in case of the presence of excessive permanent midspan deflections. In the case of sagged timber floors which cannot be buttressed due to heritage issues, the possibility of cambering a timber beam by simply putting another wooden beam on the top of it and inserting screws inclined at 45° relative to the beam axis has been experimentally investigated, with some promising result. The cambering procedure has proved to be more effective when the fastener are inserting starting from the internal part of the beam, permitting to obtain significant values of upward deflection (it has been observed an upward deflection of about one three-hundredth of the total beam length): the values could possibly be increased by reducing the screw spacing or by using fasteners able to generate a greater pressure. The effectiveness of this method is based on the capability of self-tapping screws to induce internal stress in timber element during the drilling procedure: the horizontal component of the resultant pressure yielded by the inclined screws is directly related to the possibility to hog the composite system. The aim of the experimental campaign described in this paper was to investigate the values of the internal stress induced by different type of fasteners during the drilling procedure, studying the influence of different parameters such as screw angle with respect to the grain direction, initial pressure, head penetration length, threaded part length, connector typology, wood density, time-dependence.

Abstract: This paper presents the laboratory work performed with the purpose of understanding the mechanical performance of 340x20x20 mm maritime pine wood samples degraded by rot fungi when treated with a biocide product followed by consolidation through impregnation with a polymeric product.Four commercially available products were used: a water-based biocide, BC, a solvent-based biocide, X, an acrylic consolidant, PB (PB 72), and an epoxy-based consolidant, E.Seven sets of specimens each one having a varied range of fungal degradation were prepared. Then the product combinations were applied by brush to six sets of specimens (E, X-E, BC-E, PB, X-PB, BC-PB) of which one was left untreated for control, 0-0. Finally all sets were subjected to static bending strength test until rupture.Results showed that the acrylic and epoxy-based products lead to increased mechanical capacity of the consolidated wood up to 100% in some cases in specimens with 70% of MOE loss. The results presented the same order of magnitude for both wood consolidants. The previous application of biocide did not have a significant impact in the behavioral pattern of the consolidant: a marked improvement of the bending strength of the degraded specimens after treatment and consolidation. These results demonstrated the feasibility of combining biocide/consolidation products, and provide indications of interest to the application of this technique to extend the lifespan of wood elements moderately degraded by fungi in old buildings.

Abstract: A pilot experiment of microwave treatment was carried out on an Art Nouveau residential building erected at the beginning of the 20^th century in Valencia, Spain. The timber structure was affected by a combined damage caused by Anobium punctatum (common furniture beetle or common house borer) and Kalotermes flavicollis (yellownecked dry-wood termite). After performing an exhaustive preliminary study on the building and analyzing the different alternatives of wood treatment, it was decided to use a microwave machine especially designed to eliminate this type of wood boring insects.This machine generates microwaves, a type of electromagnetic radiation, with a frequency of 2.45 GHz. This circumstance makes it possible to produce a high-frequency alternating electric field that causes the rotation of the molecular dipoles of water. Because of this continuous rotation the temperature of the water rises considerably.By heating up the humidity inside a living being, as in the case of xylophagous insects, an artificial fever in the body is generated, and since the animal is not capable of tolerating this temperature, it dies.In order to eliminate xylophagous insects, the wood moisture content (usually between 10% and 12%) and the presence of water in wood boring insects (around 90%) must be taken into account. Due to the greater content of humidity the increase of the temperature is higher and quicker in insects than wood.After having studied and experimented with different combination of power and time of exposition to the microwaves, this machine was found capable of eliminating any type of insect that may live inside the timber without harming the wood itself.Prior to this pilot intervention, several research works were carried out with the same microwave machine, both on structural timber and wooden works of art. In all these studies it was observed that no damage was caused either to the wood or to the finish of the works of art including pigments, polishes, stains etc. On the other hand, 100% efficacy was achieved in the elimination of xylophagous insects.This article describes the design, experimentation and perfecting process of this microwave machine and its pilot application on structural timber in an Art Nouveau residential building. As an example of method, the intervention followed the main steps of diagnosis and treatment testing including the analysis of several options of intensity and time that led to the positive final results obtained.