This paper provides understanding of the fire performance of exposed cross-laminated-timber (CLT) in large enclosures. An office-type configuration has been represented by a 3.75 by 7.6 by 2.4 m high enclosure constructed of non-combustible blockwork walls, with a large opening on one long face. Three experiments are described in which propane-fuelled burners created a line fire that impinged on different ceiling types. The first experiment had a non-combustible ceiling lining in which the burners were set to provide flames that extended approximately halfway along the underside of the ceiling. Two further experiments used exposed 160 mm thick (40-20-40-20-40 mm) loaded CLT panels with a standard polyurethane adhesive between lamella in one experiment and a modified polyurethane adhesive in the other. Measurements included radiative heat flux to the ceiling and the floor, temperatures within the depth of the CLT and the mass loss of the panels. Results show the initial peak rate of heat release with the exposed CLT was up to three times greater when compared with the non-combustible lining. As char formed, this stabilised at approximately one and a half times that of the non-combustible lining. Premature char fall-off (due to bond-line failure) was observed close to the burners in the CLT using standard polyurethane adhesive. However, both exposed CLT ceiling experiments underwent auto-extinction of flaming combustion once the burners were switched off.
This study investigates timber connections with flexible polyurethane adhesives, which prove to have the potential for timber-adhesive composite structures without mechanical connections for seismic regions. Results of conducted cyclic double lap-shear adhesive timber joints tests were compared with available experimental results on timber connections with standard mechanical dowel-type fasteners and with results of numerical finite element analysis. The study found that the shear strength, elastic stiffness and strength degradation capacity of the flexible adhesive connections were significantly higher compared to mechanical fasteners commonly used in seismic-resistant timber connections. The latter, however, manifested larger ultimate displacements but also yielded at lower displacements.
Cross laminated timber (CLT) is becoming widely available in North America. The product standard for North American CLT, PRG-320, has strict requirements on adhesive performance under fire scenarios. To become an adhesive certified under PRG-320, a full sized CLT compartment must be built and tested without a second flashover occurring caused by delamination. Currently, only three adhesive formulations are PRG-320 certified. This large scale test is expensive to run and only yields “pass-fail” results. In this paper we present small-scale adhesive tests performed at the Forest Products Laboratory. The tests examine a single lap shear joint. The samples are tested at elevated temperatures in a universal testing machine with an environmental chamber built around the grips. The strains are measured using digital image correlation. Tests were conducted in two different manners. In the first test, thermal equilibrium was achieved and the sample was loaded to failure. In the second test, a constant load was applied and a thermal ramp was applied until failure occurs and the temperature at failure was recorded. Importantly, the tests were compared against control samples of solid wood (no adhesive) so that adhesive strength could be normalized to that of solid wood. It is hoped that this small-scale test can aid in the understanding of CLT adhesive performance and be used to screen adhesives prior to investment in large scale adhesive qualification tests.
European Journal of Engineering Research & Science
Summary
An analysis into the flexural strength of solid and laminated timber specimens under working conditions was conducted. Five hardwoods and five softwoods were investigated, namely: Mansonia, Mahogany, Orji, Ukpi, Ufi mmanu, White Afara, Owen, Melina, Akpu and Ubia. The dimensions of the wood specimens are 100mm×50mm×20mm. The wood samples were tested for flexural strength using a Universal Testing Tensile Machine. The results obtained shows that Owen has the highest ultimate wood strength of 46.806N/mm² for the softwood glulam. Ukpi has the highest wood strength of 73.375N/mm² for the hardwood glulam, and highest MOE at 2412.93N/mm². Akpu recorded the weakest sample with bending strength values for glulam at 11.929 N/mm². Comparisons of strength were made to their respective solid timbers. Failure modes were analyzed. The study therefore demonstrates that the timber species used can be engineered to load bearing glulam structural elements using polyurethane adhesive glue without severe loss of strength.
Eucalyptus grandis is South Africa‘s most important commercial hardwood species. The availability of E. grandis and its fast growth rate creates the opportunity to explore its uses further. Cross-laminated timber (CLT) is a prefabricated multilayer engineered panel product made of at least three layers, with the grain direction of some or all of the consecutive layers orthogonally orientated. In order to add value to E. grandis, reduce the export of low-cost chips, increase the profit margins of local plantation owners and create jobs, the development of E. grandis CLT in South Africa may be an option. There is concern among some researchers that the bonding quality evaluation tests proposed by CLT standards have been developed for glulam and are too severe for CLT. These researchers proposed that further analysis and possibly even revision of the test methods should be considered. There is also a need to evaluate the mechanical properties of CLT panels made of E. grandis to completely understand the structural performance of these panels, including their bond quality and durability, and therefore be able to rely on E. grandis CLT as a construction material. The objectives of this study were: . To evaluate the face-bonding quality of CLT panels from E. grandis timber bonded with a one component polyurethane resin; . To determine the influence of material and processing parameters on the face-bonding quality of CLT manufactured from E. grandis timber bonded with a one component polyurethane resin; . To analyse different testing methods for evaluating the face-bonding quality of CLT. The design for this experiment consisted of eight groups with different combinations of parameters for density, grooves and pressure per group. Four different testing methods were used to evaluate the face-bonding quality of CLT panels from E. grandis and to determine the effect of parameters on face-bonding quality: A delamination test on 100 x 100 mm block specimens (Test A), a shear test on 40 x 40 mm specimens (Test B), a shear test on 40 x 40 mm specimens with grain direction 45° to load direction (Test C) and a combined delamination and shear test on 70 x 70 mm specimens with grain direction 45° to load direction (Test D). Results of the statistical analysis indicated that E. grandis CLT made with 1C-PUR adhesive can obtain excellent face-bonding quality using a clamping pressure of 0.7 MPa and with no stress relief grooves present. All samples passed the shear test (Test B) which is the reference test method proposed by EN 16351 (2015). It was found that a strength component and durability component will be an advantage when testing the bond quality of CLT. Shear tests at 45° to the load direction did not completely eliminate the rolling shear effect. The combined delamination and shear test (Test D), seems to have potential as a good test for bond quality since it is a combination of a durability and shear strength test. There are still questions about the relative advantages of specific test methods for bond quality, especially on the effect of rolling shear. Further work should focus on this aspect and the use of stress models might be a way of gaining further insights.
Cross-laminated timber (CLT) became a popular engineered wood product in recent years for highquality and innovative timber buildings. As for any building product, the fire behaviour of CLT panels requires careful evaluation in the design of such buildings. The adhesive used in the bond lines of CLT plays an important role in the fire design. However, currently, European standards do not provide a test method to assess the adhesive performance in CLT exposed to fire. This paper presents a series of fire tests performed with CLT panels glued with different adhesives. It is shown how the mass loss of the CLT panels in standard fire resistance tests can be used to assess the adhesive performance in CLT exposed to fire.
The effect of blue stain on shear strength of cold-set polyurethane resin (PUR) bonds was investigated using lodgepole pine lumber with varying degrees of stain and two different wood grain orientations. While blue stain was associated with definite differences in wood permeability, it had no negative effect on shear strength or wood failure percent. The results indicate that blue stain will not adversely affect bond strength of PUR bonds.
In this study, flexuralbehaviors of glue laminated timber beams manufactured from Pinussylvestristree were investigated by comparing the results with those of massive timber beams. The main variables considered in the study were number of laminations, types of adhesive materials and reinforcement nets used in the lamination surfaces. In scope of the experimental study, glue laminated beams with 5 and 3 lamination layers were manufactured with 90 x 90 mm beam sections. In the lamination process epoxy and polyurethane glue were used. Morever, in order to improve the bond strength at the lamination surface, aluminium, fiberglass and steel wire nets were used at the lamination surfaces. Load–displacement responses, ultimate capacities, ductility ratios, initial stiffness, energy dissipation capacities and failure mechanisms of glue laminated beams were compared with those of massive beams. It was observed that the general bending responses of glue laminated beams were better than those of massive beams. In addition to that the use of reinforcement nets at the lamination surfaces increased the ultimate load capacities of the tested beams. The highest ultimate load capacities were oberved from the tests of glue laminated beams manufactured using five laminated layers and retrofitted with polyurethane glue using steel wire reinforcement nets, in the direction normal to the lamination surface. Finally, the finite element simulations of some test specimens were performed to observe the accuracy of finite element technology in the estimation of ultimate capacities of glue laminated timber beams.
This article presents a test method that was developed to screen adhesive formulations for finger-jointed lumber. The goal was to develop a small-scale test that could be used to predict whether an adhesive would pass a full-scale ASTM E119 wall assembly test. The method involved loading a 38-mm square finger-jointed sample in a four-point bending test inside of an oven with a target sample temperature of 204°C. The deformation (creep) was examined as a function of time. It was found that samples fingerjointed with melamine formaldehyde and phenol resorcinol formaldehyde adhesives had the same creep behavior as solid wood. One-component polyurethane and polyvinyl acetate adhesives could not maintain the load at the target temperature measured middepth of the sample, and several different types of creep behavior were observed before failure. This method showed that the creep performance of the onecomponent adhesives may be quite different than the performance from short-term load deformation curves collected at high temperatures. The importance of creep performance of adhesives in the fire resistance of engineered wood is discussed.
To better use the second-growth wood resources in value-added applications, this work addressed the manufacturing aspects of cross-laminated timber (CLT) products from western hemlock (Tsuga heterophylla (Raf.) Sarg) and amabilis fir (Abies amabilis (Dougl.) Forbes) (or hem-fir) harvested from coastal British Columbia, Canada. Small CLT billets (nominal 610 mm×610 mm) were made to examine CLT bond quality and durability through block shear and delamination tests. Two types of adhesives, single-component polyurethane (PUR) and emulsion polymer isocyanate (EPI) and two critical applied pressure parameters (0.28 and 0.83 MPa) were adopted to manufacture hem-fir CLT. It was found that the adhesive type and applied pressure significantly affected wood failure percentage (WFP) and delamination of hem-fir CLT. When PUR adhesive was used, CLT made at 0.83 MPa pressure yielded significantly higher WFP and lower delamination than that made at 0.28 MPa pressure. The results demonstrated that despite the fact that hem-fir lumber is not particularly specified in the current North American CLT standard, it could be used for manufacturing CLT with the required panel bond quality.
){kind=link}
){kind=link}