Timber-concrete composite systems are a high-performance alternative for building floors, of great interest in the current context of environmental concerns. Looking for a more eco-friendly solution, the paper presents a new flooring system with a wood-concrete connection that does not require adhesives or special metal elements. Four-point bending tests were performed on TCC flooring samples with a span of 6.0, 7.2 and 8.4 m. Its cross section was a prefabricated piece in the shape of an inverted T made up of a lower glulam flange, glued together with a central plywood rib with aligned holes in its upper part that go through the entire thickness of the plywood. The set was completed with a top layer of poured-in-place concrete. The connection between both materials is achieved by penetrating the concrete into the rib holes. Additionally, corrugated steel bars were placed through said holes to achieve ductile behaviour. In all cases, a slenderness ratio of L/24 was used. The experimental results showed that the lowest value of ultimate load obtained was 4.3 times higher than the total service load estimated for a building for public use (9 kN/m2). The maximum deflection of the total load was between L/573 and L/709 for the loads corresponding to a building for public use (9 kN/m2) and between L/1069 and L/1340 for the case of residential type building (5 kN/m2). An analysis of the effects of vibrations in the service limit state in relation to user comfort has been included. The results indicate that the system satisfies the requirements for the intended uses.
Consequently, the proposed solution shows its effectiveness both in terms of strength and stiffness for the construction of light floors, being easy to build and having high performance.
This paper deals with the influence of the rolling shear deformation on the flexural behavior of CLT (Cross-Laminated Timber) panels. The morphological configuration of the panels, which consist of orthogonal overlapped layers of boards, led to a particular shear behavior when subjected to out-of-plane loadings: the low value of the shear modulus in orthogonal to grain direction (i.e., rolling shear modulus) gives rise to significant shear deformations in the transverse layers of boards, whose grains direction is perpendicular with respect to the tangential stresses direction. This produces increases of deflections and vibrations under service loads, creating discomfort for the users. Different analytical methods accounting for this phenomenon have been already developed and presented in literature. Comparative analyses among the results provided by some of these methods have been carried out in the present paper and the influence of the rolling shear deformations, with reference to different span-to-depth (L/H) ratios investigated. Moreover, the analytical results have also been compared with those obtained by more accurate 2D finite element models. The results show that, at the service limit states, the influence of the rolling shear can be significant when the aspect ratios became less than L/H = 30, and the phenomenon must be accurately considered in both deflection and stress analysis of CLT floors. Contrariwise, in the case of higher aspect ratios (slender panels), the deflections and stresses can be evaluated neglecting the rolling shear influence, assuming the layers of boards as fully-connected.
The flexural behavior of CLT panels was experimentally studied. The effects of number of layers, thickness and wood combination on the failure modes, ultimate bearing capacity, stiffness, and ductility of the specimen were analyzed. The test results showed that the flexural strength of the hybrid CLT specimens was basically unchanged, but the stiffness increased by 8% to 22% compared with the CLT specimens of all poplar wood. Compared with the CLT of the whole Douglas fir, the failure mode of the hybrid specimens changes from brittle shear failure to ductile bending failure. Furthermore, the calculation formula of the bending bearing capacity under various failure modes was proposed. The analytical results agreed well with the test results.
Bamboo-like glulam beams with hollow section units and intermittent internal reinforcement pieces were produced with small-diameter larch-wood pieces and one-component polyurethane. To better understand the design reliability, the failure mode, ultimate bearing capacity, and application potential were evaluated. Three types of beams (solid glulam, hollow glulam, and bamboo-like rectangular glulam beams) were compared and analyzed in this work. Stiffener pieces glued inside the bamboo-like beam were found to increase the bearing capacity and improve the failure mode relative to the hollow glulam beam. Comparison of the hollow section with a similar outside diameter showed that the ultimate bearing capacity increased by approximately 12.3% when the spacing between the stiffeners was 270 mm, and the ultimate bearing capacity increased by approximately 18.0% when the spacing between the stiffeners was 135 mm. Compared with the solid timber beams, wood consumption was reduced by 26.4% and 25.7% for the hollow and bamboo-like glulam beams, respectively. Also, a parameter analysis of the reasonable spacing and thickness of the stiffener was proposed by the finite element method.
The recent increasing trend of sustainable construction and advancement in the manufacturing of engineered wood have made products such as glued-laminated timber (glulam) and cross-laminated timber (CLT) preferred building materials. The intensifying demand for engineered-wood products in Canada also has prompted amendments to the building codes of several provinces by reducing the height restriction of timber structures from four to six stories. Unfortunately, the design of built-up timber beams has not yet been incorporated in most wood design standards worldwide. Thus, this lack of design guidelines brings forth the demand of acceptable methods to analyze, design and manufacture such built-up beam sections. The experimental research study detailed here in this thesis has been carried out to investigate the flexural bending behaviour of built-up glulam box-section beam assemblies fabricated using two engineered-control techniques at both, ambient and elevated temperatures. Seven full-size built-up glulam beam test assemblies were experimentally examined under four-point flexural bending to determine their maximum bending strengths at ambient temperature. Five of the seven beam assemblies tested at ambient temperature were fabricated using self-tapping screws; while the other two assemblies were built using industrial structural adhesive. The outcomes of ambient testing showed that reducing the spacing from 800 mm to 200 mm for the screws connecting the built-up beam section’s top and bottom flange panels to the web panels increased the beam flexural bending strength by about 45%. While reducing the spacing from 200 mm to 100 mm only for the screws connecting the bottom flange panel to the web panels over a distance equal to one-third beam span length from each support, where shear stresses are maximum, increased the beam flexural bending strength by an additional 10%. However, the experimental results of the glued beam assemblies showed considerable flexural bending strengths that are almost equal to the calculated strength of an equivalent hollow-section glulam beam. The influence of the bonding technique and configuration followed in fabricating the built-up beam sections, whether screwed or glued, was also investigated through observing the different failure modes that the built-up beam assemblies exhibited during testing. In addition, the experimental results of the ambient tests were used to verify the calculated bending strength capacity of the built-up glulam beams. Out of each of the glued and screwed assembly groups, only the strongest built-up beam assembly was examined under the effect of CAN/ULC-S101 standard fire while subjected to monotonic loading that was equivalent to the full-capacity design load of the weakest screwed built-up beam assembly with 200-mm screw spacings. The fire resistance tests were conducted using the large-size fire testing furnace accommodated at Lakehead University’s Fire Testing and Research Laboratory (LUFTRL). Outcomes of the fire resistance tests revealed that the glued built-up beam assemblies experienced greater mid-span deflections as well as beam end rotations in comparison to the screwed built-up beam assemblies. This inferior behaviour can be interpreted to the low fire resistance of the adhesive used in fabricating the built-up beam assemblies, which excessively limited the beam’s shear and bending strengths at elevated temperatures. On contrary, the self-tapping screws noticeably helped in keeping the built-up beam assemblies intact for longer time during fire testing even when the screws were exposed to direct fire heating.
In the last 15 years timber-concrete composite (TCC) systems have gained market share around the world. To facilitate acceptance of this construction method and to set basis for building TCC bridges in the Province of Quebec, the authors conducted a test program on TCC beams with continuous shear connectors. It included push-out tests on the connection and static bending tests on single-T TCC beams with 4-m and 12-m span and on double-T beams with 4-m span. The goal was to study the elastic and post-elastic performance and failure induced by the connector, analyse the relationship between the interface slip and the flexural behav iour and compare the test results with the predictions using design and analysis methods. The tests on beams with the continuous shear connector showed that it is possible to achieve high degree of the composite action between the concrete slab and timber beam followed by plastic deformation and failure of the connector inducing a ductile performance of the beam required in bridge design. The use of linear and non-linear analysis methods allows predicting the observed structural response of the TCC beams.
An extensive body of research is currently available on the behaviour of concrete and steel structures when subjected to blast threats, however, little to no details on how to address the design or retrofitting of wood structures are available. In this paper, preliminary results, both experimental and analytical, are presented on the flexural behaviour of glulam beams under high strain rates. A total of three 80 mm x 228 mm x 2,500 mm glulam beams with a clear span of 2,235 mm were subjected to simulated blast loads using a shock tube. The preliminary experimental results showed that a brash tension failure mode was observed on the tension laminate. It was also shown that a simplified SDOF model, using linear elastic resistance curves, was capable of predicting the failure displacement and level of damage with reasonable accuracy.
The glulam is determined by, and therefore a representation of, a new kind of ecological structural materials. The aim of this study was to summarize the mechanical performance especially the flexural behavior of various kinds of glulam and the physical properties of their relevant original timbers including pseudotsuga menziesii, larch, Yi poplar, poplar, China fir, mongolian scotch pine and camphor. And then it established and analyzed the relationship between the two to contrast those timber species so as to provide engineers with some reference in selecting timber glulam.