Glulam Timber Beams Research Articles

Numerical simulation and analytical study of glulam timber beams

Glulam beams or glued-laminated beams consist of sawn lumber laminations (timber) bonded with an adhesive material. This paper, through the mathematical description of the contact conditions that apply at the interfaces of glulam beams and the development of two three-dimensional finite element models by the use of the ANSYS software package, studies the flexural properties of unreinforced (UGB) and reinforced (RGB) glulam beams. The first computational model presents an unreinforced glulam beam that has been produced by three wood laminations of dimensions 6 by 3.6 by 176 cm. The latter one describes a reinforced glulam beam, which has been produced by gluing a 0.15 cm thick steel plate at the bottom edge of the previously described beam. The computational analysis indicates that the two glulam beams have significantly different bearing capacities under the same load and support conditions. The failure mode of the UGB is brittle whereas the one of the RGB is ductile. The numerical results of both models are in close agreement with experimental ones from the international literature. Keywords: Glulam Timber Beams, Numerical Simulation, Contact.

Numerical Modelling of the Initial Stress and Upward Deflection of Glulam Beams Pre-Stresseed by Compressed Wood

A new approach to reinforce glulam timber beams has been developed by using compressed wood (CW) which is made of a lower grade wood through densification processes. In the reinforcing practice, compressed wood blocks are inserted into pre-cut holes on the top of glulam beams to produce pre-camber and to generate initial tensile and compressive stresses on the top and the bottom extreme fibre of the glulam beam. In order to optimize the size, the number and the location of CW blocks, 3-D finite element models have been developed. 3D non-linear finite element models have been developed to simulate the pre-camber of Glulam beams locally reinforced by compressed wood blocks. The models developed have also produced the initial tensile and compressive stresses at the top and bottom extreme fibres with building-up moisture-dependent swelling on the CW blocks. With the pre-camber and the initial stress state that cancel out proportions of working deflection and stresses.

Prestressed glulam timbers reinforced with steel bars

This paper discusses a series of four-point bending tests that were conducted to failure on unreinforced, reinforced and reinforced-prestressed glue laminated (glulam) timber beams with steel-bars in a simply-supported scheme to determine their flexural behavior. The cross sectional ratio between the steel and the wood was 0.82%. To increase the level of reinforcement, some reinforced beams were prestressed by applying a moderate force to the lower bar. The experimental and numerical data provided the load–deflection, load–strain relationships and strain profiles of the tested beams. The results of the reinforced beams showed that the mechanical strength, the load-carrying capacity and the stiffness for both the simple and prestressed beams were enhanced compared to the unreinforced beams. For the simply reinforced beams, the stiffness increased by 25.9%, the ultimate load increased by 48.1% and the ductility increased by 43.8%. For the reinforced and prestressed beams, the stiffness increased by 37.9%, the ultimate load increased by 40.2%, and the ductility increased by 79.1%.

Elasto-plastic behavior of glulam timber beams with joints by prestressing

Elasto-plastic behavior of glulam timber beams with joints by prestressing

Flexural Reinforcement of Glulam Timber Beams and Joints with Carbon Fiber-Reinforced Polymer Rods

Fiber-reinforced polymer (FRP) composites have largely been used in combination with masonry and concrete structural elements in the last decade. Recent applications showed that new advantages may also be achieved in the field of timber structures, even if currently steel fasteners are used mainly in connecting systems. This study investigated the possibility of using carbon FRP (CFRP) rods as glued-in reinforcement of glulam beams and as glued-in connectors for glulam timber head joints that should transfer flexural moment between two adjacent beams. Half-scale beams were tested both with and without the presence of FRP reinforcement. Flexural behavior of CFRP-reinforced beams was compared with unreinforced beams that were used as control specimens. Two different amounts of CFRP reinforcement were used in the beam section. Experimental results showed a significant influence of the CFRP rods, because the reinforced beams demonstrated an increase in ultimate capacity and stiffness. Experimental results were also compared with numerical analysis, which showed good accordance with regard to the load and deflection values. Full-size head joints were prepared and tested. Flexural behavior of the joints was compared with the mechanical properties of monopiece beams that were used as reference specimens. Three different force transfer lengths were used for the construction of CFRP-timber joints. Experimental results showed that the use of CFRP rods in timber joints was successful, because the capacity of the CFRP-jointed beams was almost the same as that of the monolithic beams for the longest bond length that was adopted. This result is important in order to find an adequate alternative to traditional joints made with steel bolts and plates, which are unable to create rigid connections, increase dramatically the weight of timber structures, and may be subjected to corrosion in an aggressive environment. A numerical modeling based on the virtual work principle was also conducted and theoretical results were found in good accordance with the experimental results for the tested joint.

Factors affecting ultimate strength of solid and glulam timber beams

Phenol Resorcinol Formaldehyde is an adhesive commonly used in the fabrication of glued laminated (glulam) timber beams. Although, it has been widely accepted for softwood species, the verification of this type of adhesive for local timbers is not fully established. Four glulam beams and four solid beams were tested in bending in the laboratory. Phenol Resorcinol Formaldehyde was used as an adhesive for glulam beams. The strength of the glulam beam structure was equivalent to solid beam structure. Phenol Resorcinol Formaldehyde was able to provide sufficient bonding and strength for local timbers. The results indicated that the most significant factor influencing the strength of solid beam and glulam beam structure was the density of timber.

Suspended Roof for the Olympic Skating Arena, Nagano

The 18th Winter Olympics were held in February 1998 in Nagano, Japan, where the Olympic Memorial Arena was the venue for the speed skating competition. The arena, covering an area of 80 × 216 m, contains a 400 m speed-skating oval and seating for about 10,000 spectators.The most distinctive characteristic of the structure is its semi-rigid hanging roof that spans 80 m with a thickness of only 30 cm. The roof structure consists of fifteen suspended units, each composed of composite hanging beams with plywood panels fixed to them. Each composite beam is composed of two glued-laminated (glulam) timber beams sandwiching a steel plate.

Prestressed Glued-Laminated Timber Beam—Pilot Study

The performance of glued-laminated (glulam) timber beams may be improved by the addition of high-performance fibers between the laminations. The contribution of the fibers is further enhanced if they are pretensioned prior to incorporation into the glued-laminated beam. This research indicates that both strength and stiffness are increased by using small volumes of pretensioned Kevlar yarns. The research explores the bond, development, and adhesive performance associated with the prestressing operations.

Performance of Red Maple Glued-laminated Timber Beams

The objective of the research was to determine if red maple glued-laminated (glulam) timber beams with design flexural strength of 16.5 MPa (2400 psi) and design stiffness of 12.4 GPa (1.8 106 psi) could be designed and fabricated. The strength and stiffness of red maple glulam timber beams were predicted using ASTM D3737 procedures and then compared to data from 45 test beams, 15 each of 3 sizes. The results show that ASTM D3737 procedures conservatively predict the strength and satisfactorily predict the stiffness of red maple glulam timber beams and that red maple beams with flexural strength of 16.5 MPa (2400 psi) and stiffness (MOE) of 12.4 GPa (1.8 106 psi) are technically feasible. Also, the volume effect for the strength of the red maple glulam timber test beams was similar to the published volume effect for softwood glulam beams.

Transverse Isotropy Modeling of 3‐D Glulam Timber Beams

The mathematical modeling of glued‐laminated (glulam) timber beams is greatly simplified by considering the material to be isotropic in the plane of the cross section. In this paper, the hypothesis of transverse isotropy for southern pine glulam beams is verified through an experimental torsion program. Solid‐sawn samples of rectangular cross sections that exhibit rhombic symmetry were tested in torsion about their longitudinal axes (L) to compute the principal shear moduli in the radial (GLR) and tangential (GLT) directions. The small difference between GLR and GLT was indicative of the transversely isotropic behavior of southern pine beams. Based on this behavior, the shear moduli (G) of rectangular and circular glulam samples were computed from torsion tests and Saint‐Venant's isotropic torsion solution. The experimental results show that the depth‐to‐width ratios of the cross sections have no significant influence on the computed shear moduli of the glulam samples; thus, Saint‐Venant's torsion solution can accurately represent the linear torsional response of southern pine glulam beams.

Shear strength of spruce glued—laminated timber beams

The effect of size on longitudinal shear strength has been well established for Douglas-fir glued–laminated (glulam) timber beams. The present study examined whether this phenomenon exists in glulam beams made of spruce. The experiment consisted of three projects in which beams of various sizes were tested under concentrated mid-span load. The project A beams had clear spruce webs and white elm flanges with cross-sectional dimensions varying from 25 × 25 mm to 75 × 75 mm. The project B beams had spruce glulam webs with Douglas-fir flanges; cross sections ranged from 20 × 100 mm to 90 × 200 mm. In project C, three groups of 10 replications of commercially representative sizes of glulam beams were made from stiffness-rated spruce–pine–fir lumber. The beam cross sections were 76 × 200 mm, 76 × 400 mm, and 127 × 400 mm.The results indicated that depth, width, and shear plane had significant effects on the longitudinal shear strength of the beams in project A. Depth, width, and shear span of the small glulam beams in project B also had highly significant effects on shear strength. However, no effects of depth and width on the shear strength of glulam beams in project C were found. Regression analysis showed no dependence of shear strength on sheared volume for the beams of all three projects. The three-parameter Weibull model also failed to predict the near-minimum shear strength of spruce glulam beams. The results suggested that the lower-bound shear strength of spruce glulam beams is a constant (regardless of beam volume) and could be used as a single characteristic value for glulam design in shear. Further review of published data indicates that this may also be the case for Douglas-fir glulam but with a lower characteristic value than for spruce.