Glued Laminated Timber Beams Research Articles

Ductile Design of Glued-Laminated Timber Beams

Ductility is a fundamental component in the design of robust structures. For timber structures, the unfavorable material characteristics pose particular problems to its realization. Two approaches for improving the post-elastic behavior of glued-laminated timber beams have been investigated by testing and numerical analysis. The first is based on forming mixed beams with suitably assembled lamellae of different strength class; in the second, steel reinforcement is used. Satisfactory results have been obtained mixing laminations of different grade, whether from a single species or from different species, as long as the strengths of the lamellae are well differentiated. Steel-reinforced timber beams require taking special provisions in order to develop a ductile bending behavior, because material irregularities induce brittle failure of wood in tension before the steel bars may yield. Positive results were obtained, specifically preventing local failure modes, by releasing tension stresses in wood, by inser...

Experimental and analytical study of elasto-plastic bending behavior of glued-laminated timber beam with plural rib plates on tension side

Experimental and analytical study of elasto-plastic bending behavior of glued-laminated timber beam with plural rib plates on tension side

Shear behaviour of bond lines in glued laminated timber beams at high temperatures

A comprehensive research project has been carried out at the Swiss Federal Institute of Technology (ETH) on the fire behaviour of timber-concrete composite slabs (Frangi and Fontana 2000). The glued laminated timber beams used for the fire tests were bonded with a one-component polyurethane (1-K-PUR) adhesive. As one fire test on a slab showed an unexpected shear failure of a glued laminated timber beam, a series of tests was carried out to study the shear behaviour of different types of adhesives at high temperatures. The first part of the paper describes the results of the shear tests at elevated temperatures, in the second part the shear test results are compared to the fire test on a slab.

Modeling of Finger-Joint Failure in Glued-Laminated Timber Beams

This paper presents a novel approach to the modeling of failure of finger-joints in glued-laminated beams. A nonlinear strain-softening model with stochastic material parameters was used to characterize the failure zone of the finger-joint. Monte Carlo simulations of the behavior of laminations with finger-joints and of laminated beams were performed using the finite-element method. Various lamination thicknesses and beam depths were investigated, as well as the effect of varying the ductility of the finger-joint. Finally, the use of simplified finger-joint material models was also investigated. The results show that the proposed approach can account for such phenomena as the size effect and the laminating effect. Another observation is that the finger-joint ductility has a major influence on the lamination and beam strength, and that a special case of the present modeling approach can be made to coincide with the classic weakest link theory of Weibull.

Fire resistance of timber decking for heavy timber construction

The National Building Code of Canada provides both prescriptive specifications for timber beams and columns afforded equivalency to wood-frame construction with 45 min fire-resistance ratings, and simple calculation methods for determining fire-resistance ratings of larger glued-laminated timber beams and columns. However, the building code does not accept calculation methods for determining the fire endurance of mood decking materials. Although heavy timber roof construction is quite common in construction projects today, the use of heavy timber floor construction is not. The fire performance of floor and roof decking in heavy timber construction is, however, a critical concern in the renovation of older buildings. The authors receive more enquiries about the fire resistance of specific deck combinations, and how to increase the fire resistance of these building elements, than about any other fire-resistance related subject. The inability of the wood industry to respond to these enquiries with accurate information almost always results in costly wood solutions or the selection of non-wood alternatives for renovation projects. This paper addresses many of those questions.

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.

Shear Strength of Solid-Sawn Douglas-Fir Beams

The objective of this study was to improve current shear design criteria by establishing a test method for creating a database of beam shear strength of solid-sawn Douglas-fir lumber and correlating it to shear block test results; verifying whether the beam-size equation is a valid correlation between shear strength and beam size for solid-sawn material; and determining whether shear strength is more dependent on shear area, volume, or depth for modeling purposes. Experimental results are presented for 160 shear strength tests on unsplit, green, sawn No. 2 or better Douglas-fir lumber. Five different size specimens, ranging from 38 by 89 mm (2 by 4 in.) to 38 by 337 mm (4 by 14 in.), were tested in five-point beam shear. ASTM D143 shear block minors were cut and tested from each beam. Results adjusted to 12% moisture content were compared with prior research on southern pine and Douglas-fir glued-laminated timber beams. Statistical methods of censored statistics and regression investigated the following possible correlations: shear strength to beam size and beam shear strength to ASTM shear block strength. Results indicate that (1) a five-point test setup can consistently produce beam shear failures over a wide range of beam sizes; (2) shear strength is dependent on beam shear area; and (3) beam shear strength is related to ASTM D143 shear block strength values provided the reentrant corner stress-concentration effects are considered.

Delamination buckling of FRP layer in laminated wood beams

An analytical solution for predicting delamination buckling and growth of a thin fiber reinforced-plastic (FRP) layer in laminated wood beams under bending is presented. Based on a strength-of-materials approach, displacement functions for a delaminated beam under four-point bending are derived. Using force and displacement compatibility conditions, an explicit form relating the applied transverse load with the delamination buckling load is established. An explicit form of the strain-energy release rate is presented to study the delamination growth in beams under bending. The analytical solution is evaluated using experimental data for glued-laminated timber (glulam) beams reinforced with a thin fiber-reinforced plastic composite on the compression face. The delamination growth in bending is shown to behave differently to that of the in-plane loading case.

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.

Laminating Effects in Glued-Laminated Timber Beams

Existing lamination and beam test results were analytically reviewed to quantify the laminating effect for European and North American glued-laminated (glulam) timber. The laminating effect is defined as the increase in strength of lumber laminations when bonded in a glulam beam compared with their strength when tested by standard test procedures. Fundamental concepts are presented to define the laminating effect, estimates are made of its magnitude, and relationships are presented to describe its character. Our review of experimental data indicated that the laminating effect ranged from 1.06 to 1.59 for European glulam and from 0.95 to 2.51 for North American glulam.

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.

Effective Flange Width for Stress‐Laminated T‐System Timber Bridges

Stress-laminated T-system timber bridges consist of laminated deck sections combined with glued-laminated timber beams compressed transversely with high-strength steel bars. In the design of these structures, a deck-and-beam T-section is isolated and analysed as a T-beam. This paper presents a regression equation for the computation of effective flange width for stress-laminated T-system timber bridges; a width over which the normal stress can be assumed constant. Using actual dimensions, orthotropic material properties, and AASHTO truck loads, 125 bridge models were analyzed by a special finite element program for general anisotropic shell-and-beam-type structures. The results of the analysis were used to conduct a parametric study followed by a regression analysis to develop a prediction equation for the computation of effective flange width. Simplified equations for the computation of the effective width, which are within current upper and lower bound elasticity solutions, are proposed for use in design.

貫通仕口による木造ラーメン(大黒柱)構造の研究 : その2 実大試験体による加力テスト

This report is experimental research on the full size Nuki-structure under the lateral forces. These models are composed with a glued laminated timber beam and a glued laminated timbercolumn or a built-up glueded square-log column.

The performance of a ductile moment resisting connection between a precast concrete column and a timber beam

A ductile moment resisting joint suitable for the connection of a precast concrete column to a glued laminated timber beam is described. The design, fabrication and test performance of four variants of the joint which was fabricated from structural steel components are described in detail. The design was strongly constrained by practical considerations including the requirement that it be capable of attachment to both the beam and column at the time of erection, that wide construction tolerances be accommodated at the erection stage and that its fabrication could readily be undertaken by precast concrete and structural steel fabricators without special facilities. A capacity design approach for the joint was followed, based on the current New Zealand structural steel and structural concrete codes of practice. The design of the test joints was based on a defined strength hierarchy intended to result in large inelastic deformations being localised to the structural steelwork components. These components performed well in the tests. Some of the precast column sections tested were insufficiently reinforced for shear. Although confinement reinforcement was not provided for the purpose and it was not intended that they themselves be ductile, those precast concrete column sections with adequate shear reinforcement appeared to be capable of sustaining moment through a limited number of inelastic reverse cycle rotations even without confinement reinforcement. It appears that if such a joint is to be developed further, the inelastic rotational capacity, of the concrete column itself may more reliably provide the required ductility if confinement reinforcement is provided at the hinge position.

Strength and durability of hot-press glued-laminated timber beams

Hot-press glued-laminated timber was manufactured exclusively by one Canadian laminator between 1967 and 1970. Members made by this process have been found to be capable of seriously delaminating in service. The purpose of this study was to determine the strength and durability of lightly-delaminated hot-press beams. Eight such beams, plus two conventionally manufactured Glulam beams, provided material which was tested in either flexural-shear, flexural-tension-perpendicular-to-glueline after accelerated ageing, or vacuum-pressure cycling. For the accelerated ageing tests, material was subjected to either zero, one, two, four, six, or eight cycles of alternating high (85%) and low (35%) relative humidity at 50 °C, corresponding to equilibrium moisture contents of 16 and 6%, respectively. Flexural-shear strength of the hot-press material was somewhat lower than that expected of conventional material. Vacuum-pressure cycling of hot-press specimens resulted in delamination values exceeding the permissible amount. The average flexural-tensile strength of conventional material was substantially higher and less variable than that of hot-press material, both before and after accelerated ageing. Moreover, the flexural-tension-perpendicular-to-glueline tests after accelerated ageing cycles resulted in increased amounts of gluebond failure in the hot-press material. The results of the accelerated ageing and vacuum-pressure cycling tests indicate that even lightly-delaminated hot-press material has an inherent ability to delaminate and may perform poorly in situations of cyclic moisture environments.

S. Pine Beams from E-Rated and Proof Loaded Lumber

Prior publications have reported the development of an E -rating and tension proof loading method for selecting material for placement in glued-laminated timber beams. This method generally results in beams with higher stiffness and strength properties than beams fabricated from visually graded lumber. This paper report results of experiment duplicating that first southern pine experiment in every respect, except that the tension proof load of the critical tensile laminations constituted a fiber stress of 1.5 times the expected F b for the beams.

Tension Proof Loading for Southern Pine Beams

E-rating (measuring modulus of elasticity) and tension proof loading of lumber before laminating could improve stiffness characteristics and allowable design stresses for glued-laminated timber beams. Twenty-four large southern pine beams were fabricated from E-rated lumber — the high-E material located on the outside and low-E material in the core. Although average beam strength of southern pine equals Douglas fir, southern pine responds differently to tension proof loading than does Douglas fir. Southern pine may require higher proof loads (1.5 times beam F b ) than Douglas fir (1.3 times F b ) to eliminate brash pith-associated wood from the critical tension laminations. Since proof load breakage with southern pine was significantly less than with Douglas fir, a higher proof load stress for southern pine could be tolerated without causing excessive loss from breakage. Static beam modulus of elasticity is predictable from the E of the laminations with a correlation coefficient of 0.982.