In the past study, we conducted compression tests with laminated veneer lumber of Japanese Larch. We observed the deflection and strain behaviour. As a result we could evaluate the bucking strength with Euler’s equation and Tetmajer’s method. For structural design we should expand the versatility of that method. Three wood species for structural members would be selected for these tests. Those were Japanese larch, Japanese cypress and Japanese cedar. For the test parameter, we set the 8types of slenderness ratio for the compression test and we conducted monotonic compression tests with pin-supported on both edges. For the mechanical properties we conducted compression tests with short column members and got yield compression for those materials. In the compression tests, we could see the bending deflection. We would get the ratio the maximum strength and yield strength for distinguish the limited slenderness ratio. As a result it was cleared that the limit slenderness ratio of these wood species was 100. And we could confirm that the Tetmajer’s method is useful for evaluation the yield strength.
In this paper, the linear buckling of a heterogeneous thick plate is studied using the Bending–Gradient theory which is an extension of the Reissner–Mindlin plate theory to the case of heterogeneous plates. Reference results are taken from a 3D numerical analysis using finite-elements and applied to Cross Laminated Timber panels which are thick and highly anisotropic laminates. First, it is shown that critical buckling loads are close to the material failure load which proves the necessity of a design model for the buckling of Cross Laminated Timber panels. Second, the soft simple support boundary condition is introduced as an opposition to the conventional hard simple support condition. It is shown that this distinction could be taken into account for designing timber structures depending on the accuracy needed. Third, it is observed that for varying plate geometries and arrangements, the Bending–Gradient theory predicts more precisely the critical load of CLT panels than classical lamination and first-order shear deformation theories. Finally, it is demonstrated that one of the suggested projections of the Bending–Gradient on a Reissner–Mindlin model gives very accurate results and could favorably allow the development of engineering recommendations for estimating properly transverse shear effects.
The force-displacement behaviour of structural timber members subjected to axial compression or combined axial compression and bending is distinctively non-linear. This behaviour is caused by the non-linear increase of the deformation due to the increasing eccentricity of the axial load as well as by the non-linear material behaviour of timber when subjected to compression. The present report describes experimental investigations on glued laminated timber members subjected to eccentric compression. The aim of these experimental investigations was to create a data base, which can be used to validate theoretical calculation models and to assess the accurateness of the design approaches given in the design codes for timber structures.
The specimens for the main bunch of experiments were produced using lamellas made of Norway spruce grown in Switzerland. For this purpose, a total of 336 lamellas were available. In the first step, non-destructive tests on the lamellas were performed. These tests aimed at the collection of data in order to characterise the raw material.
In the second step, the lamellas were strength graded. The aim of the grading process was to select two classes of lamellas for the production of the test specimens. The lamellas were selected so that they were suitable to produce glued laminated timber of strength classes GL24h and GL32h. Within the grading process, visual grading criteria as well as machine grading criteria were used.
In the third step, the graded lamellas were used to produce glued laminated timber members. Five tests series were produced. Each of the test series consisted of ten specimens. Three series were made of glued laminated timber GL24h and two series were made of glued laminated timber GL32h. The length of the timber members was varied between the different test series. The lengths were L = 1’400 mm, L = 2’300 mm and L = 3’200 mm respectively. During the production, the setup of the test specimens was recorded. Hence, the position and the orientation of every lamella within the test specimen were documented. Additionally, some non-destructive tests were performed using the test specimens.
In the last step, the glued laminated timber members were subjected to buckling tests. The test specimens were loaded with an eccentric compression force up to failure. During the tests, different measurements were carried out in order to document the experimental investigations as accurate as possible. Amongst others, the applied loads as well as horizontal and vertical deformations were recorded. For a subsample of 20 test specimens, additional local deformation measurements were performed using an optical measurement device.
In this paper, the linear buckling of Cross Laminated Timber walls is investigated. A 3D numerical study using finite-elements is presented for several Cross Laminated Timber geometries, ply configurations and boundary conditions. First, it is shown that critical buckling loads are close to the material failure load which proves the necessity of a design model for the buckling of Cross Laminated Timber panels. Second, through a comparison between soft simple support boundary conditions and conventional hard simple support conditions, it is shown that this distinction could be taken into account for designing timber structures depending on the accuracy needed. Third, several plate models, particularly the Bending-Gradient theory, are compared to these 3D reference results. It is observed that for varying plate geometries and arrangements, the Bending-Gradient theory predicts more precisely the critical load of CLT panels than classical lamination and first-order shear deformation theories. Finally, it is demonstrated that one of the suggested projections of the Bending-Gradient on a Reissner-Mindlin model gives very accurate results and could favorably allow the development of engineering recommendations to estimate properly transverse shear effects.
Project contact is Chris Pantelides at the University of Utah
A mass timber buckling-restrained braced frame is proposed to enhance the seismic resilience of mass timber buildings. Constructed using wood generated from the national forest system, the mass timber buckling-restrained brace will be integrated with a mass timber frame for structural energy dissipation under seismic or wind loads. The team will improve and optimize the design of structural components based on feedback from a real-time health monitoring system. Outcomes include guidelines for a lateral force resisting system of mass timber buildings in high seismic or wind regions.
The paper examines the behaviour of structural timber members subjected to axial compression or combined axial compression and bending. Based on experimental and numerical investigations, the accuracy of the existing approach in Eurocode 5 for the design of timber members subjected to axial compression or combined axial compression and bending is assessed and modifications are suggested. By means of extensive experimental investigations, a data base was created for the validation of calculation models and for the assessment of design concepts. In order to assess the behaviour of timber members subjected to axial compression or combined axial compression and bending, strain-based calculation models were developed.
The investigations indicate that the existing approach of Eurocode 5 based on 2nd order analysis can lead to an overestimation of the load-bearing capacity. Hence, a modified design approach was developed which agrees with the results of the Monte Carlo simulations very well and thus ensures a safe and economical design of timber members subjected to compression or combined compression and bending.
Buckling Restrained Brace Frames (BRBF) are a proven and reliable method to provide an efficient lateral force resisting system for new and existing structures in earthquake prone regions. The fuse-type elements in this system facilitate stable energy dissipation at large load deformation levels. Currently, the new trend towards mass timber vertical...
International Network on Timber Engineering Research
Buckling Restrained Brace Frames (BRBF) are a proven and reliable method to provide an efficient lateral force resisting system for new and existing structures in earthquake prone regions. The fuse-type elements in this system facilitate stable energy dissipation at large load deformation levels. Currently, the new trend towards mass timber vertical structures creates a need for a lightweight compatible lateral force resisting system. A Buckling Restrained Brace (BRB) component is possible to construct and feasible to implement when combining a steel core with a mass timber casing herein named the Timber-Buckling Restrained Brace (T-BRB). T-BRBs when combined with mass timber beam and column elements can create a system that will have advantages over the current steel framed BRBF system when considering recyclability, sustainability, framing compatibility, and performance. This paper presents findings on small scale testing of candidate engineered wood products for the T-BRB casing and testing of six full scale 12 ft long 60 kip braces according to code prescribed loading protocols and acceptance criteria.
Slender timber beams subjected to gravity loads may buckle in the out-of-plane direction. Normally, the same bracing system that is used to prevent lateral movements of the beams, caused by external transversal loading, also serve to increase the buckling strength of the beams. For the idealized case of a perfectly straight beam with full-bracing there is no force in the braces even at buckling because there is no displacement at the brace points. However, in real beams brace forces do develop during loading. This paper describes experimental and analytical studies performed on slender glulam beams subjected to gravity loads laterally stiffened by means of discrete bracing. In particular, the influence of relevant parameters such as i) brace stiffness, ii) brace position, iii) shape and magnitude of initial imperfections on the brace force were investigated.
The Japanese Building Code provides formulas to calculate the buckling strength for structural lumber and structural wooden engineered products such as glulam and LVL. The adaptability of these formulas against cross laminated timbers is discuss in this paper. To determining the buckling strength properties for cross laminated timbers a series of buckling test were operated for full-size cross laminated timber of certain structural grades. The buckling loads obtained though these tests were compared to those derived from the formulas given in the Japanese Building Code. The measured buckling loads and the calculated buckling loads were almost equivalent. The result indicated that in general the formulas given in the Japanese Building Code can well evaluate the buckling strength of cross laminated timbers.