There is a discrepancy between the estimated modulus of elasticity (MOE) of glulam based on the dynamic MOE of laminates and measured MOE. The discrepancy is greater for glulam manufactured with mixed species. This study was undertaken to reduce the discrepancy between those MOE values. The error rate of predicting MOE of glulam by the transformed section method, without considering tension and compression modulus differences, was about 30%. To estimate the MOE of glulam more accurately, the differences between compression and tension modulus should be taken into account in the transformed section method. The measured tensile and compressive strain at the center of glulam under a bending load showed the movement of neutral axis toward the tension side of glulam. Therefore, the compression and tension modulus differences for each species should be identified before estimating the MOE of glulam. The prediction of glulam MOE was improved significantly by reflecting the ratio of compression and tension modulus vs dynamic MOE of laminates. The outermost of laminates in the compression side under bending load experienced plastic behavior and failure. This caused the neutral axis to move to the tension side and increased tension stress to cause the glulam to fail abruptly in tension. To improve the bending performance of glulam, reinforcing compression laminates need to be considered.
International Conference on Contemporary Theory and Practice in Construction
Invention of cross-laminated timber (CLT) was a big milestone for building with wood. Due to novelty of CLT and timber’s complex mechanical behavior, the existing design codes cover only rectangular CLT panels, simply supported along 2 parallel or all 4 edges, making numerical methods necessary in other cases. This paper presents a practical engineering tool for stress and deflection prediction of CLT panels with non-classical boundary conditions, based on the software for the computational analysis of laminar composites, previously developed by the authors. Diagrams applicable in engineering practice are developed for some common cases. The presented methodology could be a basis for more detailed design handbooks and guidelines for various layouts of CLT panels and different types of loadings.
This paper deals with the behaviour of CLT composite T-beams composed of a Cross Laminated Timber (CLT) acting as panel attached to a Glulam (GL) girder. The paper investigates the effect of the configuration of the CLT panel and GL beam on the effective flange width of the CLT composite T-beams. When the CLT composite T-beams are...
High strength, low weight, corrosion resistance, and electromagnetic neutrality make fiber-reinforced plastic (FRP) a suitable candidate in many structural applications, including rehabilitation and strengthening as well as the development of new wood members. Advanced forms of reinforced wood construction can enable contemporary wood structures to play an even greater role in today's construction."In this work, the writers establish a novel technique for reinforcing wood members involving external bonding of pretensioned FRP sheets on their tension zones. An analytical model for the maximum initial pretension is verified with tests on carbon/epoxy-prestressed wood beams. Additional studies, both analytical and experimental of the flexural behavior of wood beams reinforced with prestressed carbon/epoxy FRP sheets demonstrate the superior performance of the hybrid system and emphasize its favorable strength, stiffness, and ductility characteristics. Finally, a methodology is described for the selection of composite material dimensions and initial prestressing to maximize structural performance.
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.
This report presents bending tests performed on composite beams made from glulam beams and cross laminated timber (CLT) panels. The composite beam, with a T-cross section, represents a section of a floor element in a multi-storey CLT construction system. The shear connections used were made either of doublesided punched metal plate fasteners, either of inclined screws, or of a combination of both fastener types. The screws are used to secure the shear connection with double-sided nail plates with respect to possible separation forces between the glulam and the CLT. An additional test with a screw glued connection was made for comparison as the upper bound case in terms of composite action. The results show the beams with double-sided nail plates (with or without screws) achieved a very high level of composite action and an overall satisfactory behaviour. Almost full composite action was achieved for the screw-glued composite beam. A detailed design example of the beam element according to the Eurocode 5 and Finnish National Annex is presented.
This paper describes an experimental test program and theoretical analysis which examines the reinforcing in flexure of glued laminated timber (glulam) beams using fiber reinforced polymer (FRP) and steel materials. A series of four-point bending tests were conducted till failure on both unreinforced and reinforced Douglas fir glulam beams in a simply-supported scheme. The focus of this research was to evaluate the effects of reinforcing materials, reinforcement ratio and arrangement on the flexural behavior. Test results showed that the flexural capacity, flexural global stiffness and timber tensile strain at failure were all improved considerably for reinforced timber beams when compared to the unreinforced control beams, in which the average improvement reached 56.3%, 27.5% and 49.4%, respectively. On the bases of the experimental results, a theoretical model was proposed to predict the flexural capacity and flexural stiffness of the reinforced timber beams. Most of the differences between theoretical and experimental results for both flexural capacity and flexural stiffness were within 10.0%, which showed a high accuracy of the proposed model. Subsequently a parametric analysis, which includes the axial stiffness ratio of reinforcement to timber, the relative location of tensile reinforcement, and the strength ratio of reinforced timber between flexural tension and compression, was undertaken to investigate the effects of the influential factors for both flexural capacity and flexural stiffness.
In this paper, results of flexure tests aimed at improving the structural behavior of softwood beams reinforced with unglued composite plates and at developing an effective alternative to the use of organic resins are presented. The addition of modest ratios of GFRP (Glass Fiber Reinforced Polymer) composite strengthening can prevent tension failure in timber beams. However the application of organic matrices presents problems of reversibility, compatibility and durability with timber and poor performance at high temperatures. The increment in capacity and stiffness and the analysis of the failure modes is the central focus of this paper. The experimental campaign is dealing with a significant number of un-reinforced and reinforced beams strengthened with unbonded GFRP plates. A 3-dimensional finite element model is also presented for simulating the non-linear behavior of GFRP-reinforced softwood beams. The ability of the numerical model to reproduce experimental results for the load–deflection curves is validated.