This paper presents the results of experimental research on full-size laminated veneer lumber (LVL) beams unreinforced and reinforced with CFRP sheets. The nominal dimensions of the tested beams were 45 mm × 200 mm × 3400 mm. The beams were reinforced using the so-called U-type reinforcement in three configurations, differing from each other in the thickness of the reinforcement and the side surface coverage. An epoxy resin adhesive was used to bond all the components together. A four-point static bending test was performed according to the guidelines in the relevant European standards. The effectiveness of the reinforcement increased with the level of coverage of the side surface and the level of reinforcement. The average increases of bending resistance were 42%, 51% and 58% for configurations B, C and D, respectively. The average value of bending stiffness increased for the beams of series B, C and D by 15%, 31% and 43%, respectively. Their failure mode changed from brittle fracture initiated in the tensile zone for unreinforced beams to more ductile fracture, initiated in the compression zone. The influence of the coverage of the side surface by the CFRP sheet and reinforcement ratio on the mechanism of failure and effectiveness of strengthening was studied in the article.
When glued-laminated timber are subjected to bending moment, they usually fail in a brittle way in the tension zone before the compressive zone reaches the compressive strength of wood. This means that the compression strength of wood is not fully exploited. By reinforcing the tension zone, the failure mode of glued-laminated timber can be changed from tensile to compressive. As a result, by utilizing the higher compressive strength, reinforced glued-laminated timber become stronger and the failure mode becomes compressive and ductile. This paper presents experimental results of the effect of steel reinforcements in the tension zone of glued-laminated timber. Four passively reinforced beams, four actively reinforced beams, and seven unreinforced beams were tested to failure in four-point bending tests. The experimental results confirmed the brittle tension failure in the unreinforced beams as well as the ductile and compressive failure in the reinforced beams. Furthermore, the experiments revealed the increase of the passively and the actively reinforced glued-laminated timber relative to the reference beams for strengths (26% and 39%) and stiffnesses (30% and 11%). Ductilities were increased from 7.7% for the reference beams to 90% and 75% for the passively and the actively reinforced glued-laminated timber, respectively.
Point-supported flat slabs made of cross laminated timber (CLT) for multi-storey buildings pose various challenges to structural timber design. One aspect are concentrated compressive loads, which cause stress concentrations in the form of shear and compression perpendicular to the grain at the point supports. The present work deals with this problem and shows a method, how the support area can be reinforced with a system connector. After a specification of the connector, the functionality of this construction element is described on the basis of experimental, numerical and analytical studies for a symmetrical loading. The interaction of the connector with the (CLT) is presented with an anlaytical model and numerical simulations, and evaluated with mechanical tests.
IOP Conference Series: Materials Science and Engineering
Summary
The timber bridge design although economical, often has difficulty producing enough rigidity so that a solution is needed to solve it. The use of CFRP (Carbon Fiber Reinforced Polymer) as a reinforcement of structural elements if properly designed and implemented can produce an effective and efficient composite structure. The experimental study aims to analyse the strength, stiffness and ductility of flexural strengthening composite bridge glued laminated timber beams-concrete plates using CFRP layers. The dimensions of the composite glued laminated timber beams 100/180 mm and concrete plate 75/300 mm with a length of 2,480 mm. The number of specimens is 3 composite glued laminated timber beams-concrete plate consisting of 1 test beam without CFRP reinforcement, 1 test beam with one layer CFRP reinforcement, and 1 test beam with three layer CFRP reinforcement. Experimental testing of flexural loads is done with two load points where each load is placed at 1/3 span length. The test results show that the strength of composite laminated timber beams glued - concrete plates BN; BL-1; BL-2 in a row 81.32; 82.82; 82.69 kN/mm; stiffness in a row 7.51; 8.22; 6.32 kN/mm and successive ductility of 16.67; 28.83; 20.21.
Wood is one of the most popular renewable natural materials. Nowadays, raw wood is hardly ever used in the construction industry. It has been substituted by glued laminated wood that is processed with the use of high-tech methods, thus eliminating the principal flaws and defects of the natural material. The deformability of glued laminated beams with combined reinforcement has been studied, under which the steel reinforcement of the periodic profile was placed in the dappings of the upper compressed zone, while ribbon-reinforced composite was glued to the bottom of the stretched zone. The graphical charts for the layer change of the deformations of wood, steel, and composite reinforcement from the beginning of the loading application to the moment of destruction are presented.
In this paper, an experimental research on bending behaviour of end-notched glulam beams and their bending behaviour after repairing with glass fibre reinforced polymer (GFRP) bars is presented. Altogether five glulam beams (100 x 220 x 4000 mm) made of spruce timber classified in the strength class C22 were tested. Experiment showed that originally, the beams failed in a brittle manner due to crack opening and its propagation. Cracks in the notch details were a result of excessive tensile stresses perpendicular to grain and shear stresses. Repairing the beams with GFRP bars after their failure completely restored and notably improved their load carrying capacity (average increase of 194%). Failure mechanism after repair changed from the original brittle tensile failure to more ductile failure in bending for most beams, proving the successfulness of the intervention. This study gives an insight in rehabilitation and repair possibilities of existing structures using advanced materials like GFRP bars.
The article presents the testing designating the impact of structural non-uniformity on the effectiveness of reinforcing bent wooden beams reinforced with basalt fibre (BFRP—Basalt Fibre Reinforced Polymers) rods. The obtained results demonstrate a positive impact of the strengthening in improving the bearing capacity and rigidness of the wooden beams. The article presents the impact of selected physical and chemical properties of wooden elements on the achieved strengthening reliability, increase in bearing capacity and the estimation of the reduction of deflections and stresses of bent beams, made from various wood quality classes and reinforced using BFRP rods. The conducted testing featured an analysis of the ability of using lower quality class lumber to strengthen the beams with pre-stressed basalt fibre rods. This solution allows for reducing the cross-section or lower the class of used wood with simultaneous maintenance of comparable rigidity and bending strength of beams, as in the non-strengthened beams.
A newly developed reinforcement system for glulam, actually representing a new generic wood com-pund, is presented. The composite consists on a hybrid cross-section, composed of intercalated layers of GLT and LVL, glued together along the width-direction of the beam. The specific build-up improves in first instance the mechanical properties of the glulam in the direction perpendicular to the grain significantly. Hence, the composite is especially well suited for the reinforcement of arrays of large holes in wide cross-sections. Secondly, the layers were tailored in such a manner, that the bending load capacity equalls that of the gross-cross-section. A parametric study was performed by means of the finite element method, to study the redistribution of stresses perpendicular to the main axis of the beam in the region of stress concentrations at one of the hole corners. Specifically, the load sharing of the vertical tensile force F_t,90 described in the German National Annex to EC5 was analyzed, and an analytical relationship depending on the thickness, elastic modulus and moment-to-shear-force ratio was developed.
Wood beam-column connections have traditionally been designed as simple shear connections, ignoring their potential moment capacity. A major reason for not utilizing such moment connections is linked to the brittle limit states that wood components exhibit. The purpose of this research was to develop and test a ductile and high-strength wood moment frame connection. A design procedure for such a connection is presented herein.
The proposed glulam beam-column connection utilizes an embedded steel knife plate with a reduced section that acts as a ductile yield link, thus limiting the moment that can be transferred through the connection. This configuration is intended to fail through yielding of the ductile link, thus preventing non-ductile failure mechanisms of wood from occurring. In addition, the connection provides more wood cover over the embedded steel plate, which potentially may increase the connection's fire rating as compared to typical connections.
Two specimens, based on a baseline connection developed using the design procedure presented, were monotonically loaded until failure. Unlike the first specimen, the second was reinforced in the perpendicular-to-grain direction using self-tapping screws. Failure mechanisms were analyzed, and performance characteristics related to the connection's strength, stiffness, and ductility were evaluated. Results indicated that the reinforced specimen exhibited higher strength, stiffness, and ductility compared to the unreinforced specimen. The reinforced specimen showed improvements of 9.49% and 42.2% in yielding and ultimate moment, respectively, compared to the unreinforced specimen. Moreover, an improvement of 31.3% in ductility was obtained using perpendicular-to-grain reinforcement.
International Conference on Architecture, Materials and Construction
Research Status
Complete
Summary
The current appeal for sustainable building materials has expanded the use of timber in construction. However, due to timber be a raw material, natural defects are present, what reduce its strength capacity and cause, in particular, brittle failures in the tensile region of timber beams. In order to increase the mechanical properties of these beams, fibre reinforcement can be applied. In this context, natural fibres, such as Sisal fibres, already used in various fields of construction, are an alternative for reinforcement of timber structural elements, by taking into account their adequate mechanical properties and, in special, for low-mechanical resistance wood species, such as Pinu sp, a species used widely in timber construction. This paper deals with an experimental analysis glued laminated timber beams (Glulam) of Pinus sp species, reinforced by Sisal fibres. Bending tests were performed on six beams with the following dimensions, 53 mm-width by 180 mm-height by 3000 mm-length, which were prepared with eight lamellas by 8 mmthickness. These beams were reinforced with Sisal strips that were glued by Epoxy adhesive on the bottom part of these beams. In addition, comparisons of result with nonreinforced Glulam were carried out. From the analyses of the experimental results, a decrease of 20 to 30% for the normal stresses, 5 to 10% for the shear stresses and 8 to 12 % for the displacements in relation to non-reinforced beams were verified.
