Timber Beams Research Articles

Flexural strengthening of composite bridge glued laminated timber beams-concrete plate using CFRP layers

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.

Experimental Investigations of Timber Beams with Stop-Splayed Scarf Carpentry Joints.

The paper presents the results of an experimental investigation of stop-splayed scarf joints, which was carried out as part of a research programme at the Wroclaw University of Science and Technology. A brief description and the characteristics of scarf and splice joints appearing in historical buildings are provided, with special reference to stop-splayed scarf joints (so-called ‘Bolt of lightning’) which were widely used, for example, in Italian renaissance architecture. Analyses and studies of scarf and splice joints in bent elements presented in the literature are reviewed, along with selected examples of analyses and research on tensile joints. It is worth noting that the authors in practically all the cited literature draw attention to the need for further research in this area. Next, the results of the authors’ own research on beams with stop-splayed scarf joints, strengthened using various methods, e.g., by means of drawbolts (metal screws), steel clamps and steel clamps with wooden pegs, which were subjected to four-point bending tests are presented. Load-deflection plots were obtained for load-bearing to bending of each beam in relation to the load-bearing of a continuous reference beam. A comparative analysis of the results obtained for each beam series is presented, along with conclusions and directions for further research.

RESPONSE AND DAMAGE EVOLUTION OF SINGLE EDGE NOTCHED TIMBER BEAMS UNDER THREE-POINT BENDING

Two groups of small-size single edge notched beams (SENB) made of European spruce (Picea abies) were tested in three-point bending (3PB) until failure under displacement control. The first group comprised of eight solid and two glued laminated (GL) timber beams manufactured with (a) the single edge notch at the bottom of the mid-span and (b) the reduced ligament depth. The second group consisted of four GL timber beams with the single edge notch only. We employed digital image correlation (DIC) to quantify strains and displacements, capture the damage evolution, and track the sequence of failure patterns. In this work, we present response of the beams in terms of load vs. crosshead displacement of the moving crosshead and load vs. crack tip opening displacement (CTOD).

Behavior of masonry infilled Chuandou timber frames subjected to in-plane cyclic loading

The Chuandou timber frame is a traditional timber structural system widely used for nonengineered residential houses in southwestern China; this system is featured by beam-to-column joints with direct penetration tenons and free-standing column bases. As concluded by a previous study, the Chuandou timber frames with proper infills have exhibited better seismic performance than un-reinforced masonry structures in terms of collapse prevention, although the mortise-tenon connections, masonry infills, timber beams and columns may have sustained various extents of damage. To investigate the seismic behavior of the structural system, six full-scale Chuandou timber frame subassemblies were subjected to in-plane quasi-static loading, four of which were infilled with masonry walls. The test results show that the masonry infills provided the most lateral resistance of the system, whereas the timber frames could sustain a large lateral drift without losing their vertical stability. The observed failure modes were identified from different specimens. The lateral strengths of the specimens in the current test were evaluated using the existing code equations. The results suggest the necessity of considering the aspect ratio in calculating the shear strength of masonry walls.

Flexural behavior of timber beams strengthened with pultruded glass fiber reinforced polymer profiles

Timber is one of the materials widely used in construction and industry all over the world. In this paper, the behavior of strengthened timber beams made of beech wood (Fagus orientalis) were investigated experimentally. The composite timber beams were reinforced with flat, U-shaped, and L-shaped pultruded Glass Fiber Reinforced Polymer (GFRP) profiles. The GFRPs were attached to tensile or both tensile and compressive surfaces of beams. Altogether, 24 specimens, including 20 strengthened beams and 4 un-strengthened (control) beams, were tested under three-point bending test. Flexural behavior of specimens was evaluated through their load versus mid-span displacement curves, ultimate load carrying capacity, stiffness, displacement ductility, and capacity of energy absorption. The experimental results indicated that the mean value of modulus of rupture, flexural rigidity, ductility, and energy absorption of strengthened beams increased by up to 61, 59, 79, and 209% in comparison to control specimens, respectively. Finally, an analytical calculation has been conducted in order to predict the test data. There was a reasonable agreement between the test results and the results of numerical model.

Comparison and experimental verification of simplified one-dimensional linear elastic models of multilayer sandwich beams

Three analytical one-dimensional linear elastic models of composite laminated beams are considered – composite Bernoulli-Euler beam (BE), composite Timoshenko beam (T) and multilayer sandwich beam model (MS). They are compared with results obtained via finite element method for a two-dimensional model in plane stress state. Overall system stiffness is verified with experimental data obtained for two statical configurations – three-point bending and four-point bending. The first configuration concerned 8 types of three-panel cross-laminated timber (CLT) beams accounting for various materials and thickness of timber panels as well as various materials and thickness of adhesive layer, while the second one concerned 5 types of two-panel aluminium laminated beams accounting for different thickness of adhesive layer. Simplified multilayer sandwich model is found to be in good accordance with FEA results and with experimental data, while simple BE and T models are shown to provide erroneous estimates.

A Dynamic Bayesian Network framework for spatial deterioration modelling and reliability updating of timber structures subjected to decay

Reliability assessment of existing timber structures subjected to deterioration processes is an important task to evaluate their serviceability and safety levels. Towards this aim, data collected after inspection campaigns are often used for updating structural reliability and planning future maintenance/inspection activities. Under natural conditions, timber decay involves a large number of uncertainties related to material properties and environmental exposure. These uncertainties are also affected by temporal and spatial variability of associated deterioration processes. In this context, the main objective of this study is to propose a Dynamic Bayesian Network approach for updating the structural reliability of deteriorating timber structures using inspection data. The proposed approach can account for the uncertainties in the decay process and the effect of spatial variability. It is also useful for reliability updating considering the uncertainties of inspection techniques. The proposed methodology is illustrated with the reliability updating of a timber beam subjected to decay deterioration. Results indicate that this approach is useful for evaluating and updating of structural reliability from spatially distributed inspection data. Reliability updating could also be carried out from partial observations at given areas, which is very useful for large-scale infrastructure.

Constraining delamination of CFRP by beam corrugation

The reinforcement of timber and concrete load bearing beams is increasingly utilized. The most promising effect can be achieved by CFRP (carbon fibre reinforced polymer). However, the difference in mechanical properties of the materials used may be so vast that the two components slip from each other at high stresses. This study deals with the delamination of CFRP from a beam. Design of corrugated reinforced surface is presented. It is based on area enlargement, which leads to a higher applied force needed for CFRP delamination during 4-point bending. Moreover, the corrugated shape comes to synergy with the timber beam which deforms during the flexural load and cyclic humidity. Corrugated CFRP is able to adapt to transverse dimensional changes and vice-versa increases the bending stiffness in the longitudinal direction. All in all, the corrugated shape of CFRP constrains the delamination and seems to be applicable for long-term reinforcement.

Experimental and theoretical investigation on shear behaviour of small-scale timber beams strengthened with Fiber-Reinforced Polymer composites

This paper presents an experimental program conducted on small-scale timber beams strengthened with Fiber-Reinforced Polymer (FRP) shear reinforcement at shear spans to evaluate the strengthening efficiency of FRP shear reinforcement. The experimental variables involve FPR type, different layers, and attaching configurations. Tests results indicate that the Carbon-FRP (CFRP) shear reinforcement generally shows higher strengthening efficiency than Glass-FRP (GFRP) shear reinforcement. In particular, the shear capacity of the timber beams strengthened with longitudinally attached unidirectional CFRP can be improved by 32.9% for one-layer and 68.6% for two layers, respectively. Transversally attached unidirectional FRP reinforcement at the shear spans of timber beams contributes insignificant increase of shear capacity. The bidirectionally weaving GFRP provides the strengthened timber beams with a limited increase of shear capacity compared to the bidirectionally attaching unidirectional GFRP. Finally, an analytical solution is driven for predicting the shear capacity of the FRP strengthened timber beams. It is shown that the calculated values are in good agreement with the experimental results indicating the theoretical derivations can be used to predict the shear capacity of the timber beams strengthened with FRP shear reinforcement effectively.

Internal GFRP Reinforcement of Low-Grade Maritime Pine Duo Timber Beams.

This paper presented an experimental structural-scale test campaign used to analyze the flexural behavior of low-grade maritime pine (Pinus pinaster Ait.) duo timber beams reinforced with an internal glass fiber-reinforced polymer (GFRP) sheet. For this purpose, thirty (30) unreinforced duo beams and thirty (30) duo beams internally reinforced with a unidirectional GFRP sheet with an areal mass of 1200 g/m2 were produced and tested. The addition of a low GFRP reinforcement ratio (1.07%) in the tension zone of the duo beams provided an average improvement of 8.37% in bending stiffness (EI) and an increase of up to 18.45% in ultimate moment capacity. In addition to this improved bending behavior, the internal GFRP reinforcements seemed to decrease the influence of wood singularities and wood heterogeneity on mechanical properties, which allowed for better characteristic values to be reached and for the achievement of results with less variability.

Behavior of Timber Beams Strengthened by Jute Fibers

The study involves strengthening timber beams by known jute fibers with various forms of strengthening and comparison the bending test results with the control beams and beams strengthened by steel plates. Twenty-two timber specimens with dimensions (70×100×1000) mm are divided into eight groups and loaded under a one-point load. The work is carried out to study the flexural and shear strengthening effects on behavior of the tested beams. Four specimens wrapped in U technique in single and double layers, along the whole length of the beam in full and strips wrapping technique, seven beams bonded in full and spiral configuration, seven timber specimens wrapped in flexural strengthening technique with single and multiple layers, and two samples strengthened by steel plates. The results show that jute fibers strengthening are improved the ultimate loads of timber beams by between (30%-101%) compared with the control beams for different types of strengthening and by about (80%, 85%) using steel plates strengthening. On the other hand, the mid-span deflection are decreased by between (28%-45%) at the same load. Furthermore, it is found that the highest ultimate load deflection is when the beam wrapped in full strengthening technique. The ductility, stiffness, toughness at yield load and toughness at ultimate load are increased by between (21%-51%), (10%- 73%), (45%-373%), and (57%-401%), respectively. The jute fibers strengthening have high elasticity performance and prove that the jute fibers materials have a large potential to act as a structural strengthening material.

Behaviour of Post-Tensioned Kempas Timber Beam with Two Tendon Types

The post-tensioning technology is commonly used for concrete structures especially bridges. This technology is applied for timber elements in many countries effectively. In Malaysia the timber post-tensioning still not known yet. This research aim to propose the post- tensioning technique for timber beams. The timber type is Malaysian Kempas and the device used to apply the post-tensioning force is hydraulic jack. Three types of specimens were tested using the bending test (four-point bending test) for a simple support beam. two type of specimens are post-tensioned timber beams with black threaded rod bar (PTBR) and post-tensioned timber beams with silver threaded rod bar (PTSR). All the specimens’ length is 1.2meter and the dimension of timber is 90mm x 40mm. The increment of moment capacity of post-tension timber beam compared to the timber beam the moment resistance increment is 1.42 times. The moment resistance of the post-tensioned timber beam had average increment is 27.4% - 31.8%. The other finding is the failure mode of specimens it is changed from brittle tension failure to ductile failure (compression failure) the cause of this behavior is the role of the post-tensioning rods.

Vibration Behaviour of Natural Timber and Timber Concrete Composite Deck System

Timber–Concrete Composite (TCC) structure consists of timber joists or beams effectively interconnected to a concrete slab cast on top of the timber members. This type of structures has applications in multi-storey buildings and short-span bridges particularly in developed countries such as America, Canada, Australia and New Zealand. In Malaysia, these timber concrete composite (TCC) fields are extremely uncommon compared to European country. This paper is investigated the TCC deck system as a new slab structure element that could be used in Malaysia. The use of TCC deck system with Malaysian Kempas timber and normal weight concrete is advantageous in providing a lighter structure, more sustainable and possibly a smaller foundation. Therefore the main objective of this research is to study the vibration behavior of kempas timber (natural timber) in timber deck and TCC deck by experimental modal testing. The vibration data results were conducted by modal experimental test. Then the model is verified by finite element using SAP 2000 software. The connector type that used is screw in TCC deck. The size of each deck is 3.6m x 0.8m, the thickness of concrete is 65mm and the timber beam unit with dimension 3.6 x 0.09x0.04 m. The specimens of timber and TCC deck were tested using an electrodynamic shaker. The data were analyzed using ME Scope software to determine the natural frequency and mode shape of the timber and TCC deck system. The modal experimental results for all tests were more than 8 Hz, it accepted since the vibration limitation for timber floor is 8 Hz. The TCC deck frequency due to shaker excitation is higher than only timber deck which means that the TCC improve vibration resistance property compared with only timber deck vibration resistance.

EXPERIMENTAL INVESTIGATION OF LOAD-BEARING CAPACITY AND DEFLECTIONS OF FULL-SCALE GLUED LAMINATED TIMBER BEAMS

With the transition to the design of timber structures in accordance with European standards, problems arise in assessment of the load-bearing capacity of glued timber structures that are caused by insufficient amount of data about the physical, mechanical and deformation properties of glued timber, which is produced in Ukraine. The aim of the work was to determine the load bearing capacity in bending and deflection of a glued timber beam under the action of a concentrated load in the middle of the span. Two glued laminated timber beams were used in the experiment. Both beams were made using lumber from pine wood and a moisture-curing onecomponent polyurethane adhesive Kleiberit PUR 510 FiberBond. The beams have the dimensions of the cross-section: width of 120 mm and height of 180 mm. The length of the beams was 9880 mm. Each beam consisted of 9 layers of 20 mm thick lamellas glued together. Considering the absence of the data on the strength class of the beam material, the theoretical load bearing capacity and deflection were determined according to the characteristics of the GL24h class (minimum strength class), and amounted to 722 kgf and 19.1 cm, respectively. As a result of the tests, the failure load and the deflection of the beams were determined, and the dependences of the deflection on the load were obtained. The actual deflection of the beams determined was 251 mm and 275 mm, which is 1.31 and 1.44 times higher than the predicted deflection. Accordingly, the failure load determined experimentally is 1.96 and 2.03 times higher than the theoretical value. During the tests, the features of the deformation and the nature of the destruction of the beams were investigated. Wherein, the determining factor was the presence of defects in timber and lamellas joints along the length in the most stressed layers. Based on the data obtained, recommendations on manufacturing aimed at the increasing the bending strength of glued laminated timber beams are given. The results obtained will be further used in the development of structural solutions for hybrid timber-concrete floors.

STUDY ON STRENGTH OF GLUED LAMINATED TIMBER BEAMS WITH ROUND HOLES

STUDY ON STRENGTH OF GLUED LAMINATED TIMBER BEAMS WITH ROUND HOLES

Deflection estimation of glued laminated timber beams reinforced with CFRP fibre composites

Deflection estimation of glued laminated timber beams reinforced with CFRP fibre composites

Dynamic effects in reinforced beams at brittle failure – evaluated for timber members

Brittle failure in reinforced beams results in associated stress release in the beam. The reinforcement is activated to carry the released stresses by deformations between the beam and the reinforcement. This sudden process leads to dynamic impact, resulting in additional stresses in the system. In this paper, an analytical engineering approach is presented to estimate the magnitude of the corresponding stresses. The magnitude is dependent on the stiffness ratio between the reinforcement and the reinforced element failing in a brittle manner. On the example of timber beams with shear reinforcement in form of screws or threaded steel rods it is shown that a small increase in plastic deformation capacity of the reinforcement helps to considerably reduce the stress increase due to dynamic impact.

Experimental and numerical investigations on timber-concrete connections with inclined screws

In new and existing buildings, it is important that floors are sufficiently strong and stiff in plane. In comparison with pure timber floor systems, timber–concrete composite structures are often used as floor solutions to better combine acoustic separation with both greater load-carrying capacity and increased stiffness, also resulting in significant improvement of the serviceability vibrational comfort. The choice of a structurally effective yet inexpensive shear connection between the concrete topping and the timber joist is crucial to make the composite floor a viable solution that can compete with reinforced concrete and steel floors. The use of inclined screws to connect the timber beam to the concrete topping represents a possible solution to maximize the slip modulus of the connection and, at the same time, to keep the construction cost within acceptable values. In this paper, the mechanical behavior of such a type of timber to concrete connection is explored via experimental pushout tests and numerical investigations. The specimens tested were made of an inner timber block connected to two outer concrete slabs by means of two 8 mm diameter screws per side. To reproduce the timber flooring used in real practice as permanent formwork for the placement of the concrete topping, an OSB layer was introduced between the timber block and the concrete slabs of the specimens. Experimental results were statistically assessed to compute the mean slip moduli and the characteristic values of the shear strength. A mathematical model of an inclined elastic beam on an elastic foundation capable to provide the slip modulus of the system was developed. The dependency of the slip modulus upon the screw inclination and the interlayer flooring thickness was also investigated. The accuracy of the theoretical results was assessed through comparisons with experimental results.

The multilayered soil-structure seismic interaction and structure vibration mechanism

The morphology of subsoil influences to soil-structure interaction and it makes complex to predict seismic structural stability. The structural elements seismic response associate to soil-structure interaction is required expansive investigation with considering soil morphology. The main objective of the present study is to identify influence of near-fault ground motion mechanism reach to the structure element for evaluate strain energy modification due to the morphology of subsoil and developing load and displacement on the structural element with built-up synthetic subsoil for soil-structure seismic interaction design. The results of the numerical simulation revealed that the (i) displacement mechanism and applied seismic load of the structural element, (ii) strain energy modification and (iii) the structural vibration patterns of continuous beam in a timber frame have been changed in associated to the soil foundation characteristics. The innovation of this study is the soil-structure interaction, the soil layers interaction, near-fault ground motion and mechanical properties of the soil at different location of the soil foundation are fundamental parameters to control continuous timber beam seismic design.

Experimental and theoretical investigation of prefabricated timber-concrete composite beams with and without prestress

This paper presents a summary of the experimental programmes and theoretical analysis of the bending performance of non-prestressed and prestressed timber-concrete composite (TCC) beams. Two non-prestressed and three prestressed composite beams were selected, and their flexural behaviour was evaluated. Three types of ductile fabricated connections were applied to the prestressed composite beams, whereas two types were applied to the non-prestressed beams. The concrete slabs with embedded steel plates and timber beams were connected together using coach screws. On the surfaces of the embedded steel plates, the portions in contact with the wooden beam were interspaced with a vulcanized rubber layer to improve the mechanical performance of shear connections and composite beams. A series of four-point bending experiments were performed until collapse failure occurred in a simply-supported scheme. The test results demonstrated that the TCC beams using steel plate + screw connections exhibited excellent structural performance. The flexural capacity of the prestressed specimens was improved by approximately 110% compared with the non-prestressed specimens. Due to the addition of the rubber layer in the TCC connections, the flexural capacity of the prestressed composite beams was improved by 25.2%. Based on the ‘γ–method’, a theoretical analysis was proposed for calculating the flexural capacity and bending stiffness for both non-prestressed and prestressed TCC beams. The theoretical results showed good agreement with the experimental evidence.