Timber-concrete Composite Beams Research Articles

Flexural performance of full-scale two-span Nail-Laminated Timber Concrete composite slabs

This study examines the flexural performance of six 9-m full-scale two-span Nail-Laminated Timber Concrete (NLTC) composite slabs. The slabs were made with lumber beams edge-joined with double nailing, end-joined with butt joints, and the reinforced concrete topping connected with a set of notches, inclined screws, or a combination of both. The multi-span configuration of slabs reduces their deflections simply and effectively. Five-point monotonic bending tests were considered for all slabs. Before full-scale slabs, compressive and tensile pull-out tests of Timber-Concrete Composite (TCC) shear connections were performed, including notches and inclined screws. Tensile pull-out tests of shear connections were also included to emulate the negative bending moments that occur in the middle of the slabs. Failure modes, load–mid-span deflection relation, bending stiffness, and timber-concrete slip were evaluated for all slabs. A detailed 3D micro-Finite Element (FE) model of the shear connections was built in ANSYS software, whereas a macro-FE model of NLTC slabs was made in SAP2000, demonstrating a good fit for the timber-concrete interaction and the load-carrying capacity of the composite slab at the serviceability range. Moreover, an analytical elastic TCC beam with the Girhammar method was assessed and demonstrated as more precise than the traditional γ-method. Finally, an accurate prediction of the numerical and analytical (Girhammar) models for the bending stiffness at service loads up to 30% of capacity is observed, with errors in a range of 2–23% and 9–74%, respectively.

Experimental and theoretical evaluation of inclined screws in glued laminated bamboo and timber-concrete composite beams

In the timber-concrete composite beam, the timber beam in tension tends to fail in a brittle manner, which results in insufficient utilization of material strength in the compression zone and significant deformation problems. To improve the mechanical performance of the weak sections in the composite beam, a novel type of glued laminated bamboo and timber (GLBT)-concrete composite beam is proposed in which the bamboo layers are placed in the tension and compression zones of the beam. In this paper, thirty-six shear experiments were conducted to investigate the shear behavior of inclined screws in GLBT-concrete composite beams. The test results showed that the failure modes of diagonally positioned screws in GLBT-concrete composite beams involved pull-out failure of the screw and cone expulsion failure of the concrete. The pure tensile-shear loaded screws experienced the pull-out failure and single-hinge bending failure. For bamboo thicknesses of 30, 60, and 300 mm, the shear capacity of diagonally positioned screws increased by 27.9 %, 34.7 %, and 40.7 %, respectively, compared to the screws in pure wood members. Besides, the shear stiffness was improved by 40.4 %, 78.1 %, and 88.7 %, respectively. It was found that as bamboo thickness increased, the shear capacity and stiffness of diagonally positioned screws gradually improved, although the rate of increase gradually diminished. Among the four types of embedding methods, the ±45° diagonal screw connectors exhibited the highest shear stiffness, while the 135° unidirectional inclined screws (pure compressive-shear screws) had the lowest shear capacity and stiffness. This paper presented a theoretical model for estimating the shear capacity of inclined screw connectors in GLBT-concrete composite beams, which considered the various stress distributions of the screw connectors embedded in bamboo and timber layers.

Experimental investigation on adhesively bonded timber-self-compacting concrete composite beams with a thin slab

This study presents an experimental investigation of the failure characteristics, interface slip, strain distribution, and load-deflection response of adhesively bonded timber-concrete composite (TCC) beams fabricated using wet or dry processes. A total of six adhesively bonded TCC beams were produced with a span of 3.2 m and subjected to four-point bending tests. Wet and dry fabricated TCC beams revealed distinct failure modes. The results emphasized the critical role of bonding integrity in ensuring effective composite action and shared contribution mechanism. Wet-fabricated TCC beams exhibited a rigid bonding characterized by a consistent neutral axis alignment and load distribution along the beam span, while dry-fabricated beams experienced interface separation and compromised load-shared contribution, resulting in a significant reduction of the ultimate bending capacity of TCC beams. The outcomes showed that wet and dry TCC beams exhibited comparable load-to-mid-span deflection responses before failure, highlighting uniform behaviour and alignment with fully composite characteristics under the imposed loads. Furthermore, an analytical model for calculating TCC beams is presented and validated. The foundation of the analytical model is established upon the γ-method derived from Eurocode 5. The analytical model is compared with experimental results, highlighting its reliability and precision. Load-deflection responses, bending strain distributions, and ultimate failure loads are accurately captured, affirming the model's capability to anticipate the TCC beam behaviour.

Structural behavior of fully prefabricated glubam-concrete composite beams constructed of innovative connectors

This study focuses on developing fully prefabricated glued laminated bamboo (glubam)-concrete composite (BCC) beams constructed of the innovative ultra-high performance concrete (UHPC)-steel composite connectors. Five mid-scale prefabricated BCC beams with different connectors and concrete slabs were tested under short-term loading conditions to evaluate the flexural behavior. Particular emphasis was placed on verifying the convenience and deconstructablity of the proposed assembly structure through a secondary assembly and loading process, revealing that the prefabricated BCC has the advantage of rapid assembly construction and appreciable reusability. This assembly structure exhibits favorable bending performance under short-term loading conditions and it shows partial composite action. Reducing spacing and enhancing shear resistance of the UHPC-steel composite connector effectively improves the flexural behavior of BCC beams. In addition, casting a layer of laminated lightweight aggregate concrete with 30 mm thick on site can enhance the bending performance of the prefabricated BCC beam with effective control of the increase in its self-weight. Typical load capacity models derived from timber-concrete composite (TCC) beam were evaluated by the test results for predicting the load capacity of the prefabricated BCC structure. A comparison and evaluation were conducted on six large-scale BCC beams connected by different connectors, indicating that the proposed fully prefabricated BCC system possesses superior competitive advantages compared with existing BCC/TCC beams and it has a good application prospect in building engineering.

Experimental Analysis of Mechanical Behavior of Timber-Concrete Composite Beams with Different Connecting Systems

Timber-concrete composite structures are innovative structural systems which have become the subject of extensive research and practical usage, primarily due to their attractive mechanical properties. This article deals with the experimental procedure and the analysis of the mechanical behavior of two different series of timber-concrete composite beams with the same span and geometry of cross-sections. In the first BF-series, the screws were used as a connecting system between the timber and concrete parts, whereas in the BN-series the combination of notches and screws, as a more complex system, was used for the same purpose. Both series were exposed to loading up to a failure by means of the standard four-point bending test. The mechanical behavior of the BF and BN-series beams was analyzed by a comparative analysis referring to: the correlation of the failure loading and the deflection, mechanisms of failure, the strain development across the height of mid-span’s and support’s cross-sections, the horizontal displacement in the timber-concrete interlayer at the support zones, the value of shear stresses and the calculated values of the effective bending stiffness of the beams. The differences in bearing capacity between both series of beams were negligible (about 5%), the effective bending stiffness of BF beams is lower for 32.86% compared to the BN-series and the average value of deflections in BF-series beams is twice as high than in the BN-series. The BN-series beams showed better mechanical behavior in aspects of development of shear stresses in support zones, exhibiting lower shear stress values with an average of 40%.

Theoretical Analysis on Thermo-Mechanical Bending Behavior of Timber–Concrete Composite Beams

In this study, an analytical approach is introduced for predicting the bending behavior of a timber–concrete composite (TCC) beam subjected to a mechanical load and a non-uniform temperature field, in which the orthotropy of timber as well as interfacial slip are taken into consideration. The analytical model addresses the non-uniform temperature field using Fourier series expansion based on the heat transport theory. The stresses and displacements of the TCC beam under the thermo-mechanical condition are governed by the thermo-elasticity theory, and the corresponding solution is derived analytically by solving a group of non-homogeneous partial differential equations. The proposed solution is in good agreement with the finite element solution and exhibits higher accuracy compared to the Euler–Bernoulli beam solution that relies on the assumption of transverse shear deformation and isotropy. An extensive investigation is carried out to analyze how the bending behavior of TCC beams is influenced by variations in interfacial shear stiffness and temperature field.

Seismic Performance of Joint between Timber–Concrete Composite Beams and Steel Column with Innovative Semirigid Connections: Experimental and Numerical Studies under Quasi-Static Cyclic Loading Conditions

Seismic Performance of Joint between Timber–Concrete Composite Beams and Steel Column with Innovative Semirigid Connections: Experimental and Numerical Studies under Quasi-Static Cyclic Loading Conditions

Dynamic Properties of Timber–Concrete Composite Beams with Crossed Inclined Coach Screw Connections: Experimental and Theoretical Investigations

Due to the low density and stiffness of wood, traditional timber floor systems are prone to producing large vibration responses. By combining timber beams with concrete floors, timber–concrete composite (TCC) floor systems show stronger bearing capacity, higher bending stiffness, and better thermal and sound insulation behaviors when compared with traditional timber floor systems. In this study, the vibration performance of TCC beams with crossed inclined coach screw connectors was investigated using dynamic tests. The influence of the screw diameters and slab dimensions on the dynamic performance of the composite beams was evaluated. The test results demonstrated that TCC beams show good dynamic performance when used as a floor component and meet the preliminary requirements of floor vibration comfort for fundamental frequency. The fundamental frequency and damping ratio of TCC beams decreases with the increase in slab dimensions. The bending stiffness and natural frequency of TCC beams decrease smoothly when reducing the screw diameter from 16 to 12 mm. Additionally, two theoretical models were used to predict the natural frequencies of the TCC beams, and the predicted values show good consistency with the measured ones.

Flexural strengthening of timber-concrete composite beams using mechanically fastened and externally bonded combining mechanically fastened strengthening techniques

Timber-concrete composite (TCC) beams fail due to the tensile failure of the bottom timber lamellas, with the upper concrete remaining elastic, indicating a low utilization ratio of materials. Consequently, two types of strengthening techniques, namely mechanically fastened (MF) and externally bonded combining mechanically fastened (EB + MF), were used in this study to strengthen the TCC beams. Four-point bending tests were conducted to evaluate the strengthening efficiency of the MF and the EB + MF strengthening techniques for the TCC beams. Experimental variables include different strengthening techniques (MF, and EB + MF), types of reinforcement (steel and CFRP), and thickness of reinforcement. The test results indicate that the ultimate load capacity of the TCC beams was significantly improved, with a maximum improvement of up to 85.4% for the EB + MF and 30.6% for the MF strengthening techniques, respectively. The MF and the EB + MF strengthening techniques improved the bending stiffness of the TCC beams ranging from 10.8% to 41.6%. Generally, the MF strengthening technique shows a slightly lower strengthening efficiency in ultimate load capacity and bending stiffness compared with the EB + MF strengthening technique, respectively, indicating that the MF strengthening technique is also an effective way for strengthening the TCC beams. The comparison between the experimental and calculated bending stiffness indicates that the γ method reported in Eurocode 5 underestimates the bending stiffness by 40% on average for all the tested TCC beams.

The influence of notch connection location on the short-term behaviour of timber-concrete composite beams, modelling of TCC beams and research for optimal locations, a numerical study

Timber-concrete composite beams, known as TCC beams, have been widely used in rehabilitation or in new buildings where several types of connections are commonly inserted to ensure partial composite action between the timber joist and the concrete slab. The notched connections represent an effective system due to their strength and ductility and it is simple to cut from timber joists. As a result, a small number is needed for the composite beam to achieve high performance in terms of bending stiffness and load-carrying capacity. This paper aims to develop a FE model for TCC beams with notched connections. It considers realistic interactions between different components. The developed FE model can satisfactorily predict the full range load-mid-span deflection curves and the failure mechanisms. The predictions agree very well with the experimental results reported in the literature, including the stiffness and the load-carrying capacity. After the validation, a numeric study was established, it aimed to research the optimal location of a notch connection between different proposed locations, to figure out which place must be installed to ensure high performance of the TCC beams. As a result of this study, the notch installed at location P3000 was found to be the optimal location to assure the highest bending stiffness. While the maximum carrying capacity was achieved at location P3750.

Experimental and theoretical investigation on shear performances of glued-in perforated steel plate connections for prefabricated timber–concrete composite beams

Glued-in perforated steel plate (GIPSP) connections demonstrate significant shear strength and high slip modulus. Consequently, they indicate substantial potential for application in timber–concrete composite (TCC) structures according to the emerging tendencies in high-storey and large-span buildings. However, the application pattern in prefabricated TCC structures and the theoretical analysis of the shear performances of GIPSP connections are highly deficient. This hinders the application of this type of shear connection. In this study, the shear performances of GIPSP connections were evaluated using push-out tests. Ten groups of push-out specimens with different steel plate numbers, steel plate lengths, and concrete slab types were tested. The concrete slab types investigated in the experiments included a prefabricated concrete slab and cast-in-situ concrete slab. The experimental results were discussed in terms of the failure mode, load-carrying capacity, and slip modulus. The theoretical models for the load-carrying capacity related to the associate failure mode were discussed based on an analysis of the failure mechanisms. In addition, design proposals with regard to the load-carrying capacity and slip modulus of the GIPSP connection were presented. The research results can provide design guidance for TCC beams using GIPSP connections and prefabricated concrete slabs.

Application of external prestressing to timber-concrete composite beams

Timber-concrete composite beams are classified as modern constructions. They are created by connecting a timber and concrete element. They are designed in such a way that the concrete part of the beam is placed in the compressed zone, and the timber part is placed in the tension zone. Different types of fasteners can be used for connecting, from mechanical (screws, nails, perforated plates, parts of steel profiles, etc.) to chemical (various types of glues). In this work, the possibility of active strengthening for this type of beam by external prestressing, is examined. One way for applying an external prestressing force is shown. By experimental testing are determined results for prestressed and beam without prestressing. Obtained results are presented and compared.

Shear Behaviors of Steel-Plate Connections for Timber-Concrete Composite Beams with Prefabricated Concrete Slabs

To promote the development of timber-concrete composite (TCC) structures, it is necessary to propose the assembly-type connections with high assembly efficiency and shear performances. This article presented the experimental results of the innovative steel-plate connections for TCC beams using prefabricated concrete slabs. The steel-plate connections consisted of the screws and the steel-plates. The steel-plates were partly embedded in the concrete slabs. The concrete slabs and the timber beams were connected by screws through the steel-plates. The parameters researched in this article included screw number, angle steel as the reinforcement for anchoring, and shallow notches on the timber surface to restrict the slip of the steel-plates. Experimental results were discussed in terms of failure modes, ultimate bearing capacities, and slip moduli. It was found that increasing the number of screws could lead to the obvious improvement on the ultimate bearing capacities and the slip moduli at the ultimate state; and the angle steel as the reinforcement showed the slight influence on the ultimate bearing capacities and the slip moduli. The application of the shallow notch can greatly improve the ultimate bearing capacities and the slip moduli. The calculation models for the ultimate bearing capacities and the slip moduli of the steel-plate connections with and without shallow notches were proposed, which showed good accuracy compared with the experimental results.

Shear stiffness of notched connectors in glue laminated timber-concrete composite beams under fire conditions

Shear connectors ensure effective interaction between wood beams and concrete slabs of composite beams, and their properties noticeably affect the fire resistance of timber-concrete composite beams. To investigate the shear stiffness of notched connectors in glued laminated timber (GLT)-concrete composite beams under fire conditions, 16 shear tests were conducted. The effects of fire duration and notch length on shear properties of the connectors for a given spacing were studied. The fire tests indicated that the reduction of the notch length from 200 mm to 150 mm remarkably affected the failure mode of the shear specimens, changing from compression failure of notched wood to shear failure of notched concrete. The increase in fire duration reduced effective width of the notched wood, negatively affected the shear stiffness and shear capacity of the connectors, and the shear stiffness decreased more rapidly. The notch length did not have a substantial effect on the shear stiffness of connectors. Based on the experimental results, an analytical model to estimate the shear stiffness of notched connectors in GLT-concrete beam under fire conditions was established.

Effective width of timber-concrete composite beams with crossed inclined coach screw connections at the serviceability state

To support the design and application of timber-concrete composite (TCC) floor systems, the effective width of the TCC beams with crossed inclined coach screw connections at the serviceability state was evaluated in this study. The bending tests on the TCC beams with different slab widths were conducted to assess the shear lag effect in concrete slab and discuss the influence of slab width on the bending performance of TCC beams. A nonlinear finite element (FE) model for TCC beams was established in ABAQUS 6.14 and validated by the experimental results. Based on the experimental and FE studies, an extensive parametrical analysis was performed to evaluate the effect of various factors on the effective width of TCC beams. The presence of shear lag effect was proved by the experimental strain distributions in the concrete slab, and the shear lag effect was found more apparent for the tension strain at the bottom of concrete slab than the compression strain at the upper surface of slab. The FE numerical results showed high agreement with the test results in terms of the macro and micro bending performances of the TCC beams. In addition, the parametrical studies indicated that the effective width of TCC beams mainly depends on the load type, slab width-to-span ratio, slab thickness, and connection stiffness. Finally, for practical use, a general formula was proposed to calculate the effective width of the TCC beams.

Push-out tests on adhesively bonded perfobond shear connectors for timber-concrete composite beams

In this paper, perforated shear connectors (perfobond), used extensively in steel-concrete composite (SCC) beams, are implemented in timber-concrete composite beams (TCC) and experimentally investigated. In contrast to its original use, the perfobond connector is connected with an adhesive to the timber beam while welded in the SCC solution. On the concrete slab side, connection is achieved using the original concept, a combination of dowel action with bearing between concrete and connector. In this paper the mechanical behaviour of the shear connection using the perfobond connector in TCC beams is investigated by means of push-out tests. Concrete type, concrete strength and surface roughness of the connecter were the testing variables. The results are compared with the common shear connections for TCC in terms of strength, stiffness and ultimate slip. From this work, it can be concluded that perfobond connections give promising strength and stiffness results, however, for the geometries covered in the experimental program, the ultimate slip is limited. Nevertheless, the high stiffness and load capacity presented by this connection demonstrates a significant potential for its implementation in TCC, as high composite action can be achieved.

Push–out Test of Timber Concrete Composite Construction

In this study, push – out test specimen is proposed to explore the behavior of shear connectors in timber–concrete composite beams. Since there are no standard shapes and dimensions for determining the strength of connectors, push–out specimens such as those used for steel-concrete composite beams are suggested to study the behavior of connectors in timber concrete composite beams. Four specimens are tested. Two of these specimens are with one connector per side. The other two are with two connectors per side. The load and slip are recorded during testing. The results show that the ultimate load per connector ranges from 24.9 kN to 29.4 kN, with an average value of 26.9 kN. An equation is proposed to determine the ultimate load of the connector. Good agreement is achieved between the theoretical and experimental results. An average value of 0.98 is obtained for theoretical to experimental results.

Shear performance of assembled shear connectors for timber–concrete composite beams

This paper presents three types of assembled shear connectors consisting of a steel component anchored to timber by screws and glued-in rods (GiRs) for timber-concrete composite (TCC) beams. Single-shear tests were carried out to evaluate the shear performance of the proposed shear connectors. The test results showed that the anchors bent obviously and finally failed in “single-hinge” and “double-hinge” yield modes under lateral load. The timber surrounding the anchors was obviously crushed, and cracks in concrete were also observed during testing. The shear connectors with I-shaped steel anchored by GiRs exhibited the highest shear capacity of 158.92 kN. The folded steel plate shear connectors with GiRs and screws showed the highest slip modulus (38.41 kN/mm), and the highest ductility with an average coefficient of 29.6, respectively. In general, the shear connectors anchored with GiRs showed better shear performance compared to the screwed shear connectors. Finally, numerical simulation results indicated that the simulated load–slip curves were generally in good agreement with the test curves. The anchor diameter and strength and the frictional coefficient between anchors and the wall of the holes in timber have significantly influenced the shear performance of the proposed shear connectors.

Nonlinear finite element analysis on timber-concrete composite beams

To support the parametric analysis of timber-concrete composite (TCC) beams and the structural analysis of TCC frame systems, the computational effectiveness of various dimensional finite element (FE) models for TCC beams were evaluated in this study, including the one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D). It was found that the 1D frame FE model achieved by the fibre beam elements and the 2D model formed by the layered shell elements show apparently higher computational efficiency than the 3D FE model with solid elements. The FE models all exhibit good consistence with the test results in terms of the macroscopic bending performance of the TCC beams. Owe to the developing of the ABAQUS user subroutines in this study, the 3D model established in the ABAQUS/Explicit module could almost perfectly present the failure modes of the TCC beams, including the fracture of timber, failure of end connections, and cracks on concrete slab, and show higher accuracy of the numerical results than the 1D and 2D models. Additionally, the FE numerical interfacial strain and slip distributions are slightly larger than the test ones, due to various shortcomings of the definitions of the connections in the FE models. Generally, the FE models were validated to be feasible sufficiently for further studies on TCC structures.

Study on shear performance of notched connections for glulam-concrete composite beams under fire

Shear connection guarantees that the timber beam and concrete slab of a composite beam interact effectively. Shear connection performance markedly affects the fire resistance of timber-concrete composite beams. Shear connection experiments under fire are uncommon in comparison to those conducted at ambient temperature, and there have been few previous investigations on the shear performance of notched connections under fire. Six specimens were sheared at ambient temperature and ten specimens were sheared at elevated temperature in this study to determine the shear behavior of notched connections exposed to ISO fire. The length of the notch connection and the duration of fire exposure are two factors that may influence the shear behavior of the connections. With the increase of fire time, the shear bearing capacity and slip modulus of notched connections decreased. As notch length increased from 150 mm to 250 mm, the failure modes of shear specimens under fire changed from shear failure of concrete in the notch to compression failure of timber near the notch. Experimental results and finite element thermal analysis results were used to establish an analytical model for the shear bearing capacity of notched connections for glulam-concrete beams under ISO fire exposure.