Timber-concrete Composite Systems Research Articles

Experimental evaluation and theoretical modeling of eco-friendly bamboo scrimber-UHPC members with enhanced shear connectors

Timber-Concrete Composite (TCC) systems are applied widely in bridges and buildings. This study innovatively combines the eco-friendly attributes of Bamboo scrimber with Ultra-High Performance Concrete (UHPC) to develop TCC systems, leading to the formulation of Bamboo scrimber-UHPC (BS-UHPC) composites. These composites are designed to boost both mechanical behaviors and environmental sustainability. The research conducts an extensive analysis through eight series of push-out tests on BS-UHPC systems, employing diverse shear connectors such as notches, inclined bolts, and stencils. It provides an in-depth examination of the failure mechanisms, detailing general load-slip behaviors and analyzing the progression of failure. The findings reveal the influence mechanism of UHPC and shear connectors on the mechanical properties and failure modes of these composites, with notched shear connectors demonstrating the highest shear capacity with 134 kN. Additionally, the study explores the efficacy of notch connections through finite element models for parametric analysis, enabling a quantitative assessment of concrete cracking areas. Building upon these insights, the research proposes and validates theoretical models for predicting the shear capacity of these composites. Moreover, this paper employs life-cycle assessment to evaluate the environmental impact, specifically CO2 emissions of the BS-UHPC composites within service life, comparing them with those of traditional timber-ordinary concrete and steel-ordinary concrete systems. The results indicate that BS-UHPC composites offer significant improvements in mechanical behaviors while also achieving the lowest CO2 emissions with 78 kg CO2-Eq/m3 among the materials tested. This positions BS-UHPC composites as an advantageous choice for practical engineering applications.

Current practice and recent developments of shear connectors for timber concrete composite applications: A state of the art review

Several studies have been made on timber concrete composite shear connectors and most of these connectors are brittle at failure. Ductile shear connectors are not studied as extensively as ordinary shear connectors and the interest to study high ductility shear connectors increased in the past two decades. Recent literature references were chosen and reviewed on construction techniques of timber concrete composite shear connectors. A detailed summary of timber concrete composites, the mechanical properties of connectors, and types of connection systems are presented. Experimentally validated design guides available for timber concrete composite systems are presented and the potential for the development of new simplified connectors is discussed. Finally, recent applications of timber concrete composite connectors and possible areas of future research regarding the development of high ductility and energy dissipation capacity shear connectors are stated.

Construction System for Rural Tourism Facilities in the Eastern Black Sea Region: Timber–Concrete Composite System with Artificial Notches

Construction System for Rural Tourism Facilities in the Eastern Black Sea Region: Timber–Concrete Composite System with Artificial Notches

Reinforced cross-laminated timber-concrete composite floor systems

This paper presents full-scale experimental investigations on cross-laminated timber concrete composite (TCC) systems. The primary objective was to determine the stiffness, ultimate load-carrying capacity, and failure modes of TCC systems using three different shear connectors: self-tapping screws, steel kerf plates, and proprietary glued-in perforated steel plates. The secondary objective was to determine the effectiveness of shear reinforcement in the CLT panels. The TCC system was comprised of 245 mm thick, 7-ply CLT panels with a 150 mm concrete topping. A total of 24 half-span (4.6 m long) and 9 full-span (9.2 m long) CLT and TCC floor segments were tested under symmetric four-point bending as well as torsional bending. For all test series, the CLT panels were either unreinforced, or reinforced using self-tapping screws. The shear reinforcement increased rolling shear capacity which helped to avoid CLT shear failure. Adding the concrete topping increased the shear capacity by up to 167%. The tests showed that the floors with steel kerf plates exhibited the highest capacity and stiffness, while also being the most easy-to-install solution. The results from this research guided project-specific design decisions for “Limberlost Place”, a mass timber building for George Brown College, in Toronto, Canada.

Flexural behaviour of a new timber-concrete composite structural flooring system. Full scale testing

Timber-concrete composite systems are a high-performance alternative for building floors, of great interest in the current context of environmental concerns. Looking for a more eco-friendly solution, the paper presents a new flooring system with a wood-concrete connection that does not require adhesives or special metal elements. Four-point bending tests were performed on TCC flooring samples with a span of 6.0, 7.2 and 8.4 m. Its cross section was a prefabricated piece in the shape of an inverted T made up of a lower glulam flange, glued together with a central plywood rib with aligned holes in its upper part that go through the entire thickness of the plywood. The set was completed with a top layer of poured-in-place concrete. The connection between both materials is achieved by penetrating the concrete into the rib holes. Additionally, corrugated steel bars were placed through said holes to achieve ductile behaviour. In all cases, a slenderness ratio of L/24 was used. The experimental results showed that the lowest value of ultimate load obtained was 4.3 times higher than the total service load estimated for a building for public use (9 kN/m2). The maximum deflection of the total load was between L/573 and L/709 for the loads corresponding to a building for public use (9 kN/m2) and between L/1069 and L/1340 for the case of residential type building (5 kN/m2). An analysis of the effects of vibrations in the service limit state in relation to user comfort has been included. The results indicate that the system satisfies the requirements for the intended uses.Consequently, the proposed solution shows its effectiveness both in terms of strength and stiffness for the construction of light floors, being easy to build and having high performance.

Analytical Procedure for Timber−Concrete Composite (TCC) System with Mechanical Connectors

In the construction of modern multi-storey mass timber structures, a composite floor system commonly specified by structural engineers is the timber–concrete composite (TCC) system, where a mass timber beam or mass timber panel (MTP) is connected to a concrete slab with mechanical connectors. The design of TCC floor systems has not been addressed in timber design standards due to a lack of suitable analytical models for predicting the serviceability and safety performance of these systems. Moreover, the interlayer connection properties have a large influence on the structural performance of a TCC system. These connection properties are often generated by testing. In this paper, an analytical approach for designing a TCC floor system is proposed that incorporates connection models to predict connection properties from basic connection component properties such as embedment and withdrawal strength/stiffness of the connector, thereby circumventing the need to perform connection tests. The analytical approach leads to the calculation of effective bending stiffness, forces in the connectors, and extreme stresses in concrete and timber of the TCC system, and can be used in design to evaluate allowable floor spans under specific design loads and criteria. An extensive parametric analysis was also conducted following the analytical procedure to investigate the TCC connection and system behaviour. It was observed that the screw spacing and timber thickness remain the most important parameters which significantly influence the TCC system behaviour.

Hysteretic performance of angle steel connections in a timber-concrete composite system

Timber–concrete composite systems are widely used in Europe, North America, and Australasia, primarily due to their good mechanical performance in terms of statics, dynamics, and seismic response. In addition, the concrete slab provides excellent protection to the timber, making such systems suitable for outdoor application. The seismic performance of timber–concrete composites is normally governed by their ductility and energy dissipation capacity. However, few design codes address the ductility and energy dissipation capacity of timber–concrete composite systems, owing to a lack of reliable performance data. Therefore, further research on the hysteretic performance of timber–concrete composite systems is necessary. In this study, six timber–concrete composite specimens with an angle steel connection of the same size were investigated using reversed cyclic tests. The corresponding failure modes were observed, and the salient features of the connection, i.e., the stiffness, ductility, and energy dissipation, were computed from the test results. The force mechanism of the timber–concrete composite specimens under reversed cyclic load was analyzed. Equations were presented to calculate the yield force and negative force in the same load step. A comparison of the test results and the theoretical results indicated good agreement.

CLT concrete composite floors with steel kerf plate connectors

This paper presents experimental investigations on timber-concrete-composite (TCC) floors with transversely installed steel kerf plates as shear connectors. The TCC system was comprised of 245 mm thick, 7-ply cross-laminated timber (CLT) panels with 150 mm concrete topping. Three embedment depths of the steel kerf plates in CLT (35 mm, 70 mm, and 90 mm) were evaluated at hand of 18 small-scale shear tests. It was shown to be beneficial to only engage the top layer of the CLT panel in order to avoid rolling shear failure. Subsequently, two full-scale TCC floor segments were tested under symmetric four-point bending. The tests confirmed that the TCC floors with steel kerf plates can be designed using the established gamma procedure, and that they exhibited adequate capacity and stiffness to provide an economical solution. The results from this research were utilized to make project-specific design decisions for “The Arbour”, a 10-storey mass timber building for George Brown College, located in Toronto, Canada.

TIMBER-CONCRETE COMPOSITE-A HIGH-EFFICIENT AND SUSTAINABLE CONSTRUCTION METHOD

Timber-concrete composite (TCC) is a well-tried building method for construction of sustainable and robust floor systems with high load-bearing capacity. TCC sections consist of timber beams linked by shear connectors with a plain or reinforced concrete slab. Usually, by the shear connectors only flexible bond between the timber beams and the concrete slab may be provided. Nevertheless, TCC slabs have high flexural stiffness and appropriate load-bearing capacity enabling their application in residential and office buildings, and even in bridge construction. The paper reports state-of-the-art and recent developments in design and construction of TCC slabs. Especially, in the context of revaluation and strengthening of existing timber-beam ceilings it is a widely accepted technique today. But also, in design of new buildings, TCC slabs are an advantageous solution because of their reduced environmental impact in contrast to traditional reinforced concrete slabs. By many examples in recent design practice the high efficiency of TCC systems was proved.

Sustainability Design Considerations for Timber-Concrete Composite Floor Systems

Over the last few decades, there has been growing interest in the use of low-carbon materials to reduce the environmental impacts of the construction industry. The advent of mass timber panels (MTP), such as cross laminated timber (CLT), has allowed structural engineers to specify a low-carbon material for a variety of floor design considerations. However, serviceability issues such as vibration and deflection are limiting the construction of longer span timber-only floor systems and have encouraged the development of timber-concrete composite (TCC) systems. The use of concrete would negatively impact on the carbon footprint of the TCC floor system and should be minimized. The purpose of this study was to study the impact on embodied carbon in the TCC system, when the ratio of timber and concrete was varied for specific floor spans. Two MTP products were considered, CLT and glued laminated timber (GLT). The floors were designed to satisfy structural, acoustic, and vibration criteria, and the results were presented in the form of span tables. It was found that using thicker MTP instead of adding concrete thickness to meet a specific span requirement can lead to lower embodied carbon values. Increasing concrete thickness for long-span floor systems led to a reduction in allowable floor span due to the vibration criterion being the controlling design parameter. Increasing timber thickness also resulted in higher strength and stiffness to weight ratios, which would contribute toward reducing the size of lateral load resisting systems and foundations, resulting in further reductions in the embodied carbon of the entire structure.

Modelling short-term monotonic response of timber–concrete composite structures

Timber–concrete composite is an efficient hybrid construction material that exploits the advantageous properties of timber and concrete. The use of shear connectors enables the two dissimilar materials to act together, resulting in an increase in global stiffness as well as load-carrying capacity. As this composite material is becoming increasingly more popular in the construction industry, there is a need to develop analysis tools that have general applicability to timber–concrete composite systems with variations in loading schemes, specimen configurations, materials, and types of shear connectors. One such tool, a generic two-dimensional nonlinear finite element model, is proposed in this paper; it is verified through numerical simulations of six experiment series carried out by other researchers. Good agreement between experimentally observed behaviour and numerical simulations was generally obtained.

Evaluation of composite action in cross laminated timber-concrete composite beams with CFRP reinforcing bar and plate connectors using Digital Image Correlation (DIC)

This research proposes new types of shear connectors made of carbon fibre reinforced polymer (CFRP) composites for effective stress transfer between the timber and concrete sections in cross laminated timber (CLT)-concrete composite beams. New shear connectors are designed and made of bidirectional carbon fibre reinforced polymer (CFRP) composite plates and crossed CFRP reinforcing bars. The mechanical performance, bending stiffness, ductility, and interfacial slippage and strain of timber-concrete composite (TCC) beams with CFRP connectors are compared with those with steel plate and screw systems through four-point flexure testing. Local slip, interfacial slip and strain behaviour are comparatively analysed for connections with equivalent axial stiffness using a Digital Image Correlation (DIC) based technique, so that relative composite behaviour could be determined. Furthermore, a cost evaluation is undertaken to compare the feasibility of proposed shear connectors for construction of TCC systems. Results from flexural tests demonstrate that CFRP rod specimens experience higher ultimate load and bending stiffness in elastic loading stage and ductility in failure while slippage at serviceability and ultimate load is minimal. These results demonstrate that CFRP reinforcing bars can be used as an alternative to existing steel plate/screw systems. Although CFRP plate connectors show lower ultimate strength, bending stiffness and ductility, the performance of the system can be further improved by using sufficient anchorage systems at the end of CFRP plate within the concrete.

Reinforcement of ancient floors by timber–concrete composite systems with collar connector

Timber–concrete composite (TCC) systems have been successfully used in built heritage. They provide an efficient solution for improving the seismic response of masonry buildings in which timber floors are generally used. TCCs commonly consist of a thin concrete slab connected to the timber beams by connectors. The paper focuses on a steel collar connector, appropriately conceived for surrounding the timber beam, avoiding any drilling into the wood. It is composed of parts bolted at appropriate wings, with the superior one or purposely welded studs working as connectors. A rubber layer interposed between the collar and beam can both reduce damage to the beam surface and ensure the adaptability of the system to irregular surfaces if applied to existing beams. Friction at the wood–(rubber)–steel surface is guaranteed by bolt tightening. This paper describes the experimental and numerical research activity carried out. Monotonic push-out tests were performed on different types of collars, which allowed the evaluation of the system behaviour and failure modes, with the aim of system optimisation. Bending tests on either timber–concrete beams or a full-scale floor equipped with collar connectors were also performed. An application of the TCC system with collar connectors to a historical timber floor is briefly described.

Analytical evaluation to the timber-concrete composite beam connected with notched connections

Timber-concrete composite (TCC) floor systems that combine the material merits of timber and concrete are gaining increasing interest from builders and designers around the world. The connections in the TCC system that marry timber and concrete together are the essential part that dominates the structural efficiency of the composite system. The most commonly used connectors such as steel fasteners are often closely spaced, which can be designed assuming continuous shear force transmission between timber and concrete. The notched connections in TCC systems are often widely and unequally spaced, thus shear forces are only transferred at discrete positions that should not be smeared along the entire beam. To determine the deflection, stress distribution, and relative slip between timber and concrete along the composite beam connected with notches, an analytical method with a simple release-and-restore procedure is proposed in this study. Both the discrete and semi-rigid features of the connectors are considered in the method. The proposed method is validated by comparing its predictions with those from other existing composite beam models and a finite element model through two examples. The discontinuous distribution of internal forces and stresses in the composite beam caused by discrete connections can be well captured by the proposed method. The proposed analytical procedure in this study can be used to facilitate the optimum design of TCC systems with discrete connection systems.

Long-term performance of timber-concrete composite systems with notch-screw connections

This paper presents the experimental results of long-term tests performed on six push-out specimens, one timber-concrete composite (TCC) beam with notch-screw connections, and one timber beam. The interface slip of shear connections was evaluated in a constant temperature and humidity environment, and two loading cases (15% and 30% of the ultimate bearing capacity of push-out specimens) were considered. After 342 days of loading, the long-term slip for the push-out specimens with 0.15 and 0.30 loading levels were 0.221 mm and 0.338 mm, respectively. The beam specimens were tested in an uncontrolled indoor environment. The long-term loads sustained by the beam specimens were approximately 18.8% of the short-term flexural capacity. After more than 400 days of loading, the maximum mid-span deflection of the timber beam and TCC were 4.25 and 4.20 mm, respectively. The timber strain and the interface slips of the TCC specimen showed more obvious environmental sensitivity than the mid-span deflection. Three existing creep models and a modified model were adopted to fit the long-term slip curves of the push-out specimens. The modified model showed the best fitting accuracy with the recorded data, and the most reasonable prediction tendency for the whole service life. The final mid-span deflections of beam specimens were predicted by the modified model for the 50-year service life, and the predicted results for the timber beam and TCC were 12.7 mm and 10.1 mm, respectively. These results are in good agreement with the calculation results according to Eurocode 5 and NDS-2018.

Experimental study on notched connectors for glulam-lightweight concrete composite beams

A new type of structural element, the timber-concrete composite beam, exhibited excellent structural performance. The notched connector is widely used in timber-concrete composite systems as a result of its considerable shear capacity and stiffness. Six groups of push-out tests were performed to investigate the shear performance of the notched connectors for the timber-concrete composite beams, with consideration to the varying concrete types, the shear length of the timber, and whether the notch was reinforced. From the test results, the notched connectors that corresponded to the shear fracture of concrete or timber had a low shear capacity and poor ductility. Notched connectors that simultaneously failed at the concrete slab (via shear force), as well as at the lag screw reinforcement point during bending presented the greatest shear capacity. This was followed by the notched connectors that exhibited diagonal-compression failure at the concrete slab. Screw fasteners in the notch were shown to improve the strength, ductility, and post-peak behavior of the notched connectors. In addition, the concrete type, the shear length of the timber, and whether the notch was reinforced were found to have no major influence on the slip modulus of the notched connectors.

Experimental investigation on innovative connections for timber–concrete composite systems

Abstract A series of innovative connections with the different combinations of steel plates and screws was developed for timber–concrete composite (TCC) system in this paper. Several groups have introduced vulcanized rubber layer to the jointing steel plate, which was used to be glued onto the timber beam surface. Push-out tests were carried out on the proposed connections and three replicates were prepared for each series. The study focused on the load carrying capacity, slip modulus, ductility and the role of some factors of the innovative connections. Moreover, the load-slip behaviour was evaluated based on an existing non-linear model and parametric analysis was also conducted. The research results showed that this connecting system looks suitable for structural application.

Finite Element Modelling of the Connection for Timber-concrete Composite Beams

The present study investigated the structural behaviour of the connection for timber-concrete composite (TCC) beams using numerical analysis. In the proposed TCC system, a concrete slab was connected to timber girders with mechanical shear connectors developed by the authors of this article. The load-slip behaviour of the connections was characterised in the push out test. Non-linear 3D finite element (FE) models of the tested joints were verified against experimental results. The comparison between the experimental and numerical results indicates that the adopted 3D model can adequately capture the response of the TCC joints.

Deconstructable timber-concrete composite beams with panelised slabs: Finite element analysis

This paper deals with the development of efficient and accurate numerical models for the analysis of deconstructable timber-concrete composite (TCC) beams with panelised reinforced concrete (RC) slabs. Three different methods, viz. analytical, 1D frame finite element (FE) and 2D continuum-based FE models, are proposed and validated against experimentally measured data from 4-point bending tests conducted on TCC beams with precast panels. It is shown that the analytical model is the most efficient, whereas the 2D continuum-based model is the most accurate among the three different methods considered. In addition, a parametric study is carried out using 2D FE models to assess various aspects of the TCC system and to evaluate the influence of precast panelised RC slabs on the structural response of TCC beams. Lastly, the challenges of the practical FE modelling of deconstructable TCC beams are briefly discussed and accordingly, some guidance on the FE analysis of TCC beams with panelised RC slabs is provided.

Time-dependent Reliability Analysis of Timber-Concrete Composite Beams

Timber-concrete composite system is increasing the use of timber in construction because some structures could not be built by timber alone, but it becomes possible with this composite system. The deterioration of structures in service is generally uncertain over time, therefore the appropriate approach for the structural analysis is a time-dependent reliability analysis that considers the randomness and uncertainties of deterioration process over a time period. This paper describes two methods for time dependent reliability analysis, random variable deterioration rate model and gamma process model, and compares the deterioration prediction as well as service life estimation of timber-concrete composite beams under normal use based on proposed models.