In timber-concrete composite systems, timber and concrete are inherently brittle materials that behave linearly elastic in both tension and bending. However, the shear connection between the members can exhibit significant ductility. It is therefore possible to develop timber-concrete composite systems with ductile connection that behave in a ductile fashion. This study illustrates the use of an elastic-perfectly plastic analytical approach to this problem. In addition, the study proposes an incremental method for predicting the nonlinear load-deflection response of the composite system. The accuracy of the analytical model is confirmed with a computer model, and numerical solutions of the analytical model are compared to experimental results from the bending tests conducted by previous researchers. Reasonable agreement is found from the comparisons, which validates the capacity of the analytical model in predicting the structural behaviour of the timber-concrete composite systems in both elastic and post-elastic stages.
Over the last two decades many constitutive models with different degrees of accuracy have been developed for analysis of sawn timber and engineered wood products. However, most of the existing models for analysis of timber members are not particularly practical to implement, owing to the large number of material properties (and associated testing) required for calibration of the constitutive law. In order to overcome this limitation, this paper presents details of 1D, 2D and 3D non-linear fi nite element (FE) models that take advantage of a quasi-brittle material model, requiring a minimum number of material properties to capture the load-defl ection response and failure load of timber beams under 4-point bending. In order to validate the model, four tapered timber piles with circular cross-section (two plains and two retrofi tted with steel jacket) were tested and analysed with the proposed 3D FE modelling technique; and a good correlation between experimentally observed and numerically captured ultimate load was observed. Consequently, it was concluded that the developed FE models used in conjunction with the quasi-brittle constitutive law were able to adequately capture the failure load and load-defl ection response of the fl exural timber elements.
Long-span timber floor elements increase the flexibility of a building and exhibit a significant market potential. Timber floor elements are endeavouring to fulfil this potential, but building projects employing long-span timber floors have encountered drawbacks. High costs and vibration performance are challenging, and the timber industry is under substantial pressure to find attractive solutions for building components with otherwise favourable environmental features. Only a few existing studies have investigated serviceability sensitivity in relation to timber floor connections. Interconnections are inexpensive to produce and install and may offer a resource-efficient approach to improving serviceability performance. In the present study, the effect of interconnections is investigated in a full-scale structural test. Floor elements positioned in different configurations have been tested for static and dynamic performance using different types of interconnections. The observed effects of interconnection types vary according to the configuration and direction of mode shapes, and are assessed in terms of shift in frequency, damping and resonant energy. These can all be utilised in combination with observed differences in the deflection parameter. The present work demonstrates that connections between timber elements have significant effects on timber floor serviceability and may offer interesting solutions to improve the vibration performance of long-span timber floors.
This paper reports the results of experimental push-out tests on three different types of timber–concrete composite (TCC) connections, including normal screw, SFS and bird-mouth. The load-slip diagrams obtained from lab tests are employed to calculate the slip modulus of the connections for serviceability, ultimate and near collapse cases based on Eurocode 5 recommendations. Additionally, four full-scale TCC beams with normal screw, SFS and bird-mouth are constructed and tested under four-point bending within the serviceability load range to verify the slip modulus of connections which derived from the push-out tests. Further, based on the experimental results and using nonlinear regression, an analytical model each one of the connections is derived which can be easily incorporated into nonlinear FE analyses of TCC beams.
Timber beams can effectively be reinforced using externally bonded fibre reinforced polymer (FRP) composites. This paper describes a nonlinear 3-dimensional finite element model which was developed in order to accurately simulate the bending behaviour of unreinforced and carbon FRP plate reinforced glulam beams. The model incorporates suitable constitutive relationship for each material and utilises anisotropic plasticity theory for timber in compression. Failure of beams was modelled based on the maximum stress criterion. The results of the finite element analysis showed a good agreement with experimental findings for load-deflection behaviour, stiffness, ultimate load carrying capacity and strain profile distribution of unreinforced and reinforced beams. The proposed model can be used to examine the effect of different geometries or materials on the mechanical performance of reinforced system.
Mass Timber Panels (MTP) are a new generation of engineered wood panels that are available in large plane dimensions to facilitate fast floor construction with the obvious environmental benefit of being from a renewable material. In floor construction, concrete slab or topping is often applied over the MTP panels to improve various performance attributes, including structural, acoustic and vibration serviceability. Mass Timber Panel-Concrete (MTPC) composite floor system often consists of a Mass Timber Panel (MTP) connected to the concrete layer with mechanical connectors such as Self-Tapping Screw (STS) and a sound insulation layer in between the MTP and concrete. Lack of design standards and guidelines are the most important barrier limiting wide spread use of this MTPC composite floor system.
The capacity of this type of composite system mostly depends on the strength of the interlayer connection. Also, the allowable floor span is often governed by serviceability performance requirements, such as deflection and vibration, which are directly dependent on the stiffness of the interlayer connection. Usually, connection tests are performed to characterize connection strength and stiffness required for structural design. In this research, three types of MTPs with normal weight concrete, three insulation thicknesses, two screw embedment lengths and two screw angles were tested to characterize connection strength and stiffness. Test results showed that connections with screws at an insertion angle of 30-degree had a larger strength and stiffness than connections with screws inserted at a 45-degree angle. Stiffness appears to be more sensitive to the presence of an insulation layer compared to strength. Overall, 5-15% and 22-34% reduction of strength and 35-50% and 55-65% reduction of serviceability stiffness were noticed for an insulation thickness of 5 mm and 15 mm, respectively. In lieu of testing, analytical models can be developed to directly calculate connection strength and stiffness based on component properties. To that end, two analytical models each were developed for solid and layered timber, for directly predicting the stiffness and strength of a connection with inclined screws and an insulation layer. Usually, connection properties of laterally loaded connection is controlled by the dowel bearing effect of the fastener in timber, but inclined screw connection has a more complex behaviour due to the combined bearing and withdrawal action of the screw. Therefore, in the developed models, both the bearing and withdrawal actions of the screw are considered. The connection stiffness and strength model were validated with the connection tests with a wide range of parameters. It was found that the strength models are capable of predicting the mode of failure of a connection and the load-carrying capacity within 10% of the experimental value, while, the stiffness models are capable of predicting the stiffness of connection to within 18% of the experimental value.
The commonly used Gamma method to design a timber-concrete composite floor has limitations and cannot predict the load-carrying capacity, bending stiffness and failure modes of the composite floor system when there are widely spaced discrete connectors. Therefore, an analytical model has been developed considering the interlayer connector behaviour under the elastic-plastic range along with an acoustic layer between timber and concrete, to predict the capacity, bending stiffness, failure modes and the load-deflection response of MTPC composite floor system. One-way acting composite floor panels were also tested under four-point bending with different configurations to investigate the influence of different parameters and to validate the developed system prediction model. It was found that the model is capable of predicting the capacity of the MTPC composite system within the range of -6% to +26%, bending stiffness within the range of -15% to +10% of the bending test values and the associated failure mode. The Gamma method cannot predict the system capacity, and it tended to over-estimate the bending stiffness on average by 43% and was found not appropriate for MTPC composite system with discrete shear connectors and MTP. This developed connection and system models for MTPC composite floors will facilitate the use of such a system in mass timber construction.
This article presents the concept of the stub girder flooring system adapted to timber structures. The floor system consists of LVL beams covered by CLT floor panel separated by a series of short shear connection called stubs. The paper focusses on the analytical development to predict the optimized flooring system dimensions for future experimental tests. The proposed model contains structural parameters such as the main girder and secondary Gerber beam, the stubs and the CLT panel with various materials. This initial investigation into this concept suggests that the flooring system can be a possible alternative for mid to long span frames.