By Nidhi DhullReviewed by Susha Cheriyedath, M.Sc.Aug 6 2024A recent article published in Case Studies in Construction Materials proposed novel adhesive-free edge connections for cross-laminated timber (CLT) panels. The flexural performance of CLTs with these connections was examined under four-point bending tests through numerical modeling and verified experimentally.
Verification model (numerical model No. 1): (a) discretization of FE model and (b) assembled FE model. Image Credit: https://www.sciencedirect.com/science/article/pii/S2214509524001268
Background
Timber has become a popular building material due to its superior environmental performance than concrete and steel. CLT is preferred over traditional materials based on energy, convenience, and environmental prospects. Moreover, CLT exhibits good mechanical and thermal performance in structural applications.
However, the performance of timber structures relies on robust connections to address their inherent limitations. Various types of connections are employed to enhance the structural performance of CLT, with steel and adhesive connections being the most common due to their high stiffness, lightweight nature, ease of construction, and durability.
Despite their advantages, steel connections are susceptible to corrosion over time, and adhesives can emit harmful compounds, such as formaldehyde, during use. Furthermore, manufacturing and installing steel connections require more material and energy compared to timber connections, while adhesives are costly and have significant global warming potential.
To address these issues, this study proposes the use of adhesive-free edge connections for CLT panels. This approach aims to improve the sustainability, extensibility, environmental impact, and transportation convenience of timber structures.
Numerical Methods
CLT panels with custom-designed joints were numerically simulated to assess their flexural performance. These simulations were conducted using the finite element (FE) software ABAQUS. Given that timber is an orthotropic material with varying properties in different directions, the VUSDFLD subroutine was utilized to define multiple orthotropic materials within the same simulation.
The numerical model was validated through three experimental tests. The first and second validation models were compared against a four-point bending test of glued-laminated timber (GLT) beams with compressed wood (CW) connectors. The third validation model was compared with a four-point bending test of an adhesive-free CLT panel.
Following validation, the model was used to develop and analyze four new adhesive-free edge connections for CLT panels: the Belt (B) edge connection, T-shape edge connection, Grove-and-Tongue (GT) edge connection, and G edge connection.
Each connection was subjected to four-point bending tests and 41 parametric investigations, considering factors such as connector geometry, dimensions, and material types. The performance of these edge connections in CLT panels was evaluated in terms of ultimate loads, strains, displacements, moment capacities, failure modes, and effective stiffness. Additionally, the study examined factors influencing the load-bearing capacity of the edge connections.
Results and Discussion
The CW connectors explored in this study offer promising alternatives to steel and synthetic adhesives in CLT-based construction. The performance of these connectors varied across different designs during the parametric analysis.
For the B edge connection, the dovetail connector's load-bearing capacity increased by up to 29 % with greater longitudinal length. Expanding the distance between two connectors improved the capacity by 5 %, and increasing the distance between the connector hole and the CLT panel’s mid-span axis boosted it by 9.5 %.
The T-shape edge connection demonstrated substantial improvements with specific modifications: reducing the web surface angle increased capacity by 38 %, minimizing the lateral distance between connectors raised it by 23 %, and increasing the width and thickness of the connector’s flange resulted in an impressive 222 % increase. Notably, the T-shape connection with a narrow-angle web surface showed superior performance under compressive loads compared to tensile loads.
For the GT edge connection, using CW as the second lamella layer increased load-bearing capacity by 65 %, while reducing the rib angle at the groove-tongue connection surface improved it by 47 %.
The G edge connection's load-bearing capacity increased by 6 % with a shorter external connector length, and using either a dowel (10 % increase) or a rectangular-shaped connector (66% increase) further enhanced performance. Importantly, failures were observed in the connectors rather than the CLT panels, underscoring the critical importance of connector strength.
Conclusion and Future Prospects
Overall, the researchers successfully developed novel adhesive-free timber edge connections for wooden floor systems, enhancing the expandability and energy performance of CLT panels and promoting sustainability in construction. The study highlighted the effectiveness of simulation techniques in assessing both the mechanical performance of existing structures and the potential of new designs.
The various geometries and dimensions of timber connections examined in this research provide valuable insights for designing adhesive-free edge connections for CLT panels, which are frequently used as floor elements. The validated numerical models and parametric analysis offer a solid foundation for simulating connected mass timber panels using FEM.
Looking ahead, the researchers aim to further explore the development of additional adhesive-free timber edge connections through numerical methods. Future investigations will focus on testing different connection sizes across various dimensions and types of CLT constructions, as well as analyzing the shear strength of the connectors.
References and Further Reading
Ren, H., Bahrami, A., Cehlin, M., & Wallhagen, M. (2024). Proposing New Adhesive-Free Timber Edge Connections for Cross-Laminated Timber Panels: A Step Toward Sustainable Construction. Case Studies in Construction Materials, e02975. DOI: 10.1016/j.cscm.2024.e02975, https://www.sciencedirect.com/science/article/pii/S2214509524001268
Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.