Researchers have now developed a simple yet effective moment-resistant joint for timber-concrete composite (TCC) frames, marking a significant step forward in improving load transfer and structural integrity in hybrid systems.
Study: Experimental and numerical investigations of a timber-concrete composite frame joint for high-rise buildings. Image Credit: Hanna Taniukevich/Shutterstock.com
The study, published in Engineering Structures, presents a new joint design, developed using suitable materials and a straightforward assembly process. The joint was assessed for its ability to transfer bending moments, as well as normal and shear forces, under both horizontal and vertical loads.
Background
Timber-concrete composite structures are gaining traction in construction due to their environmental benefits and superior performance compared to pure timber. TCC systems offer improved acoustic insulation, fire resistance, and greater load-bearing capacity in bending.
A key factor in the effectiveness of TCC structures lies in the materials used and, critically, the stiffness of the composite connection—largely dictated by the type of shear connector. While beam-to-column connections in TCC systems are commonly bolted, these often fail when subjected to tensile stress perpendicular to the timber grain, particularly in floor systems.
To address this, new shear connectors with optimized stiffness are needed. In response, the study discussed proposes a novel joint design for TCC frames, along with an analytical method to calculate the joint’s rotational stiffness.
Methods
The timber components were made from beech laminated veneer lumber (LVL) using a CNC joinery machine. Steel elements, including embedded parts and plates, were milled and welded in a workshop. Concrete was mixed in-house to maintain consistency across test specimens.
After preparing each component, the timber and steel parts were assembled on horizontal supports, aligned, and fixed in place. Once the frame was erected, the concrete slab formwork was installed, followed by reinforcement placement and concrete pouring. The fully assembled test specimens were then mounted on a test bench.
Testing was force-controlled to account for differences in composite beam stiffness relative to force direction. Loads were applied incrementally until failure, while strains and deformations were tracked using 25 strain gauges, two rosettes, and nine inductive displacement transducers.
Numerical simulations were also conducted using ANSYS Workbench. The models accounted for material non-linearity and were solved using the Newton-Raphson method. A 3D model helped visualize multidimensional stress states and identify complex load transfer and deformation mechanisms.
Results and Discussion
Load-deformation and moment-rotation diagrams were used to assess the experimental specimens. Results showed beam-to-column rotations between 12–32 milliradians, end-beam displacements of 42–69 mm, and relative movements between composite partners ranging from 0.35–1.3 mm. Specimens with transverse tension reinforcement exhibited partially ductile behavior.
Numerical results closely matched the experimental vertical deformations at beam ends, with discrepancies under 10 %. However, the rotational stiffness in simulations was generally lower than that observed experimentally. Notably, there were inconsistencies in measuring local strains and relative displacements between timber and concrete components.
Parameter analysis also highlighted that the concrete’s dilatancy angle significantly affected strain development, while friction played a major role in the deviation of relative displacement. A more detailed model of load transfer points could yield even more accurate results.
Further stress analyses identified deformation zones within the joint and their corresponding stiffness, summarized in a spring model. This was paired with a strut-and-tie model to depict the forces involved. The combination of analytical and experimental findings confirmed the validity of the approach and helped clarify how loads are optimally transferred in the system.
Conclusion and Future Outlook
The study offers a detailed examination of a newly developed moment-resistant TCC frame joint, particularly suited for high-rise buildings. Both experimental and numerical methods highlighted the importance of material choice and simplified assembly.
Key takeaways include insights into failure behavior, initial points of failure, and the joint’s bending and rotational capacity. Tests using beech LVL specimens with varying dimensions and concrete strengths helped explore a wide range of design conditions.
However, further development is needed to refine the joint for real-world use. Future studies should explore how the joint performs under additional loading scenarios, including gravity loads, seismic activity, and wind forces. Understanding how these loads affect initial stiffness—and by extension, hysteresis behavior—will be crucial for advancing the design.
Journal Reference
Höltke, T. & Bleicher, A. (2025). Experimental and numerical investigations of a timber-concrete composite frame joint for high-rise buildings. Engineering Structures, 333, 120034. DOI: 10.1016/j.engstruct.2025.120034, https://www.sciencedirect.com/science/article/pii/S0141029625004250
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