Rational building systems for medium to long-span timber structures

The aim of this was to explore the potential of developing a new type of building system for resource-efficient timber structures with medium to long spans. The concept focused on designing easy-to-assemble wooden connections using high-strength birch plywood as a replacement for conventional steel plate systems. The building system was developed for adaptive assemblages, produced through a digitized, controlled process using standardized parts, with the design optimized to suit the system.

The purpose of this project was to explore the potential and possibility of producing a new type of building system for resource-efficient, timber structures with medium to long spans. The specific goal was to develop a system for the manufacture of wood-based elements with an increased proportion of bio-based products in structures, connections, and fittings adapted for rational assembly and disassembly of large timber structures. The project also studied and developed production methods that use wood in a more resource-efficient way, which includes simple factory manufacturing and quick, precise assembly on construction sites.Generally, the project has been carried out in four scales:

1. Material properties and details in new connections
2. Testing of new materials and connection details in pilot scale in the lab
3. Full-scale tests to investigate assembly feasibility, stiffness, and strength
4. Testing of a partially modified solution in a full-scale demonstrator.

Results and Conclusions:

• Birch plywood demonstrated excellent mechanical properties, particularly in-plane under varying load angles. Although the lowest tensile and compressive strength occurred at a 45-degree load angle, this was offset by high shear strength.
• Lab-scale tests of frame corners using birch plywood showed the material could handle complex stress states effectively.
• Full-scale tests revealed that glued joints were 27% stronger and 33% stiffer than screwed joints. Failures in glued joints occurred in the frame leg, while failures in screwed joints affected both the frame leg and beam.
• Analytical and numerical models provided reliable estimates of joint strength and stiffness.
• A variant of the developed joint was successfully tested in a demonstration building, confirming the feasibility of the system in real-world applications.

The results indicate that birch plywood has strong potential to replace steel plates in timber structures, contributing to more sustainable and efficient construction practices.

Publications in peer reviewed journals

T Wang, Y Wang, M Debertolis, R Crocetti, M Wålinder, L Blomqvist (2024) Spreading angle analysis on the tensile capacities of birch plywood plates in adhesively bonded timber connections, Engineering structures 315, 118428

Y Wang, T Wang, M Debertolis, R Crocetti, M Wålinder, L Blomqvist (2024) Glulam frame corner joints built of birch plywood and mechanical fasteners: An experimental, analytical, and numerical study. Engineering structures 310, 118112

Y Wang, T Wang, M Debertolis, R Crocetti, M Wålinder (2024) Design of birch plywood as gusset plates in timber-timber uniaxial tension connections: Influence of fastener pattern, face grain orientation, and discussions based on the Whitmore effective width theory. Journal of Building Engineering 86, 108796

T Wang, Y Wang, M Debertolis, R Crocetti, M Wålinder, L Blomqvist (2024) Bonding strength between spruce glulam and birch plywood at different load-to-plywood face grain angles. European Journal of Wood and Wood Products, 1-13

Y Wang, T Wang, R Crocetti, M Wålinder (2024) Effect of moisture on the edgewise flexural properties of acetylated and unmodified birch plywood: a comparison of strength, stiffness and brittleness properties. European Journal of Wood and Wood Products 82 (2), 341-355

T Wang, Y Wang, J Ringaby, R Crocetti, M Wålinder, L Blomqvist (2024) Glulam beams adhesively bonded by birch plywood plates in moment-resisting beam-to-beam connections. Engineering structures 302, 117471

Y Wang, T Wang, M Debertolis, R Crocetti, M Wålinder, L Blomqvist (2024) Quantifying the load spread angle in plywood gusset plates with mechanical fasteners: experiments, analytical analysis, and validations (Journal Pre-proof)

Y Wang, T Wang, J Ringaby, R Crocetti, M Debertolis, M Wålinder (2023) Testing and analysis of screw-connected moment joints consisting of glued-laminated timbers and birch plywood plates. Engineering Structures 290, 116356

Y Wang, T Wang, R Crocetti, M Schweigler, M Wålinder (2023) Embedment behavior of dowel-type fasteners in birch plywood: Influence of load-to-face grain angle, test set-up, fastener diameter, and acetylation. Construction and Building Materials 384, 131440T 

Wang, Y Wang, R Crocetti, M Wålinder, R Bredesen, L Blomqvist (2023) Adhesively bonded joints between spruce glulam and birch plywood for structural applications: experimental studies by using different adhesives and pressing methods. Wood Material Science & Engineering 18 (3), 1141-1150

Conference proceedings

T Wang, Y Wang, R Crocetti, M Wålinder, P Persson, P Hedlund (2023) Glulam Frames Adhesively Bonded by Means of Birch Plywood Plates: Preliminary Investigations. World Conference on Timber Engineering Oslo 2023, 1453-1461

Popular press

Wang, T., Wang, Y., Debertolis, M., Wålinder, M., Blomqvist, L., Crocetti, R. (2024). Ramhörnförband av björk-plywood för träkonstruktioner. Bygg & teknik 4/24.

Wang, Y., Wang, T., Debertolis, M., Wålinder, M., Blomqvist, L., Crocetti, R. (2023). Innovativa förband med björkplywood. Bygg & teknik 4/23.

PhD theses

T. Wang, "In-plane mechanical properties of birch plywood and its performance in adhesively bonded connections," Doktorsavhandling Stockholm: KTH Royal Institute of Technology, TRITA-ABE-DLT, 244, 2024. 

Y. Wang, "Mechanical connections using birch plywood as gusset plates in timber structures," Doktorsavhandling Stockholm, Sweden 2024: KTH Royal Institute of Technology, TRITA-ABE-DLT, 2410, 2024.

Master theses

Mattia Debertolis, Agnė Laurinavičiūtė (2022) Load-bearing wood connections using birch plywood – An experimental study of birch plywood gusset plates behaviour with mechanical connections, Examensarbete Stockholm: KTH Royal Institute of Technology

Jonatan Ringaby (2022) Moment-resisting connections for glulam using birch plywood: An experimental study on both mechanical and adhesive connections, Examensarbete Stockholm: KTH Royal Institute of Technology

Patrik Hedlund, Pontus Persson (2021) Complex Stress States In Structural Birch Plywood – An experimental study on the behaviour of birch plywood in structural applications, Examensarbete Stockholm: KTH Royal Institute of Technology