Rational building systems for medium to long-span timber structures

The aim of this research project is to explore the possibility of producing a new type of building system for resource-efficient, medium to long-span timber structures. The idea is based on designing new types of easy-to-assemble wooden connections with high-strength birch plywood replacing conventional steel plate systems. Building systems for adaptive assemblages will be made in a digitized controlled process of standardised parts, where the design itself is optimised to fit 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.

The results showed that birch plywood has excellent mechanical properties, especially in plane with different load angles. The lowest tensile and compressive strength was observed at a 45-degree load angle, but this is compensated by high shear strength. Tests of frame corners on a lab scale with birch plywood showed that the technique can handle complex stress states. The conclusion is that birch plywood has the potential to replace steel plates in wooden structures and that analytical and numerical models can provide satisfactory estimates of the strength and stiffness of the joints. The full-scale tests of frame corners showed that glued joints were 27% stronger and 33% stiffer than screwed joints. Failure in glued joints occurred in the frame leg, while failure in screwed joints occurred in both the frame leg and the frame beam. As a final step in the project, a variant of the developed joint has also been tested in a demonstration building.

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