Mass timber buildings are rapidly becoming popular around the world, due to recent changes in the standards, development of engineered wood products, fire compliancy, low carbon emissions, advancements in design for manufacturing technologies, prefabrication and ease of installation. However, timber can be combined with existing construction materials such as concrete and steel to develop smart systems that are robust and cost-efficient. Some recent iconic examples are: (i) Mjøstårnet building in Norway, (ii) NADAAA's new residence hall in New England, (iii) RISD Quad Residence Hall in the US and (iv) Arbo building in Switzerland.

In this project by mimicking the concrete-filled steel (CFST) tubular column concept, timber-filled steel tubular (TFST) structural elements (columns and beams) are developed. The manufacturing process includes inserting solid timber into steel tubes without using adhesive. The timber expands as the moisture content (MC) increases causing a tight fit. This will produce a hybrid steel-timber structural element that has the benefits of a composite material.

This study explores the synergy of these materials in creating lighter, taller, and more sustainable structures through the development of small-scale hybrid steel-timber modules, such as fibre-filled steel tubular (FFST) beams, columns, and frames, fabricated without adhesives by embedding dried wood fibres into cold-formed steel hollow sections. The resultant FFST elements demonstrated a notable enhancement in axial and flexural stiffness and strength - up to 55% greater than steel-only counterparts, along with improved weight-to-performance ratios. Alongside, the research extends to evaluating the compressive behaviour of timber confined by steel tubes. Through a combination of material testings, analytical modelling, and finite element analysis (FEA), this research establishes theoretical and constitutive models for the mechanical properties of confined timber, revealing significant increases in compressive yield capacities, particularly in timber confined by thick-walled steel tubes. This comprehensive analysis concludes in the derivation of design rules from regression analyses, effectively predicting the capacities of TFST columns, which demonstrate enhanced efficiency in a six-story office building case study, suggesting broader applicability in mid-to-high-rise construction. This integrative approach not only supports the trend towards circular economies by allowing for the rework and recycling of wood products but also facilitates the upscale potential of FFST frames in residential and low-rise commercial buildings.