A study on enhanced mechanical properties of wood in the parallel-to-grain direction in timber-filled-steel tubular columns

This study investigates the enhancement of timber’s compressive strength when confined within steel hollow sections, a concept well-established in concrete-filled tubular columns, where confinement significantly improves strength. Despite the growing interest in hybrid steel-timber construction, the confinement effect on timber remains unexplored. Expressions are presented to predict the enhanced compressive performance of timber-filled steel tubular (TFST) columns with circular and square steel sections. Constitutive models of unconfined Radiata pine (Softwood) in compression are developed from physical tests. A series of compressive tests are conducted on timber-filled-steel-tube (TFST) stub columns with different wall-thickness to outside width ( t / b ) ratios in square hollow sections (SHS) or thickness to outside diameter ( t / d ) ratios in circular hollow sections (CHS). Analytical models and finite element analyses (FEA) are validated against test results and are used to develop stress-strain models for the confined timber. A notable increase is observed in the compressive yield capacity of timber confined by thick-walled steel tubes. Based on the experimental observations and numerical models, theoretical constitutive models for the mechanical properties of confined timber in compression parallel to the grain are provided. • Timber-filled-steel-tubular stub columns with SHS and CHS outer steel sections are manufactured and tested in compression. • The effect of confinement of timber in the parallel to the grain direction is investigated using physical tests, analytical models, and numerical simulations. • The results show notable enhancement of yield strength and ductility in confined timber. • The timber inserts significantly delay the local buckling of the outer steel profile.