Behaviour of timber infilled cold-formed steel tubular short columns under monotonic and cyclic compression: An experimental study

Timber-steel composite elements have shown to be effective, compared to traditional timber elements, as they are relatively lighter and equally efficient in resisting structural effects. This paper reports the outcome of an experimental study conducted to evaluate the performance of Timber infilled steel tubular (TIST) columns under axial compression. Two types of TIST column sections (square and circular) were fabricated and tested, along with two different types of steel tubular thicknesses (1.4 mm and 2.4 mm). In total, 40 TIST column specimens were subjected to monotonic and cyclic compression. The experimental findings are reported in terms of failure modes, axial compression resistance and load-deformation characteristics gathered from the tested TIST column specimens. All the tested TIST columns have failed by local axial buckling of steel tubes, followed by crushing or combined crushing and shear failure of timber sections. Further, the load-deformation characteristics observed in monotonic and cyclic loaded TIST columns are different, where slightly less axial load capacities were achieved in cyclic loaded columns, with relatively higher axial deformation characteristics. The cyclic compression capacities of the TIST columns are about 5-15 % lower than the corresponding monotonic capacities. In addition, the shape of the TIST section and slenderness of the steel tubes affect the axial compression behaviour of the columns. The design formulations suggested to determine the axial resistances of concrete infilled steel tubular (CIST) sections were used to examine the axial resistance of TIST columns, where instead of concrete properties, the infilled timber properties have been substituted. Subsequently, the considered formulations have been shown to conservatively predict the axial resistance of the TIST column specimens.