Radiata Pine and Douglas Fir Timber Steel Encased Columns Subjected to Concentric and Eccentric Loading
L. Kia, Hamid Valipour
Abstract
Composite timber steel encased columns comprising low-grade coniferous softwood radiata pine (Pinus radiata) (MGP10 grade) and Douglas fir (Pseudotsuga menziesii) (F7 grade) with encased steel bars (yield strength of 300–660 MPa) were fabricated and tested under concentric and eccentric loads. The timber lamellae and encased steel bars were bonded together with a two-component epoxy adhesive and mechanical fasteners to achieve a composite member that combines the lightweight and ductile behavior of timber in compression with the high strength of steel bars. The structural performance of the columns was evaluated with respect to control bare timber samples. The test results revealed that stiffness and load-carrying capacity of the stocky composite columns (slenderness ratio ρcS<10, per AS1720.1) were significantly increased (over 100% in some cases) by the encased steel bars. The hybridization of timber columns with steel bars was also effective in reducing the variance in the load-carrying capacity. An analytical model based on a simplified bilinear elastoplastic relationship and principles of structural mechanics was proposed to estimate the stiffness and load-carrying capacity of the composite columns under axial compression and bending moment.