Development of Expressive Timber-Steel Hybrid Exoskeletal Systems for Tall Timber Structures

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Copyright: Kia, Layla
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Abstract
Timber construction is rapidly evolving towards high-rise and high-tech. The demand for mid- to high-rise buildings using engineered timber can be attributed to its high structural efficiency and mitigation of carbon dioxide emissions. However, due to the relatively low mass density and stiffness characteristics of timber, lateral load resistance is often the governing criteria for design. Restrictive design regulations, limited education and lack of innovation has seen the development of multi-storey timber structures mimic that of traditional steel and concrete buildings. This has led to the full potentials of timber as a construction material, and timber structures as an architectural form, not to be realised. In this research, an efficient structural system consisting of a timber-steel hybrid exoskeleton is proposed and tested. Specifically, composite timber-steel encased columns and steel-timber buckling restrained braces (STBRB). Experimental testing of composite timber-steel encased columns subjected to concentric and eccentric loading indicates significant stiffness and load carrying enhancement (over 100% in some cases) compared to bare timber columns with intermediate to stocky slenderness. Analytical models based on the principles of structural mechanics and simplified bilinear elastoplastic relationship accurately predicted the load carrying capacity and offers a simple method of analysis which can be used in practice. Detailed nonlinear 3D finite element (FE) simulations of the columns are developed and verified against the experimental results using ABAQUS software. Based on the experimental, analytical, and numerical results, the behaviour of composite timber-steel encased columns is found to be significantly influenced by the ratio of steel strength to timber strength (Asfsy/Atfcm) as well as knots/imperfections, particularly in low-grade wood. Cyclic tests representative of seismic actions on steel-timber buckling restrained braces (STBRB) have demonstrated stable hysteretic energy dissipation and a cumulative inelastic ductility capacity (CID) beyond the requirements prescribed in AISC 341. STBRBs with steel collars placed at the critical ends of the casings demonstrated the highest ductility and energy dissipation. The results from the study showcased the proposed system as a feasible and sustainable alternative to conventional concrete/steel BRBs.
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Publication Year
2022
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Thesis
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PhD Doctorate
UNSW Faculty