Steel-Timber Composite Beams as an Alternative to Conventional Steel and Glulam - A Structural and Sustainability Assessment

Abstract

Steel and timber can be combined into hybrid structural elements known as steel timber composite (STC) beams, offering improved structural performance while reducing embodied carbon and cost compared to conventional alternatives. Despite their potential, no dedicated Eurocode provisions currently exist for STC beam de sign, limiting their adoption in practice and motivating the need for further research. This study investigates two STC configurations: STC-1, consisting of a steel HEA section with a glulam element positioned above the top flange, and STC-2, a glu lam beam reinforced with a steel plate on its bottom surface. Both configurations are designed using Newmark’s partial-interaction theory and optimized through a parameter sweep in MATLAB, in which Life Cycle Assessment(LCA) and Life Cy cle Cost (LCC) analyses are performed on the candidate configurations to obtain their CO2 emission and cost performance, with a Marginal Abatement Cost (MAC) framework subsequently applied as the selection criterion. The optimized STC con figurations are then compared against pure steel and pure glulam reference beams. LCA and LCC analyses are conducted across span lengths ranging from 3 m to 12 m, with nonlinear finite element simulations in Abaqus being performed for two representative spans of 7 m and 12 m under office and shopping mall load cases. Results show that STC beams can offer environmental and economic advantages beyond a threshold span length, with STC-1 achieving CO2 reductions of up to 20% relative to the steel reference beyond approximately 5 m, while STC-2 reduces cost up to 30% compared to the glulam reference beyond approximately 9 m. Finite el ement analysis confirms that both configurations exhibit ductile behavior governed by steel yielding, with failure modes and load-displacement responses varying be tween configurations and span lengths. These findings demonstrate that Newmark’s partial-interaction theory provides a viable design basis for STC beams in the ab sence of dedicated Eurocodes.