Orthogonal distribution and dynamic amplification characteristics of partially prefabricated timber-concrete composites

Abstract

Timber-concrete composites (TCCs) are structurally efficient, low carbon floor systems that can be prefabricated to accelerate in-situ construction. The timber-concrete connectors and their immediately surrounding volumes of concrete together perform important orthogonal structural functions. Longitudinally, they enable slab - joist composite action, thereby improving vertical distribution of bending stresses within each TCC T-section. Transversely, they enable continuity of the slab across the joists, thereby influencing transverse distribution of moments in the TCC. This paper reports field tests to characterise such orthogonal action. Human static and dynamic loads were applied, within the timber-framed Kantor Centre of Excellence building in London, to the newly constructed TCC floor comprising precast concrete planks fastened via partially prefabricated connections to multiple beech LVL joists. Strains recorded from multiple levels on the joists indicate TCC neutral axis heights consistent with almost full composite action, implying excellent vertical distribution capability. Back-calculations from these strains show significant transverse distribution of midspan moments, with 64% and 14% of the loaded T-section's moment developing at one and two T-sections away respectively. The test results further reveal dynamic amplification factors up to 2.38 on peak moments. Moreover, the test results linked to grillage analyses suggest that transverse distribution of midspan moments may be influenced by partial restraint at the supports. It is concluded that the partially prefabricated connections possess excellent orthogonal distribution characteristics.