Potential of continuous nail-laminated timber concrete composite slabs to cover large spans with timber
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Date
2024
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Abstract
This study examines the flexural performance of six 9-m full-scale Nail-Laminated Timber Concrete (NLTC) composite slabs with continuous Boundary Conditions (BC)s. The slabs were made with lumber beams edge-joined with double nailing, end-joined with butt joints, and the reinforced concrete topping connected with a set of notches, inclined screws, or a combination of both. This slab configuration provides large-span continuous BCs, reducing their deflections in a simple and effective way. Five-point monotonic bending tests were considered for all slabs. Before full-scale slabs, compressive and tensile pull-out tests of Timber-Concrete Composite (TCC) shear connections were performed, including notches and inclined screws. Tensile pull-out tests were added to assess whether the shear connectors had dissimilar behavior under the negative bending moments expected in these unconventional BCs. Failure modes, load–mid-span deflection relation, bending stiffness, and timber-concrete slip were evaluated for all slabs. A detailed 3D micro-Finite Element (FE) model of the shear connections was built in ANSYS software, whereas a macro-FE model of NLTC slabs was made in SAP2000, demonstrating a good fit for the timber-concrete interaction and the load-carrying capacity of the composite slab under these unconventional BCs at the serviceability range, respectively. Moreover, an analytical elastic beam with the Girhammar method for continuous TCC slabs was assessed and demonstrated as more precise than the traditional -method. Predictions of the numerical and analytical (Girhammar) models for the bending stiffness at service loads up to 30% of capacity showed errors up to 10% and 57%, respectively. This study demonstrates that achieving continuous boundary conditions may be an effective way for applying timber in modern large span applications.
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Keywords
Timber-concrete composite, Bail-laminated timber, Flexural performance, Hybrid timber-concrete building, Propped cantilevered slab, Notched and screwed connections, Pull-out test