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Experimental behaviour of a full-scale timber-concrete composite floor with mechanical connectors

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Abstract

The timber-concrete composite (TCC) beam is a construction technique that can be used for upgrading of existing timber floors without the need of demolition. This possibility has been investigated through full-scale tests on a 6-storey experimental building with light-frame timber walls and platform construction, where the existing timber floor for domestic use was upgraded for reuse as an office building. The acoustic flooring was replaced with a 60 mm lightweight concrete slab, connected to the existing joists with inclined shear connectors (SFS screws) to form the TCC floor. The floor and environmental conditions were monitored during the concrete pouring and hardening, and during the application of the live load. Two different types of construction, propped and unpropped, were compared, and an extensive experimental investigation was performed on material components (lightweight concrete, timber, and connection system) with the aim to fully characterise the behaviour under short- and long-term loading. The unpropped floor was then tested to failure under monotonic loading, and two different boundary conditions, namely the actual joist-to-wall joint and a perfectly pinned support, were investigated. An advanced FE model was validated on the test results and used to predict the deflection in the long-term. The composite floor achieved the target stiffness and the design load for satisfying ultimate and serviceability limit states for office loading in the UK. The actual joist-to-wall restraint was characterized by a low degree of fixity, however it produced early longitudinal crack formation in the proximity of the support. The final collapse of the floor as a whole occurred progressively under increasing load after failure for fracture in tension of an individual joist. The higher drying shrinkage of lightweight concrete raised the deflection during concrete curing and hardening.

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Acknowledgments

Many thanks are due to the technical support and great expertise provided by Mr. Rob Grantham, formerly Senior Consultant at BRE, UK. The contributions of Francesca Rorato, Ivan Zidarič, and Claudio Nogarol, formerly undergraduate students at the University of Trieste, Italy who were involved in the construction and testing of the composite floors and materials are also gratefully acknowledged. The author also wishes to extend his gratitude to Dr. Vahik Enjily, formerly Head of the Timber Division at BRE, UK who encouraged the writer to apply for funding for this research within the EC TMR Large Scale Facilities Programme.

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  1. Department of Architecture, Design and Urban Planning, University of Sassari, Palazzo del Pou Salit, Piazza Duomo 6, 07041, Alghero, Italy

    Massimo Fragiacomo

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Fragiacomo, M. Experimental behaviour of a full-scale timber-concrete composite floor with mechanical connectors. Mater Struct 45, 1717–1735 (2012). https://doi.org/10.1617/s11527-012-9869-3

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