American Society of Civil Engineers


Fire Design of Timber-Concrete Composite Slabs with Screwed Connections


by Andrea Frangi, Ph.D., (corresponding author), (Senior Scientist, ETH Zurich, Institute of Structural Engineering, Wolfang-Pauli Strasse 15, 8093 Zurich, Switzerland E-mail: frangi@ibk.baug.ethz.ch), Markus Knobloch, Ph.D., (Senior Scientist, ETH Zurich, Institute of Structural Engineering, Wolfang-Pauli Strasse 15, 8093 Zurich, Switzerland. E-mail: knobloch@ibk.baug.ethz.ch), and Mario Fontana, Ph.D., (Professor, ETH Zurich, Institute of Structural Engineering, Wolfang-Pauli Strasse 15, 8093 Zurich, Switzerland. E-mail: fontana@ibk.baug.ethz.ch)

Journal of Structural Engineering, Vol. 136, No. 2, February 2010, pp. 219-228, (doi:  http://dx.doi.org/10.1061/(ASCE)ST.1943-541X.0000101)

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Document type: Journal Paper
Section Heading: Special Design Issues
Abstract: The structural behavior of timber-concrete composite slabs is mainly governed by the shear connection between timber and concrete. When a timber-concrete composite structure is exposed to fire, it is of particular importance to know the changes in stiffness and strength that the shear connection is subjected to. For the calculation of the fire resistance of timber-concrete composite slabs a simplified design method was developed on the basis of the calculation model for mechanically jointed beams with flexible elastic connection given in EN 1995-1-1 and the reduced cross section method given in EN 1995-1-2. The effects of temperature on the mechanical properties of timber, concrete, and connection are taken into account by modification factors kmod,fi. For the strength and stiffness properties of the screwed connections simplified formulae for the calculation of the modification factors kmod,fi were developed, based on the results of an extensive experimental study on the fire behavior of the screwed connections. The modification factors kmod,fi were expressed as a function of the side cover of the connections. In this way the temperature in the timber member does not need to be determined, making the calculation of the strength and stiffness properties of the screwed connection in fire much easier for the designer. The paper first describes and discusses the behavior and modeling of the screwed connection in fire, and then the simplified design method developed for the calculation of the fire resistance of timber-concrete composite slabs with screwed connections is presented. Finally, the result of the calculation method is compared to the result of a full-scale fire test.


ASCE Subject Headings:
Wood
Concrete
Slabs
Connections
Fires
Tests
Composite structures

Author Keywords:
Timber
Composite slab
Shear connection
Fire
Charring model
Charring rate
Fire tests
ISO-fire exposure
Design model