Proposal to Account for Concrete Shrinkage and Environmental Strains in Design of Timber-Concrete Composite Beams
Publication: Journal of Structural Engineering
Volume 139, Issue 1
Abstract
Timber-concrete composite beams are statically indeterminate structures where a concrete topping is connected via shear connectors to a timber beam. Because effects such as drying shrinkage of concrete, variations of timber moisture content, and environmental temperature cannot freely occur, self-equilibrated stresses (eigenstresses) and additional deflection are induced in the composite beam and may reduce the structural safety at ultimate and serviceability limit states, respectively. The paper presents a simplified design approach suitable for implementation in codes of practice to account for these effects, which are all transformed into uniformly distributed loads to be combined with gravity load. The moisture content variations to consider in design are tabled based on climatic region, size of the timber section, type of exposure, and protective coating. These variations may become significant particularly for the deflection of composite beams with narrow timber sections exposed to outdoor sheltered conditions. Environmental variations and drying shrinkage of concrete are quite influential on the design, particularly when this is governed by deflection control at a serviceability limit state. Composite beams with solid timber slabs and stiff connection, and composite beams with narrow timber section exposed to outdoor conditions were found to be particularly sensitive to these environmental effects.
Get full access to this article
View all available purchase options and get full access to this article.
References
Ceccotti, A., Fragiacomo, M., and Giordano, S. (2007). “Long-term and collapse tests on a timber-concrete composite beam with glued-in connection.” Mater. Struct., 40(1), 15–25.
European Committee for Standardization (CEN). (2004). “Design of timber structures—Part 1-1: General rules and rules for buildings.” Eurocode 5, Brussels, Belgium.
Fragiacomo, M. (2006). “Long-term behavior of timber-concrete composite beams. II: Numerical analysis and simplified evaluation.” J. Struct. Eng., 132(1), 23–33.
Fragiacomo, M., and Ceccotti, A. (2006a). “Long-term behavior of timber-concrete composite beams. I: Finite element modeling and validation.” J. Struct. Eng., 132(1), 13–22.
Fragiacomo, M., and Ceccotti, A. (2006b). “Simplified approach for the long-term behaviour of timber-concrete composite beams according to the Eurocode 5 provisions.” Proc., Meeting 39 of the Working Commission W18-Timber Structures, R. Goerlacher, ed., Karlsruhe Univ. of Technology, Karlsruhe, Germany.
Fragiacomo, M., Fortino, S., Tononi, D., Usardi, I., and Toratti, T. (2011). “Moisture-induced stresses perpendicular to grain in timber sections exposed to European climates.” Eng. Struct., 33(11), 3071–3078.
Fragiacomo, M., Gutkowski, R. M., Balogh, J., and Fast, R. S. (2007). “Long-term behavior of wood-concrete composite floor/deck systems with shear key connection detail.” J. Struct. Eng., 133(9), 1307–1315.
Fragiacomo, M., and Schänzlin, J. (2010). “The effect of moisture and temperature variations on timber-concrete composite beams.” Proc., 11th World Conf. on Timber Engineering, A. Ceccotti and J.-W. van de Kuilen, eds. Riva del Garda, Italy.
Limträhandbook. (2001). Nordic design manual for glulam, Svenskt Limträ AB, Stockholm, Sweden (in Swedish).
Lukaszewska, E., Johnsson, H., and Fragiacomo, M. (2008). “Performance of connections for prefabricated timber-concrete composite floors.” Mater. Struct., 41(9), 1533–1550.
Schänzlin, J. (2003). “About the time dependent behavior of composite of board stacks and concrete.” Ph.D. thesis, Univ. of Stuttgart, Stuttgart, Germany (in German).
Schänzlin, J., and Fragiacomo, M. (2007). “Extension of EC5 Annex B formulas for the design of timber-concrete composite structures.” Proc., Meeting 40 of the Working Commission W18-Timber Structures, R. Goerlacher, ed., Karlsruhe Univ. of Technology, Karlsruhe, Germany.
Information & Authors
Information
Published In
Copyright
© 2013 American Society of Civil Engineers.
History
Received: Sep 23, 2011
Accepted: Mar 2, 2012
Published online: Mar 6, 2012
Published in print: Jan 1, 2013
Authors
Metrics & Citations
Metrics
Citations
Download citation
If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download.