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The results presented in this paper were developed under the research project Definition of a protocol for the refurbishment of timber floors by connecting with a concrete topping, carried out with the financial support of the Spanish Government within the R&D-2004 National Research Program (reference number BIA2004-07317).

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Timber composite beams with a discrete connection system

Publicat a:Proceedings Of The Institution Of Civil Engineers-Structures And Buildings. 166 (2): 57-72 - 2013-01-01 166(2), DOI: 10.1680/stbu.11.00007

Autors: Fernandez-Cabo, Jose L.; Diez-Barra, Rafael; Fernandez-Lavandera, Jorge; Avila-Jalvo, Jose M.;

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This work centres on a method for the analysis of timber composite beams; the method considers slip in the connection system, based on assembling a flexibility matrix for the whole structure. The lower component of such beams is typically made of timber or glue-laminated timber, while the upper portion is usually either concrete or a timber board, such as laminated veneer lumber or cross-laminated timber. The method is based on a previously proposed solution, but this paper extends the method to the case of a gap between two components with an arbitrary location at the first connector, which notably broadens its practical application. The addition of the gap makes it possible to model a cracked zone in the concrete topping, as well as the case in which forming produces the gap. The arbitrary location of the first connector may, for example, be related to the case of refurbishment. The consideration of induced stresses due to changes in temperature and moisture content is also described, while the concept of equivalent eccentricity is generalised. This method has important advantages in connection with the current European standard EN 1995-1-1: 2004 (EC5), as it is able to deal with any type of load, variable section, discrete and non-regular connection systems, a gap between the two components, and variations in temperature and moisture content. Although it could be applied to any structural system, it is especially suited to the case of simply supported and continuous beams. A simple finite-element method is also proposed in order to compare the results. For the case with smeared connections, the results were compared with an existing exact differential equation; in both cases good agreement was achieved. Examples of working are also given, showing that the connection arrangement notably modifies the shear force distribution. A first interpretation of the results is made on the basis of strut and tie theory. The examples prove that the use of EC5 is unsafe when, as a rule of thumb, the strut or compression stress field between the support and the first connector is at an angle with the axis of the beam of less than 60 degrees.

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