Keywords: structural analysis, composite materials and structures, material models, materials characterisation, finite element analysis, concrete, timber, connections.

The study of the state-of-the-art of the timber-concrete structures [1,2] reveals a great potential of this constructive technique to be explored, with structural applications in the urban environment as well as in the agricultural one. Besides the structural performance, this solution provides excellent architectural effect due to the contrast between the timber and the concrete pieces used in the execution of panels of walls, covering and floor slabs for the different modalities of new constructions and/or reforms. The mechanical performance of a composite structure is due, in general, to the efficiency of the connection system that can be of the rigid or semi-rigid type.

This system must assure the interaction between concrete and timber transmitting, in this way, shear stress efforts in the contact interface and, also, impede the vertical slip between the two materials. With the intention to contribute for the spread of the use of timber-concrete structures [3], this research approaches these two types of the connections, with more emphasis in the metallic flexible systems (nails and screws). In this way, it is evaluated the mechanical performance of tested timber-concrete structures such as T beams (dimensions: 20cm 30 cm) and prototypes of panels (dimensions: 80 cm 300cm). It was used in these structures pieces of the Goupia glabra, a Brazilian wood species.

The analysis of the mechanical behavior of these composite structures is based on the principle of the equilibrium of forces and on the compatibility of displacements, verified by means of differential equations of fourth order and by the Finite Element Method, through the use of the SAP2000 software [4]. Examples of verification and design of structures are presented to fit to the conditions of design safety [5], in the ultimate and serviceability limit state. Through the analysis of the obtained results in the theoretical, the numerical and the experimental procedures, the most important conclusions can be summarized as follows:

• the mathematical model of design developed from the equilibrium of the forces and the compatibility of displacements and the numerical model based on Finite Elements Methods following the SAP software [4] presented results close to the experimental ones.
• the mechanical behaviour of the connection system through the slip modulus can be considered satisfactory.
• the consideration of the effect of non-linearity of the material is important for the model implemented in the Mathematica software [6].
• from the experimental results of the three panels for load levels that correspond to the serviceability limit state values, the increase of the effective connection area had little relevance for the reduction of the vertical displacements.
• the connection system for nails revealed a satisfactory efficiency, besides providing to greater easiness for its installation in the timber parts, and commercial cost for unit is lesser than other usual connectors.

In view of the theoretical-experimental results obtained in this work, it can be concluded that timber-concrete composite structures have favourable horizon of applications in civil constructions and it is of basic importance the incentive and the continuity of the development of this constructive technique [7] in the technical and scientific community.

1

Ceccotti, A., "Timber-concrete composite structures", Timber Engineering STEP/EUROFORTECH, Vol 2, Almere: Centrum Hout, E13, pp.1-12, 1995.

2

Stevanovic, B., "Elastically coupled timber-concrete beams", Proceedings of the International Wood Engineering Conference, Vol 3, New Orleans, 425-430, 1996.

3

European Committee for Standardization (CEN), "European Prestandard ENV 1993. Eurocode 5: Design of timber structures", European Committee for Standardization, Brussels, 1993.

4

SAP2000, Ver. 7.0, Berkeley, California: Computers and Structures, Inc.

5

Brazilian Association Of Technical Codes, NBR6118: Concrete Structure Design, Rio de Janeiro, (In portuguese), 1982.

6

Mathematica, Version: 3.0, Champaign, Il: Wolfram Research, Inc.

7

Brazilian Association Of Technical Codes, NBR7190: Timber Structure Design, Rio de Janeiro, (In portuguese), 1997.

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