ABSTRACT
ABSTRACT: Timber/concrete-composite systems are efficient and economical structures to reinforce timber ceilings. Novel non-linear finite element models enable reliable structural analyses of this class of constructions. Comparisons of finite element simulations and experimental results show the suitability of the numerical models to simulate the load-bearing behavior and long-term features (see Schmidt et al. 2002a, 2003a, 2003b). The design of timber/concrete composite beams is currently carried out according to DIN 1052 and EC 5, respectively, based on linearly calculated internal forces (approximated by so-called γ -procedure). However, the real load-bearing behavior shows considerable non-linearities. For this reason and because of simplifications of the γ -procedure, the safety zone between working load and failure load is not constant depending on the system parameters like the load-bearing behavior of the joints. A comparison between failure loads determined by finite element analysis and the working loads according to the current design rules will be shown. The influence of the non-linear behavior of the connectors on the load-bearing behavior of the composite beams is important. It is shown that the decrease of load-bearing capacity is smaller than assumed by current code of practice. Structures with different spacing of connections have the largest safety-factor (see Schmidt et al. 2004). These systems can be designed more economically. As result of the investigations, a new design proposal is presented, which takes nonlinearities into account and guarantees a constant safety-zone between failure load and working load. This proposal permits an economical design of timber/concrete composite beams.
