Currently Timber-Concrete Composite (TCC) Constructions are often applied for strengthening existing timber beam slabs. The load bearing capacity of the composite construction is primarily affected by the material properties of the timber beam and the concrete slab. But the type of bond between both parts is also of high importance. The concrete slab has to perform several tasks, not only in load carrying direction of the ceiling but also perpendicular to the direction of span or for stiffening the whole building. These tasks will be pointed out in this paper. Furthermore the working process (easy workable mixture and exchange of conventional reinforcement) and the dead load of the construction are of particular interest in the field of redevelopment. Several innovative concretes have been verified for the use in TCC constructions. Regarding their fresh and hardened concrete properties, they all can be described as High Performance Concretes (HPC). In this paper Self Compacting Concrete (SCC), Fiber Reinforced Concrete (FRC), Structural Lightweight Concrete (SLWC), High Strength Concrete (HSC) or combinations of them will be focused. Especially the advantages but also the disadvantages of innovative concretes for the use in TCC will be presented as well as the results of some experimental investigations.

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Regarding the redevelopment of existing residential buildings the timber-concrete-compo- site (TCC) construction is an innovative possibility to toughen up timber beam ceilings. Thereby a concrete slab is added to the timber beams. Both parts of the construction are connected by using special shear connectors. In this case timber is mainly loaded in tension and concrete is generally loaded in compression. The bearing capacity as well as the serviceability of the ceiling can be improved by this composite construction. The idea of combining the construction materials timber and concrete in the way that they both can take and carry on loads is not new. In Germany it was mentioned in 1939 for the first time. The cityscape of Central European towns is mainly characterized by buildings constructed before the 50th of the last century. The protection of the historical main structure of these buildings is getting more important today. Floors built up till that time were primarily made of timber. Research in Germany has been intensified during the last decade. This paper will show the specific properties of timber-concrete composite floors. Several metallic combing agents exist currently. Type and distance of the connection members influence the load bearing behavior of the composite construction. The main types used in Germany will be presented in this paper. The possible ways of calculating timber-concrete composite ceilings will be given and the design basis will be explained.

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The idea to combine the building materials timber and concrete is well known since the 20th of the last century. While timber is beneficial in bearing tensile forces, concrete on the contrary sustains compressive forces very well. Thus, connecting both materials in the way that loads can be transferred between them, their advantages can be used to improve the load bearing capacity of structures. A lot of researches were carried out to investigate different problems of timber-concrete composite (TCC) constructions during the last years. Yeoh et al. [1] for example gave an overview of different full-scale short-term collapse tests in order to evaluate the load bearing behavior of different TCC systems. Nevertheless, some questions are still very few explored, among them is the lateral load bearing behavior of TCC constructions. These structures can be considered as 3 dimensional plane structures, being able to distribute loads along and perpendicular to the span of the timber beams. A concentrated load (applied to one beam of the TCC construction) will deflect it due to bending. All beams are connected with each other because of the concrete slab. For this reason adjacent beams also deflect even if no loads are applied to them directly. These beams contribute to the load bearing of the loaded beam and relieve it partly from the loads, reducing stress in this beam. The described behavior, of distributing loads perpendicular to the span, is called lateral load bearing behavior. This paper will report on short-term bending testes of TCC slabs, carried out at Leipzig University of Applied Sciences. Several slabs have been tested. Each of them had a span of 3.9 m, consisting of three timber beams (10/20 cm) and a connecting concrete slab (thickness 6 cm). Only the middle beam was loaded in the third part points. During the test deflections, as well as strains, at different points were recorded. Additionally, the concrete properties were determined and push out tests were carried out. Overall, seven TCC slabs were manufactured and tested. With the slabs several parameters have been varied, e.g. the type of concrete, the stiffness of the connection system, and the center distance of the timber beams. By varying these three parameters, their effect on the lateral load distribution was examined by measuring deflection and strain at different points of the composite slab. A timber beam ceiling, as reference sample, without concrete topping was tested additionally. The experiments and its results will be described in detail in the paper.