Lateral Load Bearing Behavior of Timber-Concrete Composite Constructions

Abstract

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.