Push-out tests on steel collar connection for composite timber-concrete beams

The paper deals with the experimental analysis of an innovative and reversible connection system for timber-steel-concrete floor beams. The connector between the timber beam and the concrete slab consists of a steel collar which is composed by two parts, bolted together at appropriate folded wings. The superior ones have the function of connectors and are immersed in the concrete cast. A layer of rubber is interposed between the sleeve and the wooden beam, in order to assure the adaptability of the system to the irregular surface of the existing ancient beams. The friction at the wood-steel surface is guaranteed by the bolt tightening force. In this paper monotonic push-out tests on several circular shaped configurations of the study system are presented, they being part of a more comprehensive experimental campaign, aimed at the system performance evaluation and optimization. Different types of connector, which correspond to further improvement of the system, are studied, pointing out the following aspects: the evaluation of the system failure mechanism; the optimization of the wood-rubber-steel contacts; the system improvements due to the bolts tightening increment. The connection behaviour is discussed in terms of force-relative slip relationship.