Creep Behavior of Timber Concrete Composite Connections for Demounting and Reuse

Sammanfattning

Demountable timber-concrete composite (TCC) connections offer significant potential for circular material flows and sustainable construction by enabling disassembly, reuse, and recycling of structural elements. In particular, dry-dry connections between prefabricated concrete and cross-laminated timber (CLT) elements may reduce construction waste and improve resource efficiency. However, the time-dependent behaviour (creep) of demountable threaded-rod connectors remains insufficiently understood, especially for connectors passing through the full composite section. This study investigates the embedment creep behaviour of threaded-rod connections in timber and concrete and integrates the experimental findings into an extended beam-on-foundation (BoF) framework for modelling the long-term response of demountable TCC connections. Experimental embedment creep tests were conducted on 24 timber specimens loaded parallel and perpendicular to the grain, as well as on 12 prefabricated concrete specimens, both reinforced and un-reinforced. The tests consisted of SLS cyclic loading followed by sustained loading for creep measurements over approximately 24 hours. The measured embedment deformations were evaluated using power-law creep formulations, which were subsequently implemented in both analytical and numerical BoF models based on an extension of Kuenzi's beam-on-foundation approach. The developed models were used to predict the time-dependent response of the demountable connection and were validated against independent connection tests reported in the literature. The results show that the power-law formulation provides a satisfactory representation of the viscoelastic embedment behaviour of both timber and concrete. Furthermore, the extended BoF framework successfully captured the redistribution of stresses and the time-dependent deformation behaviour within the connection. Good agreement was observed between the analytical and numerical modelling approaches, although both models predicted larger connection displacements than those measured experimentally, indicating possible stiffness underestimation. Despite the relatively short experimental duration, clear creep effects were identified. The study demonstrates the potential of combining experimentally derived creep laws with beam-on-foundation modelling for predicting the long-term behaviour of demountable TCC connections, while highlighting the need for further long-term experimental validation.