Structural Behaviour of CLT Floor Systems in Hybrid Timber Buildings
Shrinkage-Induced Restraint Forces and the Influence of Diaphragm Stiffness on Stability Response
F.C. Bon (TU Delft - Civil Engineering & Geosciences)
G.J.P. Ravenshorst – Graduation committee member (TU Delft - Bio-based Structures & Materials)
J.W.G. van de Kuilen – Graduation committee member (TU Delft - Bio-based Structures & Materials)
H.R. Schipper – Graduation committee member (TU Delft - Applied Mechanics)
Niels Castelein – Graduation committee member (Sweco)
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Abstract
This thesis investigates the structural behaviour of cross-laminated timber (CLT) floor systems in hybrid concrete core–timber frame buildings, with a focus on shrinkage-induced restraint forces and the influence of diaphragm stiffness on global stability.
CLT floor panels act as diaphragms transferring horizontal loads to the concrete core, while simultaneously undergoing moisture-driven shrinkage after installation. When restrained, this shrinkage induces additional forces in connections, which are governed by both material behaviour and connection stiffness. At the same time, these connections determine the in-plane stiffness of the floor diaphragm, directly affecting the global structural response.
The study combines analytical and numerical approaches. First, moisture-driven shrinkage and viscoelastic stress relaxation in CLT are evaluated, showing that long-term stresses are strongly reduced compared to purely elastic predictions. Second, analytical models are developed to quantify shrinkage-induced forces in representative connection configurations, identifying panel length, installation moisture content, and connection stiffness as key governing parameters. Finally, a case study using finite element modelling demonstrates how variations in diaphragm stiffness influence global stability, displacement response, and the relevance of second-order (geometrically non-linear) effects.
The results highlight a fundamental design trade-off: increasing connection stiffness improves structural stability but leads to higher shrinkage-induced forces, whereas more flexible detailing reduces these forces at the expense of diaphragm stiffness. The findings provide practical insight into the interaction between material behaviour, connection design, and global system response, and support more informed design decisions in hybrid timber buildings.