Composite slab floors made of cross laminated timber and ultra high-performance concrete: Early-age deflection, stripping time, and its implication on the structural performances

•The short-term deflection of the CLT-UHPC floor without shoring reached 50 % of the maximum allowed.•UHPC shrinkage causes 75 % of the short-term deflection.•UHPC shrinkage reduced the effective bending stiffness of 35 %.•A discretized solution based the effective modulus has been developed to predict the short-term deflection.•The developed analytical model allows estimating the optimal stripping time.•CLT-UHPC floor of 10 m with a shoring removal time 2 days after casting can be designed. Timber-Concrete Composite floors made of Cross-Laminated Timber (CLT) and Ultra-High-Performance Concrete (UHPC) boast remarkable efficiency in lightweight and slenderness. While the rapid UHPC hardening facilitates swift construction, the optimal shoring time depends on the effect of the UHPC autogenous shrinkage on the floor deflection. This study aims to investigate the experimental deflection of CLT-UHPC floors at an early age without shoring and to develop a simplified model for predicting the optimal shoring time for TCC floors. An eco-friendly UHPC with recycled glass waste is considered in this study. Firstly, the evolution of its modulus of elasticity and compressive strength as well as the early-age shrinkage were experimentally characterized. Furthermore, the shear behavior of the notch connection was evaluated after 28 days, and it was estimated to be proportional to the stiffness of the concrete at an early age. Then, two TCC floors made of CLT-UHPC with a span of 3.6 m were cast and their deflection under the self-weight of fresh concrete was measured over the initial 28-day period in a simple supported configuration without the use of shoring. A simplified analytical model was developed to predict the TCC deflection at an early age by coupling an existing solution with the concept of Age-Adjusted Effective Modulus (AAEM). The model effectively predicted the experimental early-age deflection of the CLT-UHPC floor without the use of shoring. Finally, after 3 months, the TCC floors were tested under bending, showing a reduced structural stiffness of about 35 %, caused by concrete cracking due to restrained shrinkage. The parametric analysis with the developed analytical tool allowed for estimating the maximum span of CLT-UHPC floors without shoring or, for longer spans, the optimal time of shoring removal. This study offers valuable insights into the behavior of CLT-UHPC along, along with a robust analytical tool to optimize their design and construction of