Flexural behavior of precast concrete sandwich floor with innovative hybrid slab joint connections

Slab joint connections have a critical impact on the vertical bearing capacity, vertical vibration comfort, in-plane stiffness, and seismic performance of multi-story and high-rise buildings adopting precast concrete (PC) floor systems. An innovative hybrid slab joint connection (SJC) is proposed for improved discretely connected precast concrete floor (DCPCF-m) to enhance the mechanical performance and production efficiency of untopped PC floor systems. Furthermore, the DCPCF-m employs a PC sandwich floor that markedly reduces the material use and the self-weight of floor system. Vertical uniform loading tests were conducted on five full-scale DCPCF-m specimens and two cast-in-place specimens to investigate the force transmission mechanism of the new hybrid SJC and its influence on the flexural behavior of the DCPCF-m in the orthogonal slab laying (OSL) direction. The results revealed that the innovative hybrid SJC design significantly enhanced the flexural behavior of the floor system. By allocating the hybrid SJC away from the mid-span and providing an adequate number of paired connectors in each hybrid SJC, unfavorable side effects could be avoided. Based on the variable cross-section beam, a simplified theoretical method for the calculation of the equivalent flexural stiffness comprehensively considering the influence of hybrid SJC on the effective width of PC slabs, equivalent flexural stiffness of hybrid SJC, and shear lag effect was proposed for DCPCF-m in the OSL direction. Compared with the experimental result, the error was generally within 13 %, indicating that the theoretical method could better predict the equivalent flexural stiffness. This study could provide a reference for the design and application of untopped PC floor systems.