Design and mechanical behavior of precast bottom slabs with innovative additional double channel steel stiffeners

Abstract In recent years, composite slabs have been extensively adopted in diverse structural systems owing to their superior construction efficiency, exceptional structural integrity, as well as reliable fabrication with consistent quality assurance. Compared to traditional cast‐in‐place slabs, precast slabs require notably less formwork. However, due to the insufficient out‐of‐plane stiffness of precast slabs, the fabrication of conventional composite slabs still relies heavily on bottom support systems, a process that is both labor‐intensive and time‐consuming. To address the aforementioned issues, a novel type of reusable additional double channel steel stiffener (ADCSS) is proposed to temporarily enhance the out‐of‐plane stiffness and crack resistance of precast bottom slabs during the lifting, transportation, and construction stages. The ADCSSs are installed beneath the slabs and are effectively connected to the slabs by specially designed spring connection joints. Based on the bending mechanism of unbonded composite beams, this study proposes a comprehensive stiffness‐based design method for the ADCSS. To verify the reliability of the proposed design method and the effectiveness of the ADCSSs, three full‐scale precast bottom slabs equipped with ADCSSs were fabricated and tested. Under construction loads, the mid‐span deflections of the three specimens did not exceed l /200 (9.5 mm for OBS‐1 and 14.5 mm for PBS‐1 and PBS‐2, respectively), all below the allowable limit. The maximum difference between the measured and theoretical cracking loads was less than 13%, confirming the validity of the design approach and the satisfactory performance of the ADCSSs during the construction stage. A refined finite element model was developed using ABAQUS software to systematically investigate the failure mode of the precast bottom slabs with ADCSSs. It was also used to examine the influence of various parameters, including flange width, thickness, and the cross‐sectional height of the channel steel, on the stiffness and load‐carrying capacity of these precast bottom slabs. The results demonstrate that the proposed innovative ADCSS not only enables precast bottom slabs to meet the requirements of load‐carrying capacity and crack control, but also offers significant advantages in production, transportation, and construction stages.