# Numerical Study on the Bending Performance of Steel-Ribbed Composite Slabs for Substations
## 6 Conclusions  
This study examines the unidirectional and bidirectional bending performance of prestressed concrete composite slabs with steel ribs for substation applications. The following conclusions are drawn:  
1. For unidirectional bending performance, the designed composite slabs present typical two-stage load-bearing characteristics, with concrete cracking as the turning point. The post-crack stiffness of the composite slabs remains relatively stable until failure. The cracks on the bottom surface are predominantly transverse and uniformly distributed from mid-span toward the supports, with localized cracks along the steel ribs. The ultimate capacity of the slab depends on the yielding of the prestressing steel. The numerical simulation results align closely with theoretical calculations, with errors within 7.76%, thereby validating the accuracy of the FE models.
2. For bidirectional bending performance, the loading behavior of the composite and monolithic slabs can be categorized into five distinct stages: the decompression state, elastic state, incipient cracking state, diagonal cracking state, and fully cracked state. All the slabs demonstrate comparable stiffness prior to cracking and similar crack distributions at failure, with a checkerboard pattern near the mid-span and extending  
Figure 23: Parametric analysis results of the triple-spliced composite slab: (**a**) Concrete strength; (**b**) Ratio of the longitudinal prestressing steel; (**c**) Strength of the joint-connecting rebar; (**d**) Diameter of the joint-connecting rebar.  
diagonally toward the slab corners. The presence of splicing joints reduces the post-crack stiffness slightly and increases the ultimate deflections of the double-spliced and triple-spliced composite slabs, which are 7.53% and 7.75% greater than that of the monolithic slab, respectively. Nonetheless, the ultimate capacities remain close to that of the cast-in-place slab.
3. The parametric analysis shows that the longitudinal prestressing steel ratio has the most significant effect on the behavior of the bidirectional slab, with the ultimate bearing capacity increasing in proportion to the prestressing steel ratio from 0.072% to 0.394%. The beneficial effect of the increase in concrete strength on the bearing capacity gradually decreases, especially after C40. When the arrangement of the joint-connecting rebars greater than C4 @ 200 mm with a minimum yield strength of 235 MPa, the transversal force transfer across the joints is reliable.
4. The new type of prestressed concrete composite slabs with steel ribs introduced in this study features high cracking strength, stiffness, load-bearing capacity, and commendable ductility under both unidirectional and bidirectional loading conditions, making it highly appropriate for substation applications. For different substation sizes, the ratio of the prestressing steel should be adjusted to meet the capacity requirements. For a larger room space, a grid of secondary beams can be set beneath the floor slabs to form a two-way slab system to obtain a higher bending performance.  
Conceptualization, methodology, and writing--original draft preparation, L.L. and Y.L.; investigation and formal analysis, Z.W. and Y.J.; software and data curation, H.C.; supervision and writing--review and editing, Y.Z.; validation, C.L.; resources and project administration, K.R. and L.T. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
The datasets generated and/or analyzed during the current study are available from the corresponding author upon reasonable request.  
Authors [PERSON], [PERSON], [PERSON], and [PERSON] were employed by Shandong Electric Power Engineering Consulting Institute Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.