## 6 Conclusions  
In this study, prefabricated composite girders with different girder-to-deck connections were proposed, and the structural performance of prefabricated composite girders was investigated. From the results, the conclusions below were drawn:  
1. Several different types of girder-to-deck interface connections for the prefabricated composite girder, which have a sufficient structural performance compared to the AASHTO LRFD requirements, can be proposed by rationally arranging shear reinforcement at the connection detail based on the application of interface shear transfer theory. Along with that is the change of study connector height and precast deck structure.  
Figure 19: Mises stress of reinforcement connectors at failure-mode shape (Case 1a).  
Figure 18: The moment ratio-displacement curve for cases of the parametric study.  
2. The details of the girder-to-deck interface connections are different so the reinforcement spacing of the cases varies. The spacing between bars of reinforcement connecting the precast deck and the grout which controls the connection design increased gradually from Case 01 to Case 04. However, the reinforcement spacing can be adjusted for specific design purposes based on influential parameters. With such design of reinforcement spacing, all developed cases satisfied the interface shear criteria according to both conventional and plastic approaches.
3. There was no significant difference in flexural moment strength between the investigated cases. In all cases, the flexural performance was ensured. The influence of the degree of interaction between the connection grout and precast concrete deck was negligible, since the condition of the full shear connection was satisfied in all cases for the prefabricated composite girder and reinforcement spacing should be optimally designed through the theory of interface shear transfer.
4. The AASHTO LRFD provision of interface shear transfer is applied to concrete-to-concrete interfaces. However, the FEA results are in good agreement with the calculation results according to the AASHTO LRFD. It demonstrates that the AASHTO LRFD provision of interface shear transfer is applicable to grout-connection interfaces, in particular, girder-to-deck interface connections of prefabricated composite girders. A Push-off test needs to be carried out for verification.
5. All developed cases can be used for railway bridges. If the influential parameters can be adjusted to arrange the reasonable reinforcement spacing, Case 01 is the most optimum case that should be considered. In contrast, other cases should be considered.  
Conceptualization, B.H.C.; methodology, B.H.C., H.T.D. and J.M.; software, H.T.D.; validation, B.H.C.; formal analysis, H.T.D. and B.H.C.; investigation, H.T.D., B.H.C. and J.M.; resources, B.H.C.; data curation, B.H.C. and J.M.; writing--original draft preparation, H.T.D.; writing--review and editing, B.H.C. and J.M.; visualization, J.M.; supervision, B.H.C.; project administration, B.H.C.; funding acquisition, B.H.C. All authors have read and agreed to the published version of the manuscript.  
This research was conducted with the support of the \"National R&D Project for Smart Construction Technology (Grant No.22 SMIP-A158708-03)\", funded by the Korea Agency for Infrastructure Technology Advancement under the Ministry of Land, Infrastructure and Transport, and managed by the Korea Expressway Corporation.  
Not applicable.  
The authors declare no conflict of interest.