## 5 Conclusions  
When a composite PC beam is used in a member with a long span or a large live load, the shear force and the bending moment increase, and the horizontal shear stress acts on the interface within the moment inflection point. In particular, a continuous composite PC beam can exhibit a larger rate of change in the negative moment compared to the length of the moment inflection point. On the other hand, the horizontal interface of the composite PC beam is located in the tensile region or the compression region of the cross-section depending on the negative moment or the positive moment. When designing continuous PC composite beams, the horizontal shear performance may be expected to vary depending on the location of the interface. This study examined whether the horizontal shear design equations properly evaluate the conditions of the interfaces, such as interface locations, surface roughness, and clamping stresses of shear connectors. A database was constructed for 84 push-off experiments and 95 beam flexure tests from previous studies. The adequacy of the design criteria was evaluated through statistical analyses comparing the results of experimental database with ACI, PCI, AASHTO LRFD, and MC 2010 design criteria. The conclusions from this study are as follows.  
1. It was found that the horizontal shear strength equations of the current design codes predict conservatively the horizontal shear strength of push-off specimens regardless of the variables such as the concrete compressive strength and the clamping stress of the shear connector on the interface, as well as surface roughness. However, the push-off tests cannot distinguish the difference from the interface location for either C-type or T-type.
2. The horizontal shear strengths by flexure tests were shown to vary greatly depending on the location of the interfaces. In particular, composite beams with roughened T-type interfaces showed a distribution of strength ratios with a minimum value of 0.41 to 0.67 and an average value of 0.77 to 1.15, indicating that horizontal shear strengths are overestimated.
3. The horizontal shear strength of the composite beam with roughened T-type interface increased as the compressive strength of concrete increased, but decreased as the clamping stress increased. Based on evaluation, it could be suggested that the shear connector did not operate sufficiently to control the slip deformation at the interface.
4. In order to prevent members with roughened T-type interface from brittle failure, it is recommended to use a friction coefficient of 0.7 when using the shear friction method of ACI code.  
Figure 13: C-type interface for beam specimens with roughened surface.  
* It is necessary in the future studies to include the interface location with respect to the neutral axis of composite beam as a variable for the interface shear design equation.  
Original draft manuscript and investigation, Y.-H.O.; validation and review writing J.-H.M. Both authors have read and agreed to the published version of the manuscript.  
This research was supported by the Konyang University Research Fund in 2019 (Grant No. 2019A0022).  
Not applicable.  
The data presented in this study are available on request from the author.  
The authors declare no conflict of interest.