## 4 Conclusions  
In this study, an experimental investigation was performed on the structural performance of the steel pile cap strengthened with the proposed perfobond connectors under lateral loading. A bending test was conducted on seven specimens by considering the type of perfobond shear connectors, infilled concrete depth, and the number of L-shaped steel plates as test parameters. The failure characteristics of the test specimens were examined, and their load-displacement curves were analyzed. The main conclusions of this paper are as follows:  
1. All of the test specimens basically showed very similar crack propagation patterns. Cracking first occurred on top of the concrete block in the direction perpendicular to the lateral load and then propagated into its side surfaces. As the load further increased, cracks in the direction parallel to the lateral load appeared on top of the concrete block, and concrete crushing occurred on its compression side.
2. In all of the test specimens, where the proposed perfobond shear connectors were installed, the crack pattern of a half circle shape was observed on top of the concrete block. In contrast, this phenomenon was not observed in the reference specimen, where the steel pile was strengthened with conventional steel rebars.
3. The specimens strengthened with the open-hole type perfobond connectors have almost the same bending resistance capacity as the reference specimen although the concrete infilled depths of the former are only in the range of approximately 29%-57% of the latter. Furthermore, their initial stiffness is almost equal to that of the reference specimen, and they also retain a level of ductility comparable to that of the reference specimen. The advantage of the proposed perfobond connectors mainly lies in its enhanced constructability although they did not show a significantly greater improvement in structural performance than the conventional rebar strengthening method.
4. The open-hole type perfobond specimens have approximately 10%-20% higher bending resistance capacity than those with closed-hole type perfobond connectors. The increase of peak strength due to increasing concrete infilled depth is more pronounced with closed-hole type perfobond specimens.
5. The number of L-shaped plates does not have a high impact on the bending resistance capacity of the specimen; thus, it may be impossible to install any of the L-shaped plates with the proposed perfobond shear connectors.  
**Acknowledgments:** The corresponding author of this paper acknowledges support from the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (Grant number: 2013R1A1A1076011).  
**Author Contributions:** In this paper, [PERSON] proposed the main concept of the new perfobond shear connector and prepared the experimental program to investigate its structural performance when subjected to lateral loading; [PERSON] made a contribution to the implementation of the experimental program and discussed the test results; [PERSON] provided a suggestion on the overall organization of the paper and prepared the tables and figures included in the paper; [PERSON] provided the interpretation of the test results and wrote the entire manuscript.