# Shear Resistance Assessment of the Y-Type Perfobond Rib Shear Connector under Repeated Loadings
## 6 Conclusions  
This study investigated the residual shear resistances after one-directional repeated loads on the Y-type perfobond rib shear connectors. The development procedure for a design formula was proposed to provide a design residual shear strength according to the properly selected target reliability level. The conclusions are as follows:  
1. The design residual shear resistance formula under repeated loads was proposed with a resistance (reduction) factor, which can be selected depending on the target reliability level under the repeated load environments. The various reduction factors were provided for the range of target reliability index from 2.0 to 3.0. The proposed procedure can be applied to the other Y-type perfobond rib shear connectors with different design variables and repeated load intensities such as different Y-rib sizes, rebars, concrete strengths, etc.
2. The residual shear strength of Y-type perfobond rib shear connectors was found to decrease linearly with cumulated energy dissipation due to the repeated loads. The decreasing rate was evaluated to be quite stable with \(2\times 10^{-5}\). The nominal residual shear strength can be estimated from the residual shear strength factor and the nominal shear strength. The residual shear strength factor was estimated by empirical data from the monotonic loading tests on the various specimens that have experienced various repeated loads.
3. It was found that the energy dissipation per each repeated load converges after 5-10 repetitions when the load intensity is up to 65% of the ultimate shear strength. However, the repeated load intensities over 65% of the ultimate shear strength generate scattered energy dissipations. It was also found that the residual slip increment due to repeated load does not become stable when the repeated load intensity exceeds 55% of the ultimate shear resistance.
4. From the load-strain relationships on the Y-ribs and rebars, it was found that Y-ribs contribute mainly to the shear resistance when the load is below 55% of the ultimate shear strength.
5. The residual ductility of Y-type perfobond rib shear connector remains intact after the repeated loads, given that the intensity of the repeated loads does not exceed 65% of the ultimate shear strength.  
Conceptualization, methodology, writing--review, S.-H.K.; formal analysis, O.H., S.Y. and T.B.; specimen and experiment, O.H., S.Y. and T.B.; writing--draft preparation, O.H.; All authors have read and agreed to the published version of the manuscript.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Number of Repeated Loads (\(n_{L}\))** & \(\beta\) & **785 kN** & **1010 kN** & **1235 kN** & **1460 kN** \\ \hline
25 & 2.0 & 0.846 & 0.845 & 0.838 & 0.832 \\  & 2.5 & 0.773 & 0.772 & 0.763 & 0.755 \\  & 3.0 & 0.700 & 0.699 & 0.689 & 0.678 \\ \hline
50 & 2.0 & 0.844 & 0.837 & 0.809 & 0.771 \\  & 2.5 & 0.771 & 0.762 & 0.715 & 0.654 \\  & 3.0 & 0.697 & 0.687 & 0.608 & 0.497 \\ \hline
100 & 2.0 & 0.834 & 0.802 & 0.646 & 0.475 \\  & 2.5 & 0.759 & 0.704 & 0.427 & 0.157 \\  & 3.0 & 0.683 & 0.586 & 0.118 & - \\ \hline \hline \end{tabular}
\end{table}
Table 24: Reduction factor for design residual shear strength (\(\phi_{r}\)).  
**Funding:** This work was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry & Energy (MOTIE) of the Republic of Korea (No. 20194030202460).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Conflicts of Interest:** The authors declare no conflict of interest.