# Shear Behavior of Concrete Encased Steel Truss Composite Girders
## 4 Conclusions  
In this study, tests using truss type and presence of stirrups as variables were performed to verify the shear performance of EST composite girders. Subsequently, based on the crack patterns and failure modes observed from the tests, the behavioral characteristics of the EST composite girder were analyzed in detail. The following conclusions were obtained from this study:  
1. It was discovered that in the P specimen series applied with the Pratt truss, horizontal shear cracks that occurred along the top chord governed the shear behavior of the member. In addition, the shear strength calculation method considering the horizontal  
Figure 11: Freebody diagram at truss connection.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Specimen** & \(V_{test}\)1  & \(V_{sr}\)1  (kN) & \(V_{test}\)/\(V_{sr}\) & **Failure Mode** \\ \hline WV & 659.5 & 655.3 & 1.01 & Diagonal shear failure \\ \hline W & 661.9 & 515.8 & 1.28 & Diagonal shear failure \\ \hline \hline \end{tabular}
\end{table}
Table 5: Comparison of test and analysis results on W specimen series.  
shear failure surface provided relatively accurate and conservative results for the shear strength of the P specimen series.
2. In the W specimen series applied with the Warren truss, the diagonal web member failed to contribute effectively to the shear resistance mechanism of the member. This was because the screw rod exhibited shear failure at the EST node area before the diagonal web member reached its yield strength. Meanwhile, it was discovered that the shear strength calculation method considering the shear failure of the screw rod predicted the shear strength of the W specimen series reasonably well.
3. Horizontal shear failure was one of the main failure modes of encased composite girders, and a very brittle failure may occur in the entire member when the screw rod exhibits shear failure prior to the yielding of the diagonal web member. Therefore, these aspects should be considered when designing an EST composite girder.
4. Some of the shear behavior characteristics of EST composite girders were identified in this study. However, the EST composite girders fabricated in this study did not necessarily exhibit a desirable failure mode. Hence, it is predicted that if the shear failure strength of the screw rod and the horizontal shear strength presented in this study are considered in the design process, then undesirable failure modes can be avoided.
5. There could be a stress concentration at truss nodes, which caused a brittle shear failure of the screw rod. Therefore, a finite element analysis is recommended as a future research work to identify the stress concentration phenomenon. In addition, because the EST composite girder system was designed to allow the beam-column to be continuous in the negative moment region, additional investigations regarding the seismic performance of the EST girder-column connection should be conducted.  
Original draft manuscript, C.L.; validation, S.-H.C. and S.-J.H.; investigation, J.Y.O. and M.-S.L.; supervision and review writing, K.S.K. All authors have read and agreed to the published version of the manuscript.  
This research was supported by Mid-career Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2019R1A2C2086388). The authors also would like to express sincere thanks to Hi Structural Engineers Co. for financial support and assistance on this research project.  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
The authors declare no conflict of interest.