# Flexural Capacity of a New Composite Beam with Concrete-Infilled Tubular Lower Flange
## 5 Conclusions  
In this study, we proposed a new steel concrete composite beam that has a similar shape to the conventional steel wide flange beam, but whose lower flange has a tubular shape with infilled concrete. The bending capacity of the new composite beam was investigated by performing a two-point loading test on seven specimens, which can be categorized mainly into two types, non-composite and fully  
Figure 16: Ultimate failure modes of the fully composite specimens: (**a**) 738-WFC-X-X-TD; (**b**) 585-TFC-O-R1-DD.  
Figure 17: Measured strain distributions of the fully composite specimens: (**a**) 738-WFC-X-X-TD; (**b**) 585-TFC-O-R1-DD.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Specimen**} & \multicolumn{2}{c}{**Location of Neutral Axis at Failure (mm)**} & \multirow{2}{*}{**Ratio of (2) to (1) (\%)**} \\ \cline{2-3}  & **Theory (1)** & **Test (2)** & \\ \hline
738-WFC-X-X-TD & 154.9 & 152.6 & 98.5 \\
585-TFC-O-R1-DD & 98.8 & 166.3 & 168.3 \\ \hline \hline \end{tabular}
\end{table}
Table 13: Locations of neutral axis at failure of the fully composite specimens.  
composite specimens. The load versus displacement curves were plotted for all the specimens and their failure modes were identified. Theoretical equations to estimate the flexural strengths of the new composite beam members were proposed and their accuracy was examined by comparing the predictions of the equations with the test results. The main conclusions of this paper are as follows:  
1. The proposed composite beam with lower tubular flange can have almost equal flexural strength to that of a composite beam with a conventional wide flange at the fully composite stage, although the latter has an almost 26% higher total depth. Consequently, the proposed composite beam is highly effective in reducing the floor height.
2. The nominal flexural strength of the proposed composite beam at fully composite stage can be determined based on its plastic moment. The theoretical estimations based on this assumption predicted the experimental results well.
3. The nominal flexural strength of the proposed composite beam at the construction stage can be determined based on its yield moment since its ultimate failure mode was generally local web buckling. However, if it does not have any openings in the web, its plastic moment can be taken as the nominal flexural strength, and it is highly resistant to lateral torsional buckling due to the existence of the lower tubular flange.  
The first author of this paper acknowledges support from NI Steel Co., Ltd. and the Basic Science Research Program through the National Research Foundation of Korea (Grant Number: NRF-2016 R1D1A1B01010615).  
In this paper, [PERSON] and [PERSON] proposed the main concept of the new composite beam; [PERSON] prepared the experimental program to investigate its flexural capacity and made a contribution to the implementation of the experimental program. [PERSON] analyzed the test results and prepared the tables and figures included in the paper; [PERSON] derived all of the theoretical flexural strength equations of the new composite beam and wrote the entire manuscript.  
The authors declare no conflict of interest.