# Flexural Capacity of a New Composite Beam with Concrete-Infilled Tubular Lower Flange
## 4 Test Results and Discussion  
### Non-Composite Specimens  
Table 10 summarizes the flexural strengths of the five non-composite specimens by the theoretical estimation and test and their ultimate failure modes. Their nominal flexural strengths are estimated using the strength equations provided in Section 3.1. In order to take into account the effect of the self-weight of the specimens on the test results, the adjusted nominal flexural strengths are calculated by subtracting the moment by the self-weight from the nominal flexural strengths. These are in turn compared with the maximum moments obtained from the test results, and the ratios of the latter to the former are also provided in the table. In Figure 12, the load versus displacement curves of the five specimens are presented, and the peak load point of each curve is represented by an empty circle. The photos showing the ultimate failure mode of each specimen are given in Figure 13. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Specimen**} & \multicolumn{3}{c}{**Theoretical Estimation (kN-m)**} & \multicolumn{3}{c}{**Test Results (kN-m)**} \\ \cline{2-6}  & \begin{tabular}{c} **Nominal** \\ **Flexural** \\ **Strength** \\ \end{tabular} & \begin{tabular}{c} **Moment by** \\ **Self-Weight** \\ \end{tabular} & \begin{tabular}{c} **Adjusted** \\ **Nominal Flexural** \\ **Strength** \\ \end{tabular} & \
\begin{tabular}{c} **Maximum** \\ **Moment (2)** \\ \end{tabular} &
\begin{tabular}{c} **Ultimate Failure Mode** \\ **(2) to (1) (\%)** \\ \end{tabular} \\ \hline
588-WF-X & 1479.2 & 6.5 & 1472.7 & 1806.5 & \
\begin{tabular}{c}
\begin{tabular}{c} Bending failure + Local \\ flange buckling \\ \end{tabular} & 122.7 \\ \hline
505-TF-X-R1 & 1397.3 & 10.0 & 1387.3 & 1660.3 &
\begin{tabular}{c} Bending failure + Local \\ flange buckling \\ \end{tabular} & 119.7 \\ \hline
505-TF-O-R1 & 1052.0 & 9.7 & 1042.3 & 1256.3 & Web local buckling & 120.5 \\ \hline
505-TF-O-R2 & 977.0 & 9.7 & 967.3 & 1191.0 & Web local buckling & 123.1 \\ \hline
390-TF-O-R1 & 744.5 & 9.2 & 735.3 & 858.3 & Web local buckling & 116.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Test results of the non-composite specimens. \begin{table}
\begin{tabular}{c c} \hline \hline \multicolumn{2}{c}{**Internal Axial Force Component**} & \multicolumn{2}{c}{**Force Equation**} \\ \hline Concrete compression force above PNA (\(C_{conc}\)) & \(C_{conc}=b_{c}\times y_{PNA}\times 0.85F_{ck}\) \\ Compression force at upper flange (\(C_{Af}\)) & \(C_{Af}=b_{f}\times t_{f}\times F_{y}\) \\ Compression force at web above PNA (\(C_{Aw}\)) & \(C_{Aw}=t_{w}\times(y_{PNA}-l_{tc}-t_{f})\times F_{y}\) \\ Tension force at web below PNA (\(T_{Aw}\)) & \(T_{Aw}=t_{w}\times(l_{tc}+t_{f}+h_{A}-y_{PNA})\times F_{y}\) \\ Tension force at upper flange of tube (\(T_{tuf}\)) & \(T_{tuf}=b_{u}\times t_{u}\times F_{y}\) \\ Tension force at web of tube (\(T_{ttw}\)) & \(T_{ttw}=2t_{u}\times(h_{u}-2t_{u})\times F_{y}\) \\ Tension force at lower flange of tube (\(T_{tbf}\)) & \(T_{tbf}=b_{u}\times t_{u}\times F_{y}\) \\ Tension force at main rebars (\(T_{re}\)) & \(T_{re}=n\times A_{re}\times F_{y,re}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Internal force components in case the plastic neutral axis exists below the upper flange. It can be noted from these results that the ultimate failure modes of the non-composite specimens without web openings are mainly characterized by bending failure, while those of the non-composite specimens with web openings are mainly characterized by web local buckling failure. This justifies the theoretical flexural strength estimations of Section 3.1, where the flexural strengths of the non-composite specimens without and with web openings are based on the plastic and yield moments, respectively. The ratios of the experimental and theoretical flexural strengths of the specimens ranges from approximately 117% to 123%, which confirms the effectiveness of the strength equations derived in Section 3.1.