# Long-Term Behavior of RC Beams Strengthened with Hybrid Composite Beam
## 3 Experimental Results and Discussions  
### Long-Term Deflection  
The measured instantaneous and long-term deflections for the unstrengthened and HCB-strengthened RC beams under the two different sustained loadings are summarized in Table 2. It was observed that the instantaneous deflections of HCB-strengthened RC beams are approximately 15% and 38% lower than those of unstrengthened RC beams at 33% and 50% sustained loadings, respectively. Also, it was found that the long-term deflections of HCB-strengthened RC beams after 1 year were approximately 245% and 176% higher than those of the instantaneous deflection at 33% and 50% sustained loadings, while the long-term deflections of unstrengthened RC beams were approximately 278% and 152% higher than those of the instantaneous deflection at 33% and 50% sustained loadings, respectively. For more details, the time-dependent deflections of the HCB-strengthened RC beams at 1, 3, 6 and 12 months were approximately 24%, 14%, 22% and 25% lower than those of the unstrengthened RC beams under 33% loading level, respectively. The time-dependent deflections of the HCB-strengthened RC beams at 1, 3, 6 and 12 months were approximately 30%, 29%, 29% and 28% lower than those of the unstrengthened RC beams under 50% loading level, respectively.  
Therefore, it can be concluded that HCB strengthening of the RC beams not only reduced the instantaneous deflection but it was also effective in controlling the time-dependent deflection for the entire time. In this investigation, as expected, we found that both the instantaneous and long-term deflections of both unstrengthened and HCB-strengthened RC beams at a higher loading level were increased, and the influence of HCB strengthening on the long-term deflection of RC beams is roughly proportional to the level of applied sustained loading. Figure 6 presents the graphical curves of additional deflections at the mid-span, along with loading time. The additional deflections in this study were obtained by subtracting the instantaneous deflection from the total deflection at given specific times. At 33% loading level, the additional deflections of HCB-strengthened RC beams were smaller than those of unstrengthened RC beams. However, the additional deflections of HCB-strengthened beams at 50% loading level showed similar values to the unstrengthened RC beams. At a higher loading level, a further investigation is needed due to such an unexpected result from the findings of this study.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Time (days)** & **NHCB 33 (mm)** & **HCB 33 (mm)** & **NHCB 50 (mm)** & **HCB 50 (mm)** \\ \hline
0 & 5.14 & 4.35 & 16.15 & 10.05 \\ \hline
30 & 9.25 & 7.06 & 19.26 & 13.48 \\ \hline
90 & 10.69 & 9.19 & 21.08 & 15.07 \\ \hline
180 & 12.73 & 9.93 & 22.29 & 15.91 \\ \hline
360 & 14.32 & 10.77 & 24.54 & 17.72 \\ \hline \hline \Figure 7 shows the relationship between instantaneous deflection and the deflection of HCB-strengthened and unstrengthened RC beams. As seen in Figure 7, the ratios at a specific time of higher sustained loading level for unstrengthened and HCB-strengthened beams showed somewhat higher values than those of the relatively lower sustained loading level. This means that the strengthened and unstrengthened RC beams subjected to the higher sustained loading load level seemed to have no advantage for long-term deflection compared to lower sustained loading levels. This observation from this study was not clearly seen in other investigations.