## 4 Test Results and Discussion
### Load-Deflection Relationship  
Table 3 lists the cracking load, yield load, and ultimate load of the prestressed beams measured at the mid-span. The cracking, yield, and ultimate loads are the external total loads (P) when the flexural crack starts to occur, the tension steel starts to yield, and the beam starts to fail, respectively. In addition, this table shows the yield of the prestressed beams and the rate of increase in the ultimate load relative to the control beam, as well as the effects of the prestress force introduced to the steel rebar mounted on the lifting hole.  
The load-deflection curves until the point of failure of the tested beams are shown in Figure 5. The load-deflection curves of the prestressed beams, excluding the control beam, exhibit three straight lines, which correspond to the cracking of the concrete, the yield of the tension bar, and the failure.  
Figure 4: Failure modes of tested beams. (**a**) LHS; (**b**) LHT; (**c**) LHU and (**d**) JBM series.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**External Total Load (P)**} & \multicolumn{4}{c}{**Load Increase Rate**} \\ \cline{2-9}
**Beam** & **Cracking Load** & **Yield Load** & **Ultimate Load** & \multicolumn{2}{c}{**Anchorage Type**} & \multicolumn{2}{c}{**Rebar Force**} \\ \cline{4-9}  & & & & **Yield** & **Ultimate** & **Yield** & **Ultimate** \\ \cline{2-9}  & **(kN)** & **(kN)** & **(kN)** & **(\%)** & **(\%)** & **(\%)** & **(\%)** \\ \hline CON & 55 & 133 & 167 & 0 & 0 & - & - \\ LHS & 97 & 188 & 278 & 41 & 66 & - & - \\ LHT & 118 & 251 & 311 & 88 & 86 & - & - \\ LHU & 115 & 225 & 272 & 69 & 63 & - & - \\ JBM & 118 & 280 & 388 & 110 & 132 & 0 & 0 \\ JBM5 & 132 & 299 & 394 & 122 & 136 & 7 & 2 \\ JBM10 & 150 & 318 & 401 & 148 & 140 & 14 & 3 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Test results.  
As shown in Figure 5a, the yield and ultimate loads of the beams, reinforced with a prestressed tendon and fixed with a conventional anchorage, increased by 41% to 88% and 63% to 86%, respectively, as compared with those of the control beam. However, the yield and ultimate loads of the beams with the newly proposed anchorage increased by 110% to 148% and 132% to 140%, respectively. This difference results from the more efficient transmission of the tension force in the prestressing tendon by the proposed anchorage as compared with a conventional anchorage. The conventional anchorages incurred problems such as the stud anchors pull-out, cracking around the anchorage, and local failures between the beam and the anchorage. In contrast, the proposed anchorage did not exhibit such problems, because of its efficient load transmission structure.  
The effects of the changed prestress forces, introduced to the steel rebar, on the load-deflection behavior of the prestressed beams are shown in Figure 5b. Compared with the beams that used a non-prestressed steel rebar (JBM), the beams that used 5 kN and 10 kN prestressed steel rebar (JBM5 and JBM10, respectively) exhibited a moderate increase in their yield load of 7% to 14%, but only a small increase of 2% to 3% in the ultimate load. This can be attributed to the proposed anchorage and concrete beam being more closely adhered to each other, because of the existence of a prestressed steel rebar, which improved the transmission of the prestressing tendon's tensile force on the concrete beam. In other words, the prestressing for the steel rebar was adjudged to have an influence on the tension steel to some degree, and to have delayed the yield of the tension steel. The ultimate load of the beams to which the proposed anchorage was applied was almost identical, regardless of the prestress levels introduced to the steel rebar, as shown in Figure 5b. This is because the failure of the beam was dominated by the yield of the prestressing tendon, rather than by the failure of the anchorage itself.  
Figure 5: Load–deflection relationships of the tested beams. (**a**) Anchorage; (**b**) force in the steel rebar.