## 3 Test Observations and Results
### Load-Displacement Response  
Figure 7 presents the load-displacement response for each specimen, and the corresponding envelope curve is also plotted in each figure using red lines. As for the drift ratio (DR) related to the actual height of the lateral force, 1800 mm was selected due to the distance between the lateral actuator and top face of bottom beam. Therefore, the drift ratio can be defined as the ratio of the displacement and actual height of the lateral force, and it is also plotted in the top axis of the load-displacement response. Moreover, four special states are also identified in the figure: the crack state, max state, ultimate state and final state. The crack state represents the first crack that occurred in the specimens, and the max state indicates that the specimen reached its maximum lateral resistance in the positive or negative direction. As for the ultimate state, there were two definitions commonly used in the literature [6; 7; 8; 9; 10; 27; 28; 29], but it can be considered the state in which the lateral resistance of the specimen decreased to 85% of the maximum lateral resistance, as recommended by the Chinese Code [37]. The final state is the test stop state, when the lateral resistance of the specimen dropped to 60% of the maximum lateral resistance in the positive or negative direction. The measured displacement and load of each specimen were collected, as shown in Table 3. The terms Q and \(\vartriangle\) represent the lateral resistance and corresponding displacement of specimens, respectively.  
In general, all specimens showed a symmetrical hysteretic response and obvious pinching effect. The load-displacement curves for specimens with a different section type showed a different downward trend. The lateral resistance of the T-shape section specimens decreased more abruptly than that of the rectangular section specimens. This can be explained by the fact that a flexure and ductility failure occurred in the rectangular section specimens, while a shear and brittle failure occurred in the T-shape section specimens. Additionally, for specimens BMF and BMFP, the load-displacement curves are similar, but the descending section of the curves is gentler in BMFP than it is in BMF, which is shown by the spacing between the max state and ultimate state in Figure 7a,d. A similar situation also occurred in specimens BMFT and BMFTP. With regard to the measured load and displacement, listed in Table 3, the lateral resistance of the specimen BMFP is 7% higher than that of the specimen BMF, while the lateral resistance of the specimen BMFTP is close to that of the specimen BMFT. Moreover, the specimens with or without prestressing technology reached their maximum lateral resistance at the same drift ratio (except for BMFTP), and this indicated that the prestressing technology had no significant effect on the max state of the specimens. Therefore, the abovementioned results demonstrated that the load-displacement curves were influenced by the section type, and the prestressing technology had beneficial effects on the later stage, after the specimen reached its maximum lateral resistance. In any case, a greater amount of experimental data is needed to support this conclusion.  
Figure 6: Failure modes of the specimens: (**a**) BMF, (**b**) BMFP, (**c**) BMFT, (**d**) BMFTP, (**e**) flange view of BMFT, (**f**) flange view of BMFTP.