*3.3. Failure Process and Modes*


the joint of the LCSS and the interface between the filled concrete and the column. It should be noted that all bolts remained unbroken.

(3) Self-stressed strengthened specimens: The failure process and modes of the three strengthened specimens were similar, as shown in Figure 9. When the load was close to 2000 kN, the first crack appeared in specimen S1-S, then the crack developed with the increases in load, making a cracking sound in the process. When the load reached 2600 kN, several segments broke and the bearing capacity of specimen S1-S reached the peak and stabilized for a period of time. Then, the bearing capacity dropped and the cracks appeared at the interface between the filled concrete and the column when the bearing capacity dropped to 2250 kN. Finally, as the load decreased continuously, multiple cracks penetrated and the specimen failed. When specimen S1-SS was loaded to 1730 kN, cracks of concrete appeared in the segment concrete. When the load was close to 1850 kN, interface cracks appeared and developed toward the segments. When the load was close to 2150 kN, the segments at the top of the specimen almost failed and the bearing capacity reached the peak, then bearing capacity continued to decrease with long penetrating cracks appearing in many places until the specimen failed. When specimen S2-S was loaded to 1500 kN, concrete cracks appeared in the segment. When it was loaded to 1920 kN, fractures occurred in the segment due to the penetration of the cracks and the bearing capacity reaching the peak. Then, the bearing capacity decreased with the appearance of long penetrating cracks and the specimen finally failed. In this group, the cracks were concentrated on the concrete cover of the longitudinal bolt and the segment joints and none of the bolts were broken. Through testing and calculation, the self-stress values of the reinforced specimens could be obtained, as shown in Table 6.

**Figure 7.** Failure of the unreinforced specimens. (**a**) P1 axial compression failure; (**b**) P2 axial compression failure.

**Figure 8.** Failure of ordinary strengthened specimen. (**a**) Interface cracks; (**b**) LCSS fractures.

**Figure 9.** Failure diagram of self-stressed strengthened specimens. (**a**) Cracks on LCSS of specimen S1-S; (**b**) Fractures on LCSS of specimen S1-S; (**c**) Fractures on LCSS of specimen S1-SS; (**d**) Fractures on LCSS of specimen S2-S.


**Table 6.** Results of test.
