## 4 Load Test Results and Discussion  
Figure 14 presents the final failure patterns of all of the specimens after the mechanical tests. The following can be observed:  
(1) The failure modes of the unstrengthened specimens S60 and S120 were similar to that of untreated specimen S0. All three specimens primarily experienced concrete crushing in the compression region of the joint. However, flexural cracks in the tensile zones of the former two specimens were fewer than in the latter. (2) The failure patterns of strengthened specimens S60C and S120C were similar. Flexural cracks were observed on the back and front of the FAC, however they did not oblique propagate deep into the segment concrete. In addition, some cracks in the direction of the anchor bolt's root were found on the tension side of the specimens, and these cracks were resulted from the shear force transmitted from the bolts to the FAC. After the occurrence of the shear cracks, the restraint effect of surrounding FAC on the anchor bolts reduced, resulting in a certain bending deformation of the bolts. However, fracture of the anchor bolts was not observed during the loading tests. The epoxy adhesive between the strengthening members and the FAC experienced some local failure, and local debonding between the FAC and the segment concrete was observed. Figure 13: Measured temperature-time curves of joint bolts. (**a**) Heating duration = 60 min; (**b**) heating duration = 120 min. The measured ultimate loads \(F_{\text{v, max}}\) (maximum load in the vertical direction) of all of the specimens are listed in Table 4. The bearing capacities of Specimens S60C and S120C were large and beyond the capacity of the vertical actuator, so for those two specimens it is the maximum applied load (1455 kN) instead of the ultimate load that is listed in Table 4. Also included in Table 4 are the initial stiffness (i.e., the secant stiffness at 30% \(F_{\text{v, max}}\)) of all the specimens. As can be seen, the ultimate loads of the unstrengthened specimens S60 and S120 were about 24% smaller than that of the untreated specimen S0, the ultimate loads of strengthened specimen S60C and S120C were at least 55% larger than those of the  
Figure 14: Concrete crushing and cracks. (**a**) Specim S0; (**b**) specimen S60; (**c**) specimen S120; (**d**) specimen S60C; (**e**) specimen S120. unstrengthened specimens and at least 17% larger than that of the untreated specimen S0. In addition, the initial stiffness of the strengthened specimen was at least 550% larger than that of the untreated specimen and at least 360% higher than that of the untrengthened specimen. It seems, therefore, that a fire-damaged segment joint can maintain considerable loading capacity and initial stiffness even surpassing those of an untreated segment joint if it is strengthened with the proposed CFST. Table 4 also shows that exposure to fire for 60 or 120 min had no effect on the ultimate load of the untrengthened specimens. The reason is probably that most parts of the joint bolts in Specimens S60 and S120 were not exposed to the fire directly. The temperatures of the joint bolts' mid-points were below 220 \({}^{\circ}\)C throughout the fire testing. Consequently, the residual mechanical properties of the joint bolts were very similar after cooling [26]. Moreover, regardless of whether the fire lasted 60 or 120 min, the compression regions of the segments experienced only room temperature because they were so far from the heated surface. Thus, the duration of exposure to fire had little effect on the specimens' bearing capacity. The relationship between the applied load and mid-span deflection for all of the specimens is presented in Figure 15. The following can be observed:  
(1) The flexural stiffnesses of the untrengthened specimens S60 and S120 were generally higher than that of the untreated specimen S0.