## 2 Experimental Program
### Specim Grouping and Design
#### 2.1.1 Specimen Grouping and Comparison Setting  
Four influencing factors, namely the self-stress, initial damage, length-diameter ratio, and reinforcement ratio of the LCSS, were set as the control variables of the specimens. The following were conducted for the other factors: (a) The thickness, strength, and reinforcement ratio of the filled concrete were not considered key control variables for the seismic performance of specimens because numerous studies [40; 44; 45; 51; 52; 53; 54; 55] have analyzed the impact of these three common variables on the seismic performance of columns and reached similar conclusions; that is, the high reinforcement ratio of the filled concrete can significantly improve the bearing capacity and ductility of columns under low cyclic horizontal loads [44]. (b) Compared with the improved connection performance of the segment sleeve, the influence of the LCSS thickness and concrete strength on the seismic performance of piers was relatively small. The LCSS thickness remained constant due to the limitations of the prefabricated mold used for the segments. Hence, investigating only the effect of weakening the segment sleeve reinforcement ratio on the seismic performance is sufficient. (c) Considering the slight variation in the axial compression ratio during the loading process of the piers [2], the same axial compression ratio was adopted for all test specimens. Moreover, several variables, including the segment thickness, reinforcement ratio, filled concrete strength, and axial compression ratio of the pier column, were considered in subsequent numerical simulations for the extended parameter analysis.  
As shown in Table 1, the nine specimens were divided into three groups (G0, G1, and G2) based on the experimental objectives. The test control group (G0) included three unreinforced specimens: pier column specimens without SSAWC or LCSS. G1 included a specimen strengthened with AWC and LCSS. G2 included five specimens strengthened using the IPCSAM; G2 samples were used to explore the effects of different control variables on the seismic performance of the strengthened piers. Five comparison groups were set up as follows: (a) Comparisons between UP-1 and RP-1, UP-2 and RP-4, and UP-3 and RP-5 to investigate the seismic strengthening effect of the piers strengthened using the IPCSAM under the same length-diameter ratio; (b) Comparison between RP-0 and RP-1 to investigate the effect of the self-stress produced using SSAWC on the seismic performance of strengthened piers; (c) Comparison between RP-1 and RP-2 to investigate the effect of the reinforcement ratio of LCSS on the seismic performance of strengthened piers; (d) Comparison between RP-1 and RP-3 to investigate the effect of the initial damage on the seismic performance of strengthened piers and verify the repair effect of the IPCSAM technology on the initial pier damage; (e) Comparison between RP-1, RP-4, and RP-5 to investigate the effect of the length-diameter ratio of the LCSS on the seismic performance of strengthened piers. According to relevant research [25], the errors for three test specimens with the same parameters are generally within 10%. Hence, to accelerate the test process, the preparation of only one specimen with the same parameters as in this experiment was sufficient. The values of the control variables were determined using Reference [2] and Code [55; 56].