###### Abstract
After being damaged in foreshocks and mainshocks, the damage to the buildings would be further superimposed under the cyclic action of the subsequent aftershocks, which causes the buildings to become more vulnerable. Many researchers have investigated the structural responses under earthquake sequences [22; 23; 24]. [PERSON] et al. [25] studied the seismic response of a steel frame using earthquake sequences as inputs and found that the earthquake sequences significantly increase the displacement ductility demands of the structure. [PERSON] [26] stated that the influence of earthquake sequences should be considered an important factor in the seismic risk assessment of buildings. [PERSON] and [PERSON] [27] employed different sets of earthquake sequences as inputs for wood frames and performed probabilistic seismic demand analysis (PSDA) using the IDA approach. The results showed that the average dynamic responses of a structure under earthquake sequences increase by 5% to 20% compared with those under single mainshocks. [PERSON] et al. [28] comparatively analyzed the seismic responses of RC frame structures subjected to actual and synthetic earthquake sequences, which demonstrates that the seismic response of the structure can be severely underestimated if only mainshocks are considered. Using a typical four-story steel frame, [PERSON] et al. [29] analyzed the impact of an earthquake sequence on seismic losses. The results showed that the earthquake sequences increase the structural seismic response and economic loss. In previous studies on the impact of earthquake sequences on structural responses, steel structures and RC structures are the major research subjects, yet the seismic performance of the CFST frame structure with BRBs has rarely been investigated. The application of seismic fragility analysis to the seismic design of buildings can allow an accurate assessment of the seismic performance of building structures, the effective evaluation of the probability of structures reaching different damage limit states under seismic excitation, and a reasonable prediction of the seismic loss of civil engineering structures [30; 31; 32; 33; 34; 35]. [PERSON] et al. [36] carried out seismic fragility analysis of steel frame structures using different combinations of earthquake sequences. [PERSON] et al. [37] studied the seismic fragility of an RC frame structure subjected to multiple earthquakes using finite element (FE) analysis. [PERSON] et al. [38] established a framework for fragility assessments under mainshock-aftershock sequences and conducted fragility analyses on three non-ductile RC frame structures. [PERSON] et al. [39] investigated the collapse fragility of steel frame structuressubjected to mainshock-aftershock sequences. The results from the above studies all indicate that, compared with that under single mainshocks, the seismic fragility of structures under earthquake sequences significantly increases. However, fragility analyses of high-performance structures such as CFST frame structures with BRBs considering both the mainshock-aftershock sequence as an input and the strain rate effect are extremely scarce at present. In this study, the seismic responses and fragilities of a CFST frame structure with BRBs under earthquake sequences including the strain rate effect were performed using numerical simulation. First, the influences of the strain rate effect and BRBs on the seismic response of the CFST frame structure were investigated. Second, the seismic responses of the CFST frame structure with BRBs under single mainshocks and earthquake sequences were comparatively studied considering the strain rate effect. Lastly, based on a probabilistic seismic demand model (PSDM), the seismic fragility curves of CFST frame structures with BRBs under earthquake sequences were generated. The influence of the amplitude ratios of foreshock (and aftershock) to mainshock of an earthquake sequence on the structural fragility was discussed in detail.