Seismic Performance of Enhanced Restrained CFST Frame-Core Tube Structure

In order to fully utilize the load-bearing capacity and seismic resistance potential of the CFST frame-core tube structure and enhance the safety of important engineering structures under strong earthquakes, the enhanced constraint measures including stirrup-confining concrete at column end and “strengthening coupling beam and wall pier ” were used in the CFST frame-core tube structure system. The influence of these measures on displacement response, plastic energy dissipation, stiffness damage, second line of defense and failure mode were discussed. The analysis results showed that:
1)The core tube as the first line of defense for the structure, when the plastic deformation of the structure is small, the measure of “coupling beam and wall pier strengthened” has a greater impact on structural deformation. However, the measure of column end stirrup-confined has a significant impact on the interlayer deformation of the bottom reinforcement area when in the stage of large plastic deformation.
2)The measure of column end stirrup-confined has a significant impact on the seismic performance of the external frame as a second line of defense. It can enhance the loading-bearing capacity of CFST columns and ensure that the columns in external frame do not suffer serious damage during super strong earthquakes. In this case, more torque and shear force are borne by the external frame, coordinating with the core tube to resist seismic force, reducing the damage and plastic deformation of the core tube, effectively exerting the seismic performance of the second line of defense, and ultimately achieving the goal of not collapsing.
3)The measure of column end stirrup-confined has changed the failure mode of “strong core tube and weak frame”, and improved the energy dissipation capacity of concrete-filled steel tube column， significantly improving the toughness of CFST columns and limiting the displacement of the core tube in large plastic deformation, further expanding the energy dissipation range of the wall pier. At the same time, this measure makes the plastic energy dissipation distribution of wall pier in core tube and CFST columns in external frame more reasonable, forming a reasonable double line of defense failure mode, slowing down the degradation of structural stiffness, improving the ductility and seismic toughness of the structure.