This paper experimentally investigates the seismic behavior of three large-scale hollow-core fiber-reinforced polymer-concrete-steel (HC-FCS) columns. An HC-FCS column consisted of a concrete shell sandwiched between an outer glass fiber-reinforced polymer (GFRP) tube and an inner steel tube. Both tubes provided continuous confinement for the concrete shell along with the height of the column. The columns had two different steel tube diameter-to-thickness (Ds/ts) ratios of 85, and 254. Each steel tube was embedded into the footing, with an embedded length of 1.25-1.6 times its diameter, while the GFRP tube was not embedded into the footing. Two columns were tested as as-built specimens. Then, one of these columns was repaired and re-tested. This study revealed that HC-FCS columns having a high Ds/ts ratio of 254 and short embedded length (1.25 Ds) do not dissipate high levels of energy and display nonlinear elastic performance due to severe steel tube buckling and slippage. However, the column with a Ds/ts ratio of 85 combined with substantial embedment length (1.6 Ds) results in a nonlinear inelastic behavior, high-energy dissipation, and ductile behavior. A retrofitting technique for a high Ds/ts ratio HC-FCS column precluding buckling of the inner steel tube was proposed and examined. The retrofitting method was characterized by the use of an anchorage system with steel tube concrete filling at the joint interface region. The retrofitted column achieved the ductile behavior and performed well under seismic loading with flexural strength increased by 22%. However, the lateral displacement capacity decreased by 26% compared to the original column due to the residual deformations and stresses exhibited during the previous test.