The concrete infilled rectangular steel tube（CIRST） column is a kind of typical member used in light-weight steel frame structures.The explosion happening in the building due to the gas leaking may cause severe damage to the CIRST columns.However

less attention was paid to the enormous damage to the column under the blast loading.A typical CIRST column is numerically analyzed in the paper to investigate the dynamic responses and failure modes under the blast loading by using finite element software ANSYS/LS-DYNA.A solid model is made for the numerical analysis of the column.The MAT-PLASTIC-KINEMATIC model and the JHC model are used for the steel tube and the infilled concrete

respectively

to consider the strain rate effect.The blast loads are hypothetically applied to the surface of the column.The dynamic responses of the CIRST column are numerically analyzed and the attention is focused on the failure modes under different scaled distances of explosions.The numerical simulation shows that the failure mechanism of the CFRST column may be described as that the rectangular steel tube has a certain confined function for the infilled concrete to increase the strength of the concrete in complex stress state

and the ductility and toughness performance is also improved at the same time

resulting in delay of the early local buckling because of the existence of the concrete.As increasing of the scaled distances of the explosion

the horizontal displacement of the column at the middle span is also decreased.The results also show that the CIRST column has the excellent ductility and blast resistance.The failure mechanism and the numerical analysis method developed in the paper may provide a reference for the design of the structure under blast loading.