Abstract: A multi-layer steel frame model without floors was established by ABAQUS. Using sequential heat-solid coupling method, taking into account the location of fire, the power change of fire, non-uniform temperature field and the failure of beams under fire,the initial destruction mechanism and collapse mechanism of the steel frame structure were studied under the influence of 2 factors of the fire form of beam and columns and the location of failure column. The results showed that the continuous collapse of the steel frame structure begins with the failure of the fire column, and the deflection of the beam connected to it increases and the beam produces a pull force due to the loss of support. Then the load distribution columns produce a side shift and the displacement of the structure develop under fire. The destruction spreads to the surrounding and eventually leads to the progressive collapse of the structure. When the bottom failure columns are on the edge, the collapse will be overturn type. When the bottom failure columns are mainly on the structural symmetry axis, the collapse will be sinking type. This type of collapse takes place suddenly.

Key words: steel frame structure, actual fire temperature field, thermal-solid coupling method, progressive collapse