Column base is one of the most important element of steel structures. It is important to investigate the influence of elasto-plastic behavior of column bases on the ultimate earthquake resistance of steel frames. In this paper, a series of inelastic response analysis of multi-story steel frames with exposed type column bases, especially weak anchor bolt type column bases, were carried out. From the analytical results, following conclusions were obtained. 1)The intensity of the damage concentration at the structural element of the 1st story in the frames with exposed type column bases were much less than that of the frames with pin type column bases and the frames with fixed column bases. 2)Ultimate earthquake resistance of the frames with exposed type column bases were similar to that of the frames with pin type column bases. 3)If columns of the frames were ductile, ultimate earthquake resistance of the frames with exposed type column bases were similar to or a little better than that of the frames with fixed column bases. If columns of the frames were not ductile, ultimate earthquake resistance of the frames with exposed type column bases were much better than that of the frames with fixed column bases. 4)Energy absorbing capacity of the exposed type column bases were much less than other structural elements.
