This paper presents a study on the seismic response of multi-tiered braced steel frames. The seismic demand and stability of the columns in a 4-tiered special X-braced frame structure located in a high seismic area and designed according to current AISC seismic provisions is evaluated. The drift demand in the individual bracing tiers and the combined column axial force and in-plane flexural demand are evaluated through nonlinear time history analysis. Detailed finite element analysis of one column under demands extracted from time history analysis is carried out to investigate the buckling response of the column. The results show that high in-plane bending demand is induced in the columns. Flexural yielding caused by non-uniform tier drift demand may detrimentally affect the torsional-flexural stability of the columns.
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