Predicting the Onset of Instability in Steel Columns Subjected to Earthquakes Followed by Nonuniform Longitudinal Temperature Profiles

Abstract

Historical earthquake events have demonstrated the destructive potential of postearthquake fire and the vulnerability of structural systems to such multiple events. Current well-established seismic design provisions, however, require structural engineers to design structural systems to resist ground motions with no concerns regarding subsequent earthquake-induced hazards. This is primarily because efforts pertaining to developing design provisions addressing the response of building systems under both hazards are still lacking. The ramifications of ignoring the effect of both hazards in design codes could be substantial because of the increased potential for column failure as a result of residual interstory drifts caused by the preceding earthquake event, followed by the fire loads. To that end, the present study aimed to propose design equations to determine the nominal strength of W-shape steel columns subjected to fire following earthquake. The fire load effect was simulated through the application of nonuniform temperature profiles in the columns. The proposed equations account for the residual stress distribution in W-shape steel sections, initial out of straightness and out of plumbness, temperature-dependent material properties, nonuniform longitudinal temperature profiles, and residual interstory drift at the conclusion of an earthquake. The formulations can also accommodate various boundary conditions at column ends. The results clearly highlight the observable reduction in column strength under fire as a result of the preimposed lateral drifts. The results and the proposed equations can be used to quantify the potential for instability in steel columns when subjected to fire following an earthquake.