Analytical Fire Resistance of Axially Restrained Steel Columns

Using the standard fire resistance test to predict the fire resistance of a steel column is expensive and time consuming as well. On the other hand, numerical approximation using the finite element method assumes the availability of a nonlinear elastoplastic analysis software. This approach is not necessarily accurate as it does not explicitly take creep into account. As an alternative, theoretical analysis that can be performed manually is a convenient tool for engineers to quickly assess the column fire resistance. This study extends the traditional Rankine formula to the critical temperature prediction of an axially restrained steel column. A linear spring attached to the column top end accounts for the axial restraint of upper-story structure on the isolated heated column. The proposed Rankine approach incorporates both the axial restraint and creep strain. Comparison of test and numerical results using self-developed viscoelastoplastic analysis shows that the proposed Rankine formula yields very good column critical temperatures. Most importantly, it shows that axial restraint can significantly reduce the fire resistance of a column based on the adopted failure criterion.