1. Elevated Temperature Effects on Local Buckling of Wide Flange Columns
- Author
-
Baidar, Nikki
- Subjects
- Civil Engineering, local buckling, elevated temperature, fire condition, steel column, finite element modeling, wide flange column
- Abstract
Wide flange steel columns under compression that are designed for ambient conditions may fail due to local buckling when subjected to fire conditions. At elevated temperatures, the sections may behave as slender elements due to strength and stiffness reductions in the mechanical properties of the steel. There is currently no provision in the AISC Specification (2016) for determining the local buckling capacity of columns under fire. This work aims to build on previous studies to better understand the local buckling capacity of columns subjected to uniaxial compression at elevated temperatures. A finite element modeling program, ABAQUS, was used to develop numerical models of wide flange steel columns under fire conditions. A parametric study of steel stub columns subjected to different temperatures (ambient, 400°C, and 600°C) and various section slenderness ratios was conducted. ASTM A992 steel (Gr. 50) steel columns were analyzed to determine the effect of temperature and section slenderness on the local buckling of columns at elevated temperatures. Three different wide flange steel cross-sections, W14×120, W12×96, and W10×88, were studied and their flange and web thicknesses were varied. Some sections that failed due to global buckling at ambient temperature failed due to local buckling at elevated temperatures. When the applied temperature in the column increases, the load capacity of the steel column decreases. Additionally, the column load capacity at elevated temperatures decreases as the slenderness ratio of the cross-section (flange and web) increases. The flange slenderness has a greater influence on column capacity than the web slenderness. The columns with high interactive slenderness ratio were most affected at 600°C.The load capacity for each column was estimated using the current AISC 360 (2016) equation for local buckling at ambient temperature; however, the material properties (yield strength and modulus of elasticity) were modified to correspond to elevated temperature properties. These calculated values were compared to the failure load determined from the modeling for each of the steel columns. The present AISC equations were found to be inadequate for determining the local buckling capacity of a column with slender elements at elevated temperatures. An interactive slenderness term was defined as (λf/λrf) (λw/λrw), where λf is the flange slenderness of the column, λw is the web slenderness of the column, λrf is the limiting slenderness ratio of flange, and λrw is the limiting slenderness ratio of the web. Thus, the ratio of flange slenderness to limiting flange ratio was multiplied by the ratio of web slenderness to limiting web ratio to develop a slenderness term that incorporates both web and flange slenderness together. As the interactive slenderness of the column increased, the AISC 360 (2016) provisions over-estimated the column capacity at 400°C and 600°C.An equation must be developed to better estimate the local buckling capacity at elevated temperature. Results of this study will serve as the basis of efforts to formulate an independent design equation for local buckling of wide flange columns under fire load. This design equation would be incorporated into the simple method of analysis within Appendix 4 of the AISC Specification (2016).
- Published
- 2022