Behaviour of Wide Flange Steel Columns under Elevated Temperature

Wide flange steel columns are made of structural steel and it consists the deepest I-section. Wide flange shapes are widely used for beams, columns and other architectural members, as well as in pile foundations, bridges and other civil engineering works. Cities in redevelopment, high-rise buildings under construction, freeways undergoing modernization these and many other projects call for wide flange shapes because of their outstanding properties such as high strength, uniformity, light weight and its ease of use than reinforced concrete. Although it has many advantages, it also has many disadvantages that steel columns sometimes cannot provide the necessary strength due to buckling, whereas RC columns are generally free from buckling problems. Also its strength reduces tremendously at high temperature due to common fire. Review of literature says that the failure behaviour of these members when subjected to a compressive force and elevated temperature is still not fully understood as it is confirmed by the numerous different design approaches for these members in various national specifications for steel structures. So the study reveals the fact that how structural systems perform under realistic uncontrolled fire situations. This study concerns hot-rolled ISWB I-section members and their failure behaviour under axially applied compression load under elevated temperature. Wide flange I-sections selected for the analysis covering selected sections from ISWB 150 & ISWB 175. Dimensions and specifications of rolled steel beam sections taken are as given in the steel table. In most of the situations, height of the column is about 3m with both end hinged support condition, both end fixed support condition and one end fixed and other end hinged support condition. During fire situation, the temperature rises from 27C (room temperature) to an approximate temperature of about 700C. So a temperature range of about 27 - 700C is selected for the study. This consists a parametric study employing nonlinear finite element analysis to model the response of wide flange steel columns at elevated temperature. Different axial loads and different cross sections are included in the parametric study. The FEM modelling using ANSYS (Mechanical APDL 14.0) was used to conduct parametric studies to evaluate the effects of different heating configurations on steel column. The failure behaviour at elevated temperature depends on the column cross sectionl area, axial load and temperature. The column sections were uniformly heated until they exhibited either elastic or inelastic buckling failure. As the members are heated the Youngs modulus and yield strength are reduced, which results in slender elements at elevated temperature. Typical cross sectional area is addressed through limiting the element width to thickness ratio, so only member buckling occurs. An indication about the column strength and failure behaviour at elevated temperature is the outcome of this thesis work. This includes the comparative study of buckling modes and failure pattern. Ultimate column strength in various cross sectional areas are different. For an average loading and temperature condition most appropriate cross section to be determined. Failure behavior at elevated temperature is still understood under loading conditions, thus the finite element modeling gives its behavior that it may buckle along its weak axis.