Tracking the progressive collapse of axially-restrained steel beams under fire conditions

This paper investigates structural responses of three axially-restrained steel beams under monotonically rising temperature. Only uniform temperature distribution within a beam is considered. An elastic spring attached at an end of a beam is adopted to simulate axial restraint from the adjoining structure. Three different axial restraint ratios are investigated. Progressive collapse processes of all beams throughout heating are examined, whilst the formulation of plastic hinge at the mid-span is emphasised. Besides, developments of beam internal forces, including axial force and mid-span bending moment, are discussed in detail. Based on the definitions of limiting temperature and collapse temperature adopted in this study, it is found that (1) Increasing axial restraint stiffness will reduce limiting temperature; and (2) beams subjected to greater axial restraint will have longer duration before collapse.