Structural Responses of Axially Restrained Steel Beams with Semirigid Moment Connection in Fire

This paper investigates the structural responses of generally restrained steel beams under fire conditions by the finite-element method. The axial restraint is represented by a linear elastic spring, whereas the rotational restraint is simulated as a semirigid rotational spring. The developments of beam internal forces, crosssectional stresses and strains, together with displacements are examined. Moreover, the effects of some important factors such as load utilization factor, beam slenderness ratio, and axial and flexural restraint ratios, are also studied. Numerical analyses show that the critical temperature is reduced by axial restraint but increased by semirigid rotational restraint. Some stocky beams subjected to low utilization factors buckle at elevated temperature. The later part of the paper focuses on investigating the effect of cross-sectional thermal gradient; the associated thermal bowing is detrimental for a slender beam. This paper also tabulates the finite-element (FE) predictions of the lower and upper bounds of beam critical temperature for design purposes. Besides FE analyses, the simplified methods from EC3 Pt.1.2 and BS5950 Pt.8 for critical temperature are also examined.