The behaviour of hot-rolled steel I-section beams was studied experimentally and numerically in uniform temperatures in the past, but only limited experimental data are available for localized fire tests. The present paper reports ten experimental tests for short to medium-range laterally unrestrained I-beams of Class 1 section with a non-dimensional slenderness ratio in the range of 0.74 to 1.1. The localized fire behaviour of unrestrained I-beams is experimentally studied with a high thermal zone having a temperature range of 595 to 1200 °C. Three-point loading is provided considering simply-supported boundary conditions with pre-load and peak load (ultimate load) in the range of 0.26 to 0.76 of the design load capacity of a beam member at ambient temperature. The two types of fire scenarios are considered (a) fire concentration at the middle of the span and (b) fire concentration near the support of the beam under steady and transient experimental conditions. The geometrical imperfection is measured using an industrial blue-light optical scanner. A numerical validation study was also conducted using the robust FE modelling software ABAQUS. The experimental study concluded that failure mode can depend on fire location, load ratios, and span length. In the case of localized fire at the middle of the span, lateral torsional buckling happened, and when the fire was near support, local buckling happened at higher load ratios. However, local buckling happened in the beam for lower to mid-load ratios. It is observed that the steady and transient fire tests provided a negligible effect on the response of the beam member. The experimental and numerical results are in good agreement, with a mean percentage variation of 1.5 %, with a maximum value of up to 4.67 %. The study provides quite a simple experimental setup that can easily be replicated for different types of members that enhance the fire safety study of structure. Further, a parametric study is conducted under simply-supported and varying end restraints condition at supports.