A comprehensive experimental apparatus for the progressive collapse testing of steel frames has been developed. The apparatus is suited for the testing of planar steel frames to study the load transfer process and the progressive collapse resistance of steel structures under a column removal scenario. In order to simulate a sudden removal of a middle column at the ground storey of the frames, a removable column unit has been designed to allow for an instantaneous knock-out by a pendulum hammer during the test. To avoid the out-of-plane instability of the planar steel frames, an out-of-plane restraining system has been designed and integrated into the test apparatus. Weights simulating the desired gravity loads were attached to the test frame through holding baskets, which were designed to minimize unwanted shaking and ensure that the suspended baskets moved together with the deformed steel frames during the tests. Experimental results showed that the column removal mechanism in the test apparatus was effective. Using this apparatus, the dynamic behaviour of three planer steel frames under a column removal scenario was investigated. Based on the measured deformations and strains, the dynamic response, collapse modes, load transfer path of the steel frames after the removal of the middle bottom column are studied.