Abstract: Under a penultimate column removal scenario, the critical sub-frame is in an asymmetrical boundary condition. In that case, the sub-frame suffers a higher risk of collapse. To study the effects of asymmetrical boundary conditions on the progressive collapse behavior of reinforced concrete (RC) frames, three 1/2-scale RC beam-column assemblies subjected to the penultimate column removal scenario were tested with Pushdown loading. The effects of seismic design, non-seismic design and sectional dimension of the column on the load resistance, failure mode and conversion of the load-carrying mechanism were studied. Test results indicate that seismic design allows the sufficient development of catenary action, resulting in higher load resistance. The exterior joint of the assemblies has sufficient shear strength to prevent shear failure regardless considering seismic design or not, which allows the failure of the assemblies to be controlled by the fracture of the beam rebar. In addition, the effects of longitudinal reinforcement diameter, sectional dimension of the column and transverse reinforcement ratio of the joint were studied with the finite element software LS-DYNA. It is found that enlarging the longitudinal reinforcement diameter can increase the load resistance; however, the resulting greater horizontal tension can lead to the large eccentric compression failure of the column. Increasing the sectional dimension of the column has a slight effect on load resistance.