The seismic response of existing steel frames is significantly affected by the behaviour of column-base connections. Depending on their design, these connections can exhibit significantly different stiffness, strength, and ductility. While extensive research has been conducted to understand the response of these connections across a wide range of configurations, most studies have focused on uniaxial loading. However, the three-dimensional nature of earthquakes typically subjects these connections to biaxial bending and shear forces. To address this research gap, the ERIES-HITBASE (Earthquake Assessment of Base-Column Connections in Existing Steel Frames) project experimentally investigated the response of exposed column-base connections via bi-directional pseudo-dynamic (PsD) tests. These tests were carried out on a full-scale, three-dimensional steel frame at the Structures Laboratory of the University of Patras, Greece. The steel frame featured two types of column-base connections, i.e., unstiffened and stiffened, representing respectively the base connections of an external moment-resisting frame and an internal gravity frame, respectively. The response of each component of column-base connections was monitored during the PsD-tests to capture their behaviour. This paper presents the preliminary results of numerical simulations conducted for the tested column-base connections. Local and response quantities are investigated, and threshold limits of damage are identified.