Resonance characteristics of gapped power bus structures with a slit or a gap were studied, using a fast algorithm based on a full cavity-mode resonator model and the segmentation method. Inductance and capacitance models were used to account for a field coupling along the slit and across the gap, respectively. The effectiveness of the segmentation method and the inductance model for the slit has been demonstrated by good agreement between the calculated and measured results, while the capacitance model for the gap is shown to be useful when the coupling between the segments is relatively weak.