This study proposes a novel reduced beam section concrete-filled double steel tube (RBS CFDST) beam-to-column joint and investigates the effect of RBS length and the beam moment of inertia on the plastic hinge formation in such joints. Therefore, a set of nine RBS CFDST connections were fabricated and cast with self-consolidating concrete in the laboratory. Then, parameters including failure pattern, buckling mode, plastic hinge location, joint maximum load-bearing capacity, and column rotation were inspected. The findings reveal that when the RBS length is equal to that of the beam dimension, the entire plastic hinge length is formed within the RBS zone. As such, the plastic hinge occurs away from the column face and brittle failure is avoided, while the joint column rotation is significantly reduced. It was also concluded that the maximum load-bearing capacity is the highest when the RBS length is at its lowest.