Ensuring the composite action in structural members with different components along with optimizing the weight is very challenging and many efforts have been made in this direction in the last decades. This study introduces a new composite beam with partially encased steel sections (PECB) where the shear connectors were mitigated along with superior flexural performance. The innovative connection was done using steel sections with wide flanges and cellular web with circular openings where the section weight was significantly reduced with optimized strength behavior and improved composite action. This study details the flexural performance of PECBs with different cellular configurations. Circular openings were numerically simulated within the steel beam web with different diameters (150, 200, and 250) mm, center-to-center spacing between the two constitutive cells (143, 200, and 250) mm, and the diameter of the longitudinal flexural rebar diameter (12 and 14) mm, with a 500 mm constant distance from each of the beam’s end. The structural behavior was deeply compared with providing an optimized use of the PECB components to maintain their strength and ductility behavior. Results were promising and believed to provide a wide vision of the improved system’s performance.