Pre-fabricated load-bearing beam (10) which extends between two opposing ends (10a, 10b) along a longitudinal axis (X) and comprises a bottom plate (12) and a reinforcement (11), having at least one reticular lattice (13, 14), one or more reinforcement bars (16) parallel to said longitudinal axis (X), and rest members (18) in correspondence with said opposing ends (10a, 10b).