How prestressing strands and embedded steel sections jointly govern cracking, flexural resistance and deformation capacity in UHPC beams remains insufficiently quantified. Existing studies mainly address individual strengthening mechanisms, leaving the interaction between prestressing degree and steel-section ratio, and their relative importance among design parameters, insufficiently resolved. Five full-scale beams were tested under monotonic four-point loading, and an OpenSees model was used to compare 24 cases across eight design parameters. A section-equilibrium formulation accounts for UHPC compression and fiber tension, the embedded steel profile, longitudinal reinforcement and prestressing strands. The calculated-to-test moment ratio has a mean of 1.008 and a sample standard deviation of 0.031. Relative to the non-prestressed beam, the L2 cracking load increases by 68.3%. Increasing strand diameter from 12.7 to 17.8 mm increases peak load by 16.72%, while increasing steel yield strength from 235 to 460 MPa increases peak load by 31.38%. The sensitivity matrix distinguishes the dominant parameter for cracking resistance from that for peak-load response, and the ductility comparison identifies how the effect of prestress changes with steel-section ratio. These comparisons quantify the combined strengthening mechanism and connect parameter selection to crack control, flexural capacity and deformation demand.
