The tendon stress in bonded prestressed concrete (BPC) beams is section-dependent while it is member-dependent in unbonded prestressed concrete (UPC) beams, leading to marked difference between these two structural systems. However, little work has addressed the bond effect of steel tendons. This research presents comparative investigations of BPC and UPC beams with various prestress levels. A numerical model is experimentally validated. Numerical assessments are conducted for simply supported and continuous scenarios, focusing on the effects of bond condition and prestress level. The results show that BPC beams exhibit better crack pattern (i.e., smaller crack width with larger crack zone) than UPC beams. The difference in ultimate loads or deflections between BPC and UPC beams depends heavily on the prestress level (the values of UPC beams are around 64% and 94% of those of BPC beams at prestress levels of 25% and 75%, respectively). Unbonded tendons produce greater moment redistribution in continuous scenarios than bonded tendons. It is also shown that the ACI code cannot well describe the bond impact of steel tendons on moment redistribution in continuous scenarios. A modified ACI equation is proposed, which can predict accurately the moment redistribution in both BPC and UPC beams.

The present investigation aims to identify the flexural performance of two-span concrete beams reinforced with hybrid carbon fiber reinforced polymer (CFRP) and steel bars. By applying a finite element analysis, a comprehensive numerical assessment is performed. The investigated variables are A_f/A_r (A_f = area of CFRP bars; A_r = total area of CFRP/steel bars), load pattern (symmetrical and unsymmetrical loading) and load type (center-point, third-point and uniform loading). The results show that beams with A_f/A_r of 0.25 show 16.0% and 11.3% higher ultimate load at symmetrical and unsymmetrical loading, respectively, than beams with A_f/A_r of 0.0 (i.e., beams with steel bars), but the change in ultimate load is not apparent when varying A_f/A_r between 0.25 and 1.0. Unsymmetrical loading causes 6.0–15.0% greater deflection capacities than the symmetrical one. When A_f/A_r increases from 0.0 to 1.0, moment redistribution at symmetrical loading is decreased significantly by 62%, while the redistribution variation is marginal at unsymmetrical loading. In addition, the applicability of two equations based on the ultimate strain in tensile bars for predicting moment redistribution is evaluated. It is generally shown that these equations can account for the influence of A_f/A_r and load type.

This study investigates hybrid fiber-reinforced polymer (FRP)–steel-reinforced concrete (RC) beams by using three-dimensional finite element models. The research systematically analyzes the influence of key parameters, including FRP type, FRP bar ratio (ρ_f), the ratio of FRP to total reinforcement (ρ_f/ρ_t), and concrete strength. The load–deflection response of the hybrid RC beams is analyzed in detail. The results show that the investigated parameters have a relatively limited influence on the cracking moment, but significantly affect both the yield and ultimate moments. When ρ_f/ρ_t increases from 0 to 0.75, the yield moment decreases by up to 44.34%. When ρ_f increases from 0.55% to 0.88%, the yield moment increases by 50.63%. Meanwhile, increasing the concrete strength significantly enhances the ultimate moment, with a maximum increase of 38.46%. In addition, an energy ductility index is adopted to quantitatively evaluate the structural ductility. The results indicate that the energy ductility index is consistently lower than the conventional ductility index. Finally, to improve the accuracy of theoretical predictions, a semi-empirical simplified formula is proposed for estimating the FRP bar stress at the ultimate state of hybrid beams. The verification results show that the proposed prediction method agrees well with the experimental data, demonstrating that the simplified formula has good applicability and reliability within the parameter range investigated in this study.