Failure mechanism research and load-bearing capacity of externally prestressed composite beams with web openings

The application of external prestressing to composite beams with web openings (CBWOs) significantly extends their elastic working range and optimizes material utilization, manifested through enhanced structural yield moment and load-bearing capacity, increased stiffness, and improved mechanical performance. The present research first defines and formulates the degree of prestress in externally prestressed CBWOs. Finite element models were subsequently developed and calibrated based on experimental data. A total of 15 specimens (12 prestressed and 3 non-prestressed) were designed and simulated, incorporating three variable parameters: span-to-depth ratio (ranging from 7 to 15), type of prestressing tendons (straight vs. draped), and degree of prestress (ranging from 0.22 to 0.37). Results demonstrate that, compared to non-prestressed beams, the yield moment M_y increased by 32-70% and the ultimate capacity M_u increased by 48-60%. The tendon profile (straight or draped) exhibited a negligible impact on structural capacity. A model for the ultimate prestress increment Δσ_{p, ui}, dependent on the span-to-depth ratio λ, was established and achieved excellent accuracy in predicting M_u. These findings provide valuable insights for optimizing prestressed composite beam systems in structural engineering practice.