Coupled Environmental–Mechanical Deterioration Modeling of Prestressed Concrete Beams Under Freeze–Thaw and Corrosion Actions

A three-dimensional time-dependent finite element model is developed to investigate the short-term and long-term mechanical behavior of prestressed concrete beams subjected to combined freeze–thaw deterioration, tendon corrosion, and sustained loading. The proposed framework integrates smeared cracking and tension stiffening of concrete with concrete creep and shrinkage, prestressing tendon relaxation, freeze–thaw-induced degradation of concrete mechanical properties, and corrosion-induced deterioration of reinforcing steel and prestressing tendons. These mechanisms are incorporated into a unified incremental time-stepping analysis to capture the progressive deformation and prestress loss of the beams. The model is validated against experimental results for corroded prestressed concrete beams, freeze–thaw-damaged concrete beams, and long-term sustained-loading tests. Parametric analyses are subsequently performed to investigate the effects of concrete strength, freeze–thaw cycles, tendon corrosion rate, and prestress level. The results show that increasing the concrete strength from C35 to C50 reduces the 1000-day long-term deflection from 24.1 mm to 18.0 mm. Freeze–thaw deterioration has the most pronounced effect: the 1000-day deflection increases from 13.0 mm at 0 cycles to 42.9 mm at 150 cycles. In contrast, increasing the tendon corrosion rate from 0% to 12% increases the 1000-day deflection only from 21.6 mm to 21.8 mm, although the corresponding long-term prestress loss increases from 188.2 MPa to 198.0 MPa. Increasing the prestress level from 0.45 fptk to 0.75 fptk reduces the long-term additional deflection from 11.4 mm to 8.8 mm. The results demonstrate that freeze–thaw deterioration and concrete time-dependent effects dominate the long-term deformation response, whereas the influence of tendon corrosion on global deflection is comparatively limited within the investigated corrosion range. The proposed framework provides a numerical approach for assessing the time-dependent mechanical response of prestressed concrete beams under combined environmental and mechanical deterioration.