Integrated Serviceability and Embodied Carbon Optimization of Bonded Post Tensioned Concrete Beams Under Time Dependent Prestress Loss

A transparent analytical framework was developed to couple staged prestress loss, transfer and service behavior, flexural and shear resistance, material inventory, multiobjective selection, and exploratory reliability for bonded post-tensioned rectangular beams. Within the assumptions and discrete domain of this study, the following conclusions are drawn. ·        Full enumeration evaluated 48,600 designs and retained 13,859, demonstrating that a large portion of plausible geometric combinations is rejected once transfer, service, cracking, deflection, effective-force, and ultimate checks are imposed together. ·        Prestress loss should be maintained as visible components. Friction and anchorage, elastic shortening, shrinkage, creep, and relaxation have different causes, time scales, and project data; one total percentage cannot be calibrated or audited with the same clarity. ·        The selected 15 m compromise is 15 m  300 x 1450 mm  fck 60 MPa  16 strands  e/h 0.25  C40. It has predicted final loss 16.3 percent, carbon indicator 2693 kg CO2e, and governing utilization 0.525. ·        The compromise reduces the controlled cradle-to-gate indicator by 24.9 percent relative to the defined conventional baseline. This saving is conditional on scenario carbon factors and equal analytical function, not a universal product claim. ·        The 15 m minimum-carbon point reaches 1708 kg CO2e and utilization 0.895. Its illustrative Monte Carlo service-tension reliability index is only 0.47, showing that deterministic feasibility near a boundary can have limited robustness. ·        The selected compromise produced no sampled failures in 100,000 trials under the illustrative model. The reported beta 4.42 is a finite-sample bound and should not be interpreted as code-calibrated reliability. ·        Depth, eccentricity, and force are complementary variables. Greater tendon force alone can worsen transfer stresses and steel-related carbon; greater eccentricity can increase transfer tension; and greater depth improves stress and deflection efficiently but raises concrete quantity and may conflict with architecture. ·        Low-carbon concrete must be assessed with the same mixture-specific early strength, modulus, shrinkage, creep, durability, curing, and environmental data used in the structural model. Strength and a generic carbon reduction factor are insufficient for final selection. ·        The framework is suitable for preliminary research comparison and teaching. Project use requires clause-specific code checks, verified material and tendon-system data, anchorage-zone and durability design, construction-stage analysis, and experimental or field validation where response is sensitive. The central design implication is that sustainability and serviceability should be optimized in the same calculation loop. When they are separated, a low-carbon material choice may be credited without its deformation behavior, or a structurally conservative tendon force may be selected without accounting for steel inventory and transfer risk. An integrated, auditable Pareto approach keeps those consequences visible and gives the engineer a defensible basis for choosing reserve.

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