Comprehensive Analytical Framework for Prestressed Steel–Concrete Composite Beams: Verification and Parametric Evaluation

This study develops a comprehensive analytical framework to predict the flexural behavior of externally prestressed steel–concrete composite I-girders (EPCIBs) subjected to positive bending. The analytical model is formulated using strain compatibility and internal force equilibrium and accounts for elastic–plastic behavior of concrete, structural steel, and external tendons. Validation against three independent experimental programs demonstrated strong accuracy, with differences in ultimate moment within 5–8%, mid-span deflection within 6–10%, and tendon stress increments within less than 6% compared with measured results. Additional validation against nonlinear ABAQUS finite element (FE) models confirmed similar accuracy, with ultimate moment discrepancies generally below 8%. A comprehensive parametric study quantified the sensitivity of EPCIB behavior to span length, shear-span ratio, prestressing level, concrete slab properties, and steel-section geometry. Increasing the initial prestressing force from 160 kN to 300 kN increased the ultimate moment capacity by 10–15% and reduced service-level deflection by 18%. Increasing slab thickness from 60 mm to 120 mm enhanced capacity from 230 kN·m to 380 kN·m (a 65% increase), while increasing slab width from 600 mm to 1200 mm produced a moderate 10–12% capacity gain. Enhancing steel section dimensions showed the highest influence: increasing bottom-flange width from 200 mm to 300 mm increased strength by 30–35%, increasing bottom-flange thickness from 8 mm to 14 mm improved capacity by 55–60%, and increasing web depth from 200 mm to 400 mm more than doubled the flexural capacity (up to 150% increase, reaching 780–800 kN·m). Web-thickness variations (4–8 mm) produced smaller gains of 25–30%.