Analysis of box girder based on cross-sectional variations

Box girders are widely utilized in prestressed concrete bridge construction due to their high torsional stiffness and cost-effectiveness. This study analyzes the structural capacity of a prestressed concrete box girder bridge planned to span the Siak River in Pekanbaru City, consisting of a 97.5 meters main span and two side spans of 58.5 meters each. The bridge is constructed using the balanced cantilever method, allowing for a variable-depth girder profile to optimize performance during the construction stage. Structural analysis was carried out in both transverse and longitudinal directions using the finite element method. The analysis results show that the maximum prestress loss reached 272.22 MPa, equivalent to 19.94% of the initial prestressing stress. Stress evaluations at transfer and service stages were within the allowable limits specified by RSNI-T12-2004. Maximum deflections observed in the side and main spans were 33.21 mm and 80.89 mm, respectively, remaining within serviceability limits. The calculated ultimate capacities for bending, torsion, and shear were 1.20 × 106 kN.m, 3.36 × 104 kN.m, and 4.70 × 104 kN.m, respectively. These results confirm that the designed box girder structure fulfills both strength and serviceability requirements in accordance with national bridge design standards.