Nonlinear FEM Analysis of Prestressed Gerber Beam Bridges: Shear assessment of A Highway Infrastructure Case Study

This thesis, developed in collaboration with SINA S.p.A. of the ASTM Group, investigates the structural adequacy of prestressed Gerber beam bridges constructed during Italy’s 1970s highway infrastructure expansion. The research focuses on the critical shear assessment of girder beam end half-joints, which exhibit insufficient transverse reinforcement according to contemporary design standards. A comprehensive comparative analysis between 1970s design codes and current Italian technical standards (NTC2018, DM 578- Linee Guida Ponti) reveals significant discrepancies in shear reinforcement requirements, with conventional verification procedures indicating substantial structural deficiencies for many existing bridges. The study develops advanced nonlinear finite element methodologies using ANSYS software to accurately simulate the complex stress distribution patterns within these critical structural elements. Particular attention is devoted to disturbed regions (D-regions) where geometric discontinuities create stress concentrations, employing strut-and tie modeling principles integrated within a sophisticated computational framework. The local finite element model is validated through a dual verification procedure: analytical verification using a simplified global LUSAS model and nonlinear analysis of an extended beam portion. Results demonstrate that nonlinear analysis, accounting for material plastic capacity and stress redistribution, confirms adequate shear structural capacity under design loads, contradicting the deficiencies predicted by conventional linear elastic assessments. The findings have significant implications for infrastructure management, suggesting that many bridges flagged for strengthening may actually possess sufficient structural capacity. This supports development of optimized assessment procedures that could substantially reduce strengthening interventions, enabling more cost-effective infrastructure management strategies.