Structural behavior of deteriorated Gerber half‐joints in highway overpasses by nonlinear finite element analysis combined with a simplified uniform‐corrosion model

Abstract Gerber half‐joints, broadly used in the last century as elements of concrete bridges, are prone to corrosion‐induced deterioration, which may lead to brittle shear collapse. It is of paramount importance to develop advanced numerical models for simulating the collapse behavior of Gerber half‐joints, taking material deterioration into account. This paper investigates the ultimate capacity of deteriorated Gerber half‐joints belonging to a set of 50‐year‐old road overpasses in Messina, Italy. The peculiarities of these prestressed concrete bridges are: (1) oversized hangers and diagonal reinforcement bars in the dapped end; (2) inadequate concrete compressed area in the section above the pier subject to negative bending moment. Calibrated upon an extensive in situ test campaign, a parametric 2D and 3D nonlinear finite element analysis (NLFEA) of a portion of the bridge deck is performed to quantify model uncertainties related to: (i) modeling approach, involving different dimensions of the finite element (FE) model (2D and 3D), software, solvers, and implemented nonlinear concrete material model; (ii) shrinkage and creep formulation in the NLFEAs; (iii) effect of the transverse diaphragm in the section above the pier. Carbonation depths identified from experimental tests in conjunction with gravimetric analysis on extracted steel samples are used for calibrating a simplified uniform‐corrosion model, which is incorporated in the NLFEA to investigate the influence of corrosion on the load‐bearing capacity and failure mechanism of the investigated Gerber half‐joints. It is found that the load‐bearing capacity is negligibly reduced (<2%) by the corrosion penetration at the current date (53 years from the construction) and moderately decreases (around 10%) at 100 years of service life. NLFEA outcomes are finally compared to simplified formulations based on strut‐and‐tie models and cross‐sectional analyses to estimate discrepancies resulting from different levels of approximation, as suggested by modern design codes.