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

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.