Structural Assessment of Corroded Dapped-end Beams

Many existing concrete bridges with typical cantilever static schemes and with dapped-end suffer deterioration problems due to reinforcement corrosion and concrete degradation. Indeed, such infrastructures have usually reached or are going to reach the end of their service lives, and have been designed with outdated standards, where the durability problems were not considered. Moreover, the design loads used in the past are obsolete, not merely related to the design procedures, but also for increasing magnitudes of traffic and truck weights. In this context, the evolution of degradation of the reinforcement and concrete due to corrosion is particularly relevant, especially concerning the failure modes of the dapped-end beam. In recent decades, some catastrophic events related to the collapse of bridges with dapped-end beams highlighted how these elements are a critical part of such infrastructures. For this reason, their state of conservation must be analysed and evaluated carefully, especially in cases where reinforcement corrosion is present. Over the years, various experimental techniques and analytical methods have been developed for studying dapped-end beams, and current standards provide well-tested tools for the design of these elements, such as the strut-and-tie method. However, the evaluation of existing dapped-end beams presents a separate issue. Due to both their shape and their location in areas that are difficult to access for regular and special inspections, these elements are highly susceptible to significant degradation and corrosion. Assessing the load-bearing capacity of dapped-end beams affected by corrosion is a current and relevant topic. The uncertainties related to reinforcement corrosion and the difficulty of accurately determining the structural degradation make this assessment extremely challenging. Current standards have only recently begun focusing on the development of reliable tools for evaluating existing structures, with limited progress specifically regarding dapped-end beams. In the literature, there are still relatively few studies addressing the issue of residual life assessment for dapped-end beams, particularly concerning corrosion-related aspects, highlighting the lack of a unified or standardized procedure for this type of analysis. In this context, the present study aims to contribute to a correct methodological and engineering approach for evaluating the resistance of existing corroded dapped-end beams. Specifically, the problem of chloride-induced corrosion in dapped-end beams is analysed. The research aims to propose both numerical and analytical methods for assessing the residual structural capacity of corroded and non-corroded dapped-end beams, by adopting nonlinear finite element techniques and a simplified strut-and-tie model for corroded elements. The capacity of corroded dapped-ends is evaluated by considering several corrosion effects, such as mechanical properties decay of steel rebars and concrete as well as deterioration of bond-slip behaviour between steel and concrete. The proposed models have been validated both with and without corrosion using the latest experimental tests. Both the numerical modelling techniques and the analytical method have proven to be adequate and reasonably accurate for assessing the residual capacity of corroded dapped-end beams.