PSI - Issue 84

Beatrice Baldan et al. / Procedia Structural Integrity 84 (2026) 569–574

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stress distributions, limited redundancy, and reinforcement detailing, often leading to brittle and sudden failure modes. Recent bridge collapses have further emphasized the vulnerability of these components, particularly in aging infrastructures affected by material degradation and corrosion (di Prisco et al.2023, Xinchen Z et al. 2022). The assessment of Gerber half-joints in existing bridges is especially challenging due to difficulties in inspection, limited accessibility, and the lack of reliable information on reinforcement layout and material properties. From a mechanical standpoint, half-joints are classified as discontinuity regions (D-regions), where the stress field cannot be described by classical beam theory (Schlaich J et al. 1987). Strut-and-tie (S&T) models therefore represent a widely adopted approach for their structural assessment, as they provide a rational framework for describing force transfer mechanisms in reinforced concrete D-regions (En 1992-1-1). However, conventional S&T formulations, typically calibrated for design purposes, may not be directly applicable to existing half-joints, particularly when deterioration, distributed reinforcement, or non-ideal detailing are present (Granata et al. 2023). Experimental investigations reported in the literature have shown that the ultimate capacity of half-joints is highly sensitive to reinforcement anchorage, hanger reinforcement, and the interaction between compressive struts and tensile ties, which may lead to some differences between experimental outcomes and simplified analytical predictions. Finite Element (FE) modeling has also been widely adopted for the analysis of reinforced concrete half-joints, showing satisfactory agreement with experimental results in controlled conditions (Boothman et al. 2008). However, the application of FE approaches to existing bridges is often limited by the need for extensive calibration of constitutive models and interface parameters, whose values are difficult to identify through in situ investigations. Moreover, FE analyses are computationally demanding and highly sensitive to assumptions regarding material properties, cracking behavior, bond–slip relationships, and reinforcement detailing, which are frequently unknown in existing structures. These aspects reduce their reliability and practical applicability for routine assessment, especially when a limited amount of information is available. Within this context, the present study investigates the reliability of assessment methodologies commonly adopted in engineering practice for the evaluation of Gerber half-joints. A comparative analysis is performed between experimental results available in literature and analytical estimates obtained through strut-and-tie models developed in a computational environment, considering both elastic and plastic behavior. The results highlight cases of good agreement as well as significant overestimations of the ultimate capacity, underlining the necessity of adequately accounting for both compressive and tensile mechanisms. The study aims to provide insight into the strengths and limitations of current assessment approaches and to support more reliable structural evaluation of Gerber half-joints in existing bridge infrastructure.

Half-joint

Upper nib

Bearing

Lower nib

Figure 1 Identification of the half joint

2. Experimental results overview As a preliminary step to validate the proposed methodologies, results from experimental campaigns available in the literature were collected and analyzed, such as ultimate load, cracking angle, material properties (mean values), reinforcement layout, failure modes. All dapped-end beams were tested under vertical load only. The campaigns were conducted by Desnerck et al. (2016), Di Carlo et al. (2023), Lu et al. (2012), Mata-Falcon (2019), Ferreira et al. (2023),