Structural behaviour and failure mechanisms of Gerber half-joints through experimental analyses

The assessment of the Gerber half-joints (or saddles) is today a topical problem since these structural elements, classified as "critical" by the recent Italian guidelines, are widespread in the infrastructure heritage of different countries. The paper presents the results of an experimental research aimed at evaluating the non-linear behaviour of Gerber half-joints up to failure. Four reinforced concrete Gerber half-joints were designed, cast and tested at the Laboratory of the University of Rome “Tor Vergata”. Particular care was devoted to the design phase of the specimens, in order to achieve the desired failure modes. Two steel ties layouts and two reinforcement amounts are considered to understand the effects of steel detailing and to account for failure involving steel rebars rupture or concrete struts collapse. The test set-up and the measure instrumentation were suitably designed and placed for providing experimental data useful for a better comprehension of the influence of the reinforcement amount and layout on the structural response, and on the failure mechanisms. The experimental evidence is also interpreted in the light of the classical strut and tie analytical model, in the view of the assessment of existing structures. Furthermore, the potential of the Digital Image Correlation technique in detecting the initial crack and the progression in the mechanism, is discussed.