Structural Behaviour and Crack Evolution of Full-Scale RC Dapped-End Beams with Orthogonal Reinforcement

Abstract

Ageing reinforced concrete bridges from the 1970s and 1980s increasingly exhibit deterioration in critical structural details, such as dapped-end regions in Gerber-type bridge systems. These regions are prone to early cracking, which accelerates reinforcement corrosion and compromises structural safety. This study presents the first phase of an ongoing research programme investigating the interaction between mechanical loading, sustained loading and corrosion. Full-scale dapped-end beams with varying orthogonal reinforcement layouts were tested under static loading until failure to establish a mechanical reference state. Crack development, load-displacement behaviour and failure mechanisms were monitored , with particular emphasis on service-relevant load levels around 50% of the ultimate capacity. The results show a transition from flexural, reinforcement-controlled behaviour to concrete-governed mixed flexural-shear failure with increasing reinforcement. The findings provide a robust experimental baseline for subsequent long-term creep and corrosion experiments and for validating numerical models. 1 BACKGROUND AND MOTIVATION A significant proportion of reinforced concrete bridge infrastructure in Europe was constructed during the 1970s and 1980s and is now approaching or exceeding its intended service life. Ageing-related deterioration processes such as reinforcement corrosion, concrete cracking and material degradation increasingly threaten structural safety and durability. Recent bridge failures have demonstrated that local weaknesses in critical structural details can trigger global collapse, highlighting the need for improved assessment tools supported by experimentally validated evidence. Well-documented examples include the collapse of the de la Concorde overpass in Canada [1] and the Annone Brianza bridge in Italy [2] One particularly vulnerable structural detail is the reinforced concrete dapped-end (DE) beam, commonly used in Gerber-type bridge systems (Fig. 1). The geometric discontinuity at the dapped end causes highly disturbed stress distributions and pronounced tensile stresses near the re-entrant corner, leading to early crack formation under service loads. These cracks tend to open relatively wide and act as preferential pathways for water and chlorides, accelerating reinforcement corrosion and the associated loss of load-bearing capacity. Field inspections of existing bridges in Belgium and elsewhere frequently reveal severe cracking and advanced corrosion damage in dapped-end regions.