Experimental and analytical investigation of the crack behaviour of dapped-end beams

Abstract

Reinforced concrete dapped ends are a widely used connection for precast elements in infrastructure and building structures. However, they are prone to major durability problems due to the formation of an inclined crack at the re-entrant corner of the joint. The crack typically forms at low loads and reaches a significant opening under service load conditions, causing corrosion and stress concentration in the reinforcement, which impairs the safety of the connection. The behaviour of these cracks in a highly disturbed structural region is not well understood. This paper presents the experimental results of 28 dapped-end tests in which the crack behaviour in the re-entrant corner was continuously measured using digital image correlation. The main test variables are the amount of dapped-end reinforcement, the presence of diagonal reinforcement and the ratio of horizontal to vertical dapped-end reinforcement area. The bond behaviour of the dapped-end reinforcement was estimated from the measured crack widths and reinforcement strains, assuming a pull-out mechanism with constant bond shear stresses on both crack sides. The paper proposes a model for evaluating the width of corner cracks at service loads, in which the reinforcement strains are derived from strut-and-tie models. The modelling results agreed satisfactorily well with the experimental observations of this study and 28 additional tests from the literature for dapped-ends with reinforcement diameter below 20 mm.