Experimental research on reinforced concrete dapped-end beams: shear strength and serviceability behaviour

摘要

Dapped-end beams are currently a common end in concrete structures, particularly in the field of precast concrete manufacturing. However, unacceptable diagonal cracks frequently occur at service loads in the vicinity of the re-entrant corner. There is a lack of experimental data and knowledge on the behaviour of dapped-end beams under service loads; the aim of this research is to analyze the influence of different variables on the crack width in dapped-end beams, such as the layout of steel bars, the amount of diagonal reinforcement and the geometric shape of the re-entrant corner. An experimental program is carried out on 18 dapped-end beams with 3.00 m length and a cross-section of 25×60 cm, reduced to 25×30 cm at the ends. Experimental results help to conclude that dapped-end beams are usually conditioned by cracking service limit state instead of ultimate state (load-bearing capacity). Smaller crack width is observed in specimens with diagonal reinforcement than those with only orthogonal reinforcement; increasing the amount of the diagonal reinforcement regarding to the orthogonal one, greater effect in reduction of crack width occurs. Change in geometric shape bevelling the re-entrant corner also leads to crack reduction.