Abstract:

On the basis of fictitious crack model, an analytical method to calculate the fracture toughness of reinforced concrete was proposed under reasonable hypothesis by analyzing the mechanical characteristics at the cracked section of a specimen in three-point bending. The method was used to calculate the maximum load, critical effective crack length and in turn the fracture toughness of reinforced concrete beams in three-point bending whose  α₀ (ratio of initial crack length to specimen height) were 0.2, 0.3, 0.4 and 0.5 respectively. The maximum error of unstable fracture toughness was 4.951% by comparing calculation results with test data. The results indicated that the method could predict the unstable fracture toughness precisely. Furthermore, the impact of  α₀ on the unstable fracture toughness was studied. It was found that the unstable fracture toughness generally did not vary with α₀, thus could be regarded as material constant to determine whether a crack will propagate.  

Key words:  reinforced concrete, unstable fracture toughness,  initial crack height ratio, maximum load