Damage fracture characterization of reinforced concrete beam subjected to four-point bending with parametric analysis of static,dynamic,and acoustic properties

The aim of this study is to clarify the damage fracture process using acoustic emission technique and construct relationships between acoustic emission parameters and static, dynamic properties of reinforced concrete beam under four-point bending. Laboratory experiments were performed on two reinforced concrete beams with same length 250 cm. Static parameters including crack and displacement patterns with load level were observed and analyzed. Acoustic emission parameters of hit, count, amplitude, energy, duration, index of damage, and b-value with the increase in damage were demonstrated and corresponded to observed crack status of structure, which realized the damage process classification and mechanism characterization. Correlations of acoustic emission parameters and cumulative crack width with the first-order natural frequency were obtained to clarify their relevance. The results revealed that as the level of damage increased, the values of cumulative acoustic emission parameters increased, which could classify the damage fracture process into four stages. And the results coincided with the observed crack and displacement patterns of reinforced concrete beam. Sum of maximum width for observed cracks presented favorable quadric relations with acoustic emission parameters. Index of damage and b-value analyses (classical and Gaussian filtered ones) demonstrated the crack characteristic at each load step, which were in accordance with the observed crack patterns. Change rate of the first-order natural frequency presented favorable cubic relationships with acoustic emission energy and hit, while linear and negative relations with sum of crack widths. The results obtained in this study can be used for damage fracture characterization and health monitoring of reinforced concrete structures subjected to flexural load.