Laboratory investigations on cracking in reinforced concrete beams using on-line acoustic emission monitoring technique
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ORIGINAL PAPER
Laboratory investigations on cracking in reinforced concrete beams using on-line acoustic emission monitoring technique R. Vidya Sagar • B. K. Raghu Prasad
Received: 27 September 2012 / Revised: 8 January 2013 / Accepted: 10 January 2013 / Published online: 2 February 2013 Ó Springer-Verlag Berlin Heidelberg 2013
Abstract This article presents an experimental study on variation in acoustic emission (AE) parameters during cracking in reinforced concrete (RC) beams subjected to incremental cyclic loading in laboratory conditions. Nine RC beams with three different span-to-depth ratios ranging from 2.0 to 6.0 with a reinforcement ratio roughly kept the same (1.4–1.5 %) were tested under bending till failure and simultaneously the released AE was recorded. The criteria used to characterize the cracking in RC beams are based on the AE parameters. The AE parameters such as frequency, duration, amplitude, count, rise time, parameters depending on AE signatures such as b-value, and damage parameter D follow the fracture process during the entire loading. The results are useful to distinguish different cracks in RC beams and extend them for field applications. Keywords Acoustic emission Reinforced concrete Fracture Crack classification Notations AE Acoustic emission AF Average frequency RA Rise time D Damage parameter RC Reinforced concrete
R. Vidya Sagar (&) Department of Civil Engineering, Indian Institute of Science, Bangalore 560 012, India e-mail: [email protected] B. K. Raghu Prasad Centre for Campus Maintenance and Development, Indian Institute of Science, Bangalore 560 012, India
1 Introduction The formation and growth of cracks in RC structures lead to critical structural consequences. Generally, cracks develop mainly due to bond failure between coarse aggregate and cement matrix [1–4]. The primary cause for failure of RC structures is attributed to crack development. There are various reasons for the development of cracks in RC structures. The reasons are grouped as due to mechanical loading and due to environmental factors. It is known that cracks develop in RC structures due to various reasons like application of heavy loads, corrosion of steel in RC structures, temperature variations, sub-grade settlement, and earthquakes. Researchers give importance to study the fracture process in concrete because cracking affects the integrity of the structure [1–4]. It is known that flexural (tensile) cracks are more ductile, whereas shear cracks are more brittle and may lead to sudden failure. The cause and location of cracks is crucial to determine which type of crack is predominant and whether the RC structure requires immediate rehabilitation or not. The width of the crack is an important issue along with its location in the structure. In case the crack width is more than specified by the codes of practice, rehabilitation of the structure is required [1–4]. Therefore, a proper identification of the extent and cause of cracking is to be done to implement a suitable rehabilitation of the RC struc
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