R. Vidya Sagar

A review of recent developments in parametric based acoustic emission techniques applied to concrete structures

This article presents a review of recent developments in parametric based acoustic emission (AE) techniques applied to concrete structures. It recapitulates the significant milestones achieved by previous researchers including various methods and models developed in AE testing of concrete structures. The aim is to provide an overview of the specific features of parametric based AE techniques of concrete structures carried out over the years. Emphasis is given to traditional parameter-based AE techniques applied to concrete structures. A significant amount of research on AE techniques applied to concrete structures has already been published and considerable attention has been given to those publications. Some recent studies such as AE energy analysis and b-value analysis used to assess damage of concrete bridge beams have also been discussed. The formation of fracture process zone and the AE energy released during the fracture process in concrete beam specimens have been summarised. A large body of experimental data on AE characteristics of concrete has accumulated over the last three decades. This review of parametric based AE techniques applied to concrete structures may be helpful to the concerned researchers and engineers to better understand the failure mechanism of concrete and evolve more useful methods and approaches for diagnostic inspection of structural elements and failure prediction/prevention of concrete structures.

Evaluation of damage in reinforced concrete bridge beams using acoustic emission technique

Acoustic emission (AE) testing is a well-known method for damage identification of various concrete structures including bridges. This article presents a method to assess damage in reinforced concrete (RC) bridge beams subjected to incremental cyclic loading. The specifications in the standard NDIS-2421 were used to classify the damage in RC bridge beams. Earlier researchers classified the damage occurring in bridge beams by using crack mouth opening displacement (CMOD) and AE released and proposed a standard (NDIS-2421: the Japanese Society for NonDestructive Inspection). In general, multiple cracks take place in RC beams under bending; therefore, utilisation of CMOD for crack detection may not be appropriate. In the present study, the damage in RC beams is classified by using the AE released, deflection, strains in steel and concrete, because the measurement of the strains in steel and concrete is easy and the codes of practice are specified for different limit states (IS-456:2000). The observations made in the present experimental study have some important practical applications in assessing the state of damage of concrete structural members.

Modelling heterogeneity of concrete using 2D lattice network for concrete fracture and comparison with AE study

In this paper, numerical modelling of fracture in concrete using two-dimensional lattice model is presented and also a few issues related to lattice modelling technique applicable to concrete fracture are reviewed. A comparison is made with acoustic emission (AE) events with the number of fractured elements. To implement the heterogeneity of the plain concrete, two methods namely, by generating grain structure of the concrete using Fuller’s distribution and the concrete material properties are randomly distributed following Gaussian distribution are used. In the first method, the modelling of the concrete at meso level is carried out following the existing methods available in literature. The shape of the aggregates present in the concrete are assumed as perfect spheres and shape of the same in two-dimensional lattice network is circular. A three-point bend (TPB) specimen is tested in the experiment under crack mouth opening displacement (CMOD) control at a rate of 0·0004 mm/sec and the fracture process in the same TPB specimen is modelled using regular triangular 2D lattice network. Load versus crack mouth opening displacement (CMOD) plots thus obtained by using both the methods are compared with experimental results. It was observed that the number of fractured elements increases near the peak load and beyond the peak load. That is once the crack starts to propagate. AE hits also increase rapidly beyond the peak load. It is compulsory here to mention that although the lattice modelling of concrete fracture used in this present study is very similar to those already available in literature, the present work brings out certain finer details which are not available explicitly in the earlier works.

Balanced Energy Dissipation at Propagating Crack Tip in Quasi-Brittle Materials? - Analysis via Soft-Computing Methods

Analysis on the aspects of the energy dissipation in the case of quasi-brittle fracture is presented. Dissipation both via cohesive forces at the crack faces and the one taking place within the volume of the fracture process zone is considered. Tools from the field of soft computing techniques are employed. The analysis is conducted on results from extensive experimental campaign.

Verification of the applicability of the Gaussian mixture modelling for damage identification in reinforced concrete structures using acoustic emission testing

AbstractThis article presents an experimental study on verification of the applicability of Gaussian mixture modelling (GMM) algorithm of acoustic emissions for damage identification in reinforced concrete (RC) structures. Eight RC-flanged beam specimens with different properties were tested subjected to flexural loading. An incremental cyclic load was applied on RC-flanged beam specimens till failure, and simultaneously, the released acoustic emissions (AE) were recorded. It may be required to study crack classification in RC structures, because crack classification studies are useful to predict the structural performance and subsequently to implement the appropriate structural rehabilitation methods. AE belonging to tensile cracking and shear cracking can be studied by a probabilistic approach. It was observed that the line separating the AE clusters belonging to tensile and shear cracks was shifting towards a higher rise angle as the specimen is reaching collapse stage. This observation indicates dominance of shear cracks near the collapse stage. At the loading cycle where yielding occurred in the test specimen obtained by using GMM algorithm for AE, the load cycle entered into heavy damage zone is almost same as per NDIS-2421 damage assessment chart. The results obtained by both GMM algorithms for AE and NDIS-2421 criterion to evaluate the damage in the RC-flanged beams were compared and discussed.

Acoustic Emission During Flexural Deformation of Reinforced Concrete Under Incremental Cyclic Loading

Acoustic emissions (AE) released during the flexure tests of reinforced concrete (RC) beams under incremental cyclic loading conditions in the laboratory were subjected to improved b-value (Ib-value) analysis. Ib-value has been reported to be useful to detect, track, and investigate the various stages of micro-cracking and macro-crack damage in concrete. Further, Ib-value has been found to be free from the influence of monitoring conditions. We observed in the present study that the Ib-value began to decrease with the beginning of the formation of new micro-cracks, and then stabilized (similar to 1.0) and finally dropped down sharply to a very low value marking the onset of macro-crack damage and its growth in concrete. Additionally, when the Ib-value decreased, AE with steep rise angle (RA) values were noticed with the formation and growth of micro-cracks in concrete. On the contrary, the average frequency (AF) of AE events was found to decrease during the micro-and macro-cracking stages of the test beams. These experimental observations of AE-based Ib-value combined with RA and AF were useful for the detailed study of flexural deformation and the failure of concrete at various stages in the laboratory and, perhaps, in situ conditions as well.

7 – Laboratory investigations on concrete fracture using acoustic emission techniques

This chapter presents laboratory investigations on concrete fracture using acoustic emission (AE) techniques. It recapitulates the studies done by previous researchers related to parametric-based AE techniques, which were applied to study the fracture parameters of concrete structures in a laboratory. AE energy analysis, b-value analysis, and classification of cracking in concrete structures have been discussed. Laboratory investigations on concrete fracture using AE techniques could be helpful for concerned researchers and engineers to understand the fracture process in concrete better and to evolve more useful methods, in addition to diagnostic approaches for inspection of structural elements and failure prediction/prevention of concrete structures.