PSI - Issue 65

I. Shardakov et al. / Procedia Structural Integrity 65 (2024) 233–240 I. Shardakov, R. Tsvetkov, I. Glot, A. Shestakov, G. Gusev, V. Yepin / Structural Integrity Procedia 00 (2024) 000–000

234

2

1. Introduction

Monitoring the deformation state of critical engineering and building structures is an important engineering task. Its solution in modern conditions is carried out using automated deformation monitoring systems that perform online spatio-temporal registration of deformation processes in structural elements. One of the main tasks of monitoring is a timely forecast of the possibility of a critical deformations occurring in a structure or in any of its elements, which can violate its integrity. The solution to this problem is carried out on the basis of a set of data received by the analytical block of the monitoring system from various sets of primary sensors that record various parameters, such as relative displacements and rotations of structural elements; vibration processes; temperature changes, etc. But the effectiveness of monitoring increases significantly if it is possible to control the parameters that respond to early precursors of the transition of structural elements to an inelastic state and control these parameters during the operation of the structure. From the works of Grosse (2008) it is known that one of the methods that could solve this problem is the acoustic emission (AE) method. This method is based on recording acoustic signals that are generated when the continuity of the material is broken or when the material goes into an inelastic state during the deformation of the structure. Analysis of acoustic signals against the background of operational loads of the structure allows us to record the level of inelastic deformation and determine its localization, as well as determine the type, density and kinetics of accumulation of microdefects in the material that form inelastic deformation. Ohno (2010) and Aggelis (2011) proposed an approach to analyze the parameters of AE signals for reinforced concrete. In most of these studies, laboratory samples with characteristic dimensions of about 10 cm were used to study AE, in which a homogeneous stress-strain state was realized at the macro level. The conducted studies made it possible to establish a number of important patterns linking the kinetics of AE signals with the onset of the initial stage of inelastic deformation and the development of the final phase of destruction. There is a significant number of works in which the AE method was used in experiments with individual elements of concrete building structures such as columns, slabs, and crossbars. In these studies, the scale and size of the structure showed itself to be a significant factor. It has been shown that AE signals decay rapidly with distance and a noticeable change in signal parameters occurs. Aggelis (2015), Zhang (2020 and 2022) have shown that it is possible to extract useful information from AE signals at distances of 0.8 m and 1.5m from the source, respectively. To assess the capabilities and effectiveness of using the AE method on real reinforced concrete structures, it is necessary to conduct experiments on structures of the same scale or their analogues. This is due to the fact that in real structures, the deformation interaction of structural elements of different scale and properties and their complex mutual spatial arrangement significantly affects the propagation of AE signals. The problems of such studies for large-scale structure are reflected in the works of Thirumalaiselvi (2021) and Guo (2023). The purpose of this work is to evaluate the possibility of using the AE method to record the inelastic deformation of elements of a large-scale model reinforced concrete structure under local force loading with the formation of cracks. To realize the experiments on elastic and inelastic deformation of a model reinforced concrete structure by local force loading, we used the experimental stand presented in Figure 1a. The design and technical capabilities of the stand were described in detail in the works Shardakov et al (2018 and 2020). The tested structure is a 4-story building made of monolithic reinforced concrete, consisting of 24 cells of the same type (Fig. 1a). It is an image of a typical building structure on a scale of 1:2. The length of the structure is 6 m, width 4 m, height 6 m; the size of the model cell is as follows: length 2 m., width 2 m., height 1.5 m. The columns have cross-sectional dimensions of 0.2×0.2 m, and the crossbars 0.2×0.1 m. The thickness of the floor slab is 0.15 m. Figure 1b shows a fragment obtained by cutting a model structure with a vertical plane passing through the longitudinal central row of columns. The external force is applied using a hydraulic jack installed between the 2nd and 3rd floors (Fig. 1b). Diaton sensors with a frequency range 30–120 kHz and a gain of 34 dB were used to record AE signals. The location of 4 acoustic emission sensors are shown in Fig. 1b. Signals from sensors were recorded using ADC cards with 14 bits and sampling frequency f s = 2.5 MHz. Data recording from 4 sensors was performed on one computer 2. Model structure and structural scheme of the experiment