PSI - Issue 28

I. Shardakov et al. / Procedia Structural Integrity 28 (2020) 1407–1415 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Keywords: concrete structure; larde-scale model, experiment, inelastic deformation, damage; vibration diagnostics, acoustic emission

1. Introduction Experimental studies of critical deformations in reinforced concrete structures help to understand the essence of mechanical processes occurring in them and to assess how long they can withstand the applied load. A characteristic feature of these structures is that they consist of the elements of different sizes (slabs, columns, beams, etc.) interacting with each other. Testing of individual fragments of such structures cannot reproduce the whole variety of deformation processes in the structure as a whole. This is especially true when structural elements pass from elastic state to inelastic one and damages arise and develop in separate parts of the structure. Therefore, it is necessary to study critical deformation processes in complex reinforced concrete structures using the samples that are close in scale and design features to real prototype. Testing of large-scale building structures is performed most often when studying the behaviour of such objects under conditions of seismic loads. These investigations are mainly concerned with observation of the movement of structural elements under conditions of high amplitude dynamic loads, the analysis of the crack formation and propagation, and recording of scenarios of damage accumulation and failure, Toma and Atanasiu (2010), Garcia et al. (2014). The information obtained is used to solve the problems of seismic resistance of existing and newly constructed structures. Nowadays laboratory testing of large-scale objects under conditions of static or slowly changing external loads is of increasing interest among researchers. Such processes occur in structures under the action of operational loads, as well as due to changes in the state of foundations caused by karst effects, freezing of soils, and various technogenic processes in the surrounding soil massif. Laboratory tests of full-size reinforced concrete fragments under static and quasi-static loads are described in Frolov (2019), Kim and Choi (2016). Bench tests simulating the interaction of large scale models of engineering structures with subgrade soil are reviewed in Al Heib et al. (2013), Sarhosis et al. (2019), Wu, Ketchart and Adams (2008). The main attention in these works is focused on the description of the observed scenarios of damage evolution, detection of the most vulnerable structural elements and ascertaining whether the deformation state of the structure complies with building codes. However, the problem of identifying the destruction precursors and the development of methods for recording early signs of damage remains insufficiently studied. From a practical point of view, it is extremely important to assess the operability of structures with a certain level of accumulated damage. The study of these problems provides a basis for the development of effective automated monitoring systems that ensure reliable and safe operation of controlled object. 2. Model object and experimental design Currently, a large-scale experiment is carried out at the Institute of Continuum Media Mechanics, Perm, Russia. The experiment is aimed at studying the deformation behavior of a large-scale model reinforced concrete structure under conditions of quasistatic loading. The main objective is to trace the change in the mechanical state of the structure over its entire life cycle (from the initial elastic state to failure) on the basis of the results of vibration diagnostics and acoustic emission. Under experimental conditions, such processes as contact interaction of structural parts, binding of structural elements due to steel reinforcement, real material composition, etc., are reproduced. This paper presents the first results of the experiments simulating the deformation response of structural elements to the local quasi-static and impulse loads. The experimental sample is a fragment of a precast-monolithic building on a scale of 1:2, including 24 standard cells combined into a 4-storey structure. The experimental sample was designed based on the results of numerical simulation of the deformation processes in it, from an elastic state to inelastic one, Shardakov et al (2018). Dimensions of the sample are as follows: length 6m, width 4m, height 6m, and the size of a typical cell is 2×2×1.5m. The bearing columns and crossbars have a cross section of 20×15 cm, and 20×25 cm, respectively; floor slab thickness is 15 cm, and the diameter of the reinforcement is 12 mm and 8 mm. Figure 1a represents a half of the model building with sensors placed on it. Static loading of the sample is carried out by applying a local self-balanced force F s generated by a jack installed between the 2nd and 3rd levels (red arrow). The response of the model structure to localized static load