Abstract
Safety and reliability of constructions operated are predicted using the known mechanical properties of materials and geometry of cross-sections, and also the known internal forces. The extensometry technique (electro-resistant tensometers, wire gauges, sensor systems) is a common method applied under laboratory conditions to determine the deformation state of a material. The construction sector rarely uses ultrasonic extensometry with the acoustoelastic (AE) method which is based on the relation between the direction of ultrasonic waves and the direction of normal stresses. It is generally used to identify stress states of machine or vehicles parts, mainly made of steel, characterized by high homogeneity and a lack of inherent internal defects. The AE effect was detected in autoclaved aerated concrete (AAC), which is usually used in masonry units. The acoustoelastic effect was used in the tests described to identify the complex stress state in masonry walls (masonry units) made of AAC. At first, the relationships were determined for mean hydrostatic stresses P and mean compressive stresses σ3 with relation to velocities of the longitudinal ultrasonic wave cp. These stresses were used to determine stresses σ3. The discrete approach was used which consists in analyzing single masonry units. Changes in velocity of longitudinal waves were identified at a test stand to control the stress states of an element tested by the digital image correlation (DIC) technique. The analyses involved density and the impact of moisture content of AAC. Then, the method was verified on nine walls subjected to axial compression and the model was validated with the FEM micromodel. It was demonstrated that mean compressive stresses σ3 and hydrostatic stresses, which were determined for the masonry using the method considered, could be determined even up to ca. 75% of failure stresses at the acceptable error level of 15%. Stresses σ1 parallel to bed joints were calculated using the known mean hydrostatic stresses and mean compressive stresses σ3.
Highlights
The ultrasonic technique [1,2,3,4] is used in spectroscopy, defectoscopy, evaluation tests, coagulation, dispergation, sonoluminescence cavitation, and chemical reactions
This paper describes the tests aimed at determining the complex state of stresses in masonry units made of autoclaved aerated concrete
The test results for nine masonry models under axial compression, described in [11], were used in the stage II to determine at first mean hydrostatic stress, and the normal stress σ1 which was parallel to the plane of bed joints
Summary
The ultrasonic technique [1,2,3,4] is used in spectroscopy, defectoscopy, evaluation tests, coagulation, dispergation, sonoluminescence cavitation, and chemical reactions. Ultrasounds can be applied to crush, form hard media, bond, solder, wash, extract, and dry substances Another important application of these ultrasonic techniques includes stress measurements in metal constructions. This paper describes the tests aimed at determining the complex state of stresses in masonry units made of autoclaved aerated concrete. As in [11], verification tests were performed on small parts of the wall subjected to axial compression Their aim was to define empirical relationships of mean hydrostatic stresses P, and normal stresses σ1 and σ3 in the wall, in which the AE effect was observed [12]. Stage II included nine wall models [11] made of AAC masonry units which had a nominal density of 600 kg/m3 They were subjected to axial compression The velocity of ultrasonic wave cp in the masonry units was measured. Knowing stress values σ3 determined in [11], the levels of normal stress σ1 could be determined
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