Crack Development In Structures Research Articles

РАСЧЕТ КИРПИЧНОГО ПРОСТЕНКА МЕТОДОМ ПРИВЕДЕННЫХ МАТЕРИАЛОВ

Nowadays, the calculation of masonry structures is based on studies and experiments of the past without taking into account the mechanical characteristics, which leads to overestimation or underestimation of the bearing capacity. Such an error affects the formation and development of cracks in structures. To solve this problem, it is necessary to develop a methodology for calculating brickwork, taking into account the mechanical characteristics of its components. The purpose of this work is the numerically simulation and calculation of masonry structures by the method of homogenized characteristics of material on the example of a brick partition. As the object of research, the authors selected brick partition of the building on Zhukovsky Street, 28 in Tyumen. The subject of the study is the stress-strain state of the brickwork. The study was performed based on analytical calculation and numerical simulation in PC ANSYS and PC Lira. As a result, a method of calculating brickwork using the method of homogenized material characteristics has been developed. The scope of application of the results is industrial and civil construction of buildings from masonry structures.

Impact on Strength of Concrete by Coconut Coir and Polypropylene Fibers

Plain concrete is tough in terms of compression and feeble in tension, which leads to development of cracks in structure. The internal micro cracks in concrete which are formed due to tensile stresses, can be minimized and prevented by the addition of fibers in concrete. This project aims at the enhancement of concrete properties with the intrusion of hybrid fibers, by controlling the effect of cracks. The dosages of fibers are 0%, 1%, 2%, 3%, 4% to the weight of cement. The hybrid fibers used in this work are the combination of synthetic fiber of polypropylene twines of 1 to 2 cm and natural fiber of coconut coir of length 2 to 3 cm. The specimen made up of hybrid fibers and conventional concrete are tested for engineering properties like compressive, split-tensile, flexure strength. A comparative study is done between hybrid concrete and conventional concrete.

Study of Flat Slabs Strengthening against Punching Shear

The paper focuses on punching shear strengthening of flat slabs. In the study, different, in practice commonly used systems of strengthening are introduced, systems used less frequently are also mentioned. Chosen methods of strengthening are modeled using FEM software considering material nonlinearity and crack development in structures. 3D models with brick finite elements and discrete modeling of reinforcement are used. The way of modeling of the structure itself is verified against known results of tests of concrete slabs under punching shear. Comparison of individual systems of strengthening is performed from the viewpoint of absolute value of punching shear resistance and it is supplemented by calculation of punching shear resistance according to design code EC 1992. Simultaneously, results are compared to the approach of Critical Shear Crack Theory that places great emphasis on deformation capacity of the slab itself, which can be easily determined from FEM models which allow for material nonlinearity.

Optical fiber sensing of small cracks in isotropic homogeneous materials

Monitoring of cracks and other damages is an integral part of ongoing research. Cracks and other damages may destroy the integrity of structures and even cause engineering accidents. Hence, it is of utmost importance to monitor the development of cracks in structures well in time to restrict the extent of overall damage. In this paper, a novel fiber optic sensor is discussed; this sensor is developed to monitor small cracks (crack openings between 0 and 0.8mm). The sensing principle of the sensor is first introduced and then the influence of dimensional parameters on the sensor is discussed through experimental investigations. The test results indicate that the sensor has a good initial perception capacity and a high sensitivity. Furthermore, the sensor is very effective in monitoring of small cracks.

CONSOLIDATION OF DISTURBED AND UNDISTURBED CLAY AND DIFFERENTIAL SETTLEMENT OF BUILDINGS

Differential settlement of foundations stimulates the development of cracks in structures. However different rate of settlements could be the reason of cracks. The highest rate of settlement takes place during the consolidation period. Theoretical calculations and experimental data showed that rate of settlement of disturbed soil is higher in comparison with undisturbed soil. During the loading of undisturbed soil with structural links displacement of particles and pore pressure dissipation are slower. Pore pressure dissipation begins only after the structural links are broken, ie after the additional stress becomes higher than preconsolidation pressure. The process of disintegration of structural links is slow, therefore the rate of consolidation settlement is also slow. If there are zones of disturbed clay within the layout of building, differential settlement of building can occur. Parameters which are necessary for estimation of the primary consolidation rate of disturbed soil could be calculated using compression curve of the same soil drawn in the semi-logarithmic scale. According to the results of investigations the method described above could be used to predict the rate of primary consolidation of foundations.

CONSOLIDATION OF DISTURBED AND UNDISTURBED CLAY AND DIFFERENTIAL SETTLEMENT OF BUILDINGS

Summary Differential settlement of foundations stimulates the development of cracks in structures. However different rate of settlements could be the reason of cracks. The highest rate of settlement takes place during the consolidation period. Theoretical calculations and experimental data showed that rate of settlement of disturbed soil is higher in comparison with undisturbed soil. During the loading of undisturbed soil with structural links displacement of particles and pore pressure dissipation are slower. Pore pressure dissipation begins only after the structural links are broken, ie after the additional stress becomes higher than preconsolidation pressure. The process of disintegration of structural links is slow, therefore the rate of consolidation settlement is also slow. If there are zones of disturbed clay within the layout of building, differential settlement of building can occur. Parameters which are necessary for estimation of the primary consolidation rate of disturbed soil could be calcula...

BISPECTRAL ANALYSIS OF THE BILINEAR OSCILLATOR WITH APPLICATION TO THE DETECTION OF FATIGUE CRACKS

Damage detection by means of non-destructive testing plays an important role in ensuring the integrity of machine elements and structures. Vibration testing is an effective means of detecting crack development in structures. In this paper the effect of crack closure on the dynamic behaviour of cantilever beams is studied. Since the crack opens or closes depending on the direction of the vibration, the beam exhibits bilinear characteristics. The aim of the paper is to analyze the system response by using bispectral analysis which forms a subset of higher order statistical analysis. The study has been conducted both on simulated and experimental vibration signals. Firstly, a simplified model is employed to simulate the bilinear behaviour of a beam with a closing crack. The model is an oscillator with a bilinear restoring forcing function. The analysis of the forced vibrations of the model is performed by means of the harmonic balance method showing the occurrence of harmonics in the response spectrum which are strictly related to the bilinear nature of the model. Moreover, an experimental test carried out on a straight beam with a fatigue crack is presented. The beam is excited with white noise by means of a vibration shaker. The bispectral analysis performed both on the model and the actual structure shows high sensitivity of the non-linear behaviour of the system: that is to say, to the presence of the fatigue crack in the structure. In particular, the interactions between the frequency components contained in the signal response are analyzed. The results provide a possibility of using the bispectral analysis technique to detect damages in structures.