Corrosion of reinforced concrete structures occurs in two stages characterized by different intensities of the corrosion development: the initiation period of the corrosion process and the propagation period of the corrosion process. Consequences of the reinforcement corrosion in concrete are the reduction of the cross-sectional area of the reinforcement bars, and cracking of the concrete cover. The reduction of the reinforcement structural capacity due to the corrosion, over a sufficiently long period of time, may result in structural failure of the designed structural element. It is impossible to quantitatively express all corrosion factors influencing loss of the reinforcement structural capacity. Their influences on the structural design could be considered through a factor of safety applicable to the corrosion limit state. Factor of safety is calculated considering fuzzy sets theory and qualitative inputs of various influencing factors.
This paper studies problems of hard facing of damaged and initially cracked mechanical engineering heavy parts of complex geometry such as large rams of air powered drop hammers. During long-term exploitation, these parts are subjected to thermal fatigue due to cyclic temperature changes and variable impact compression. Taking into consideration high ram costs and difficulties to purchase ram, the necessity of its reparation becomes obvious. The choices of the most suitable technologies of hard facing and welding of an initially cracked ram are also studied here. Besides the techno-economic analysis, an energetic analysis is performed as an additional criterion in assessment of the proposed technology.reparation of the biggest rams of the mass of about m UK = 6000 kg, including hard facing of initially cracked and damaged operating surfaces of the rams.Note that, following the proposed technology, two rams have been successfully repaired so far. One of them has been used since 2002 and the other since 2005, which is significantly longer than the warranty period given by the manufacturers.
Working environment for a ram of air powered drop hammerThe ram (figure 1) is exposed to impact compressive loads, and partially also to the temperature gradient, i. e. to the thermal stresses, caused by an unbalanced temperature field [1][2][3][4][5][6]. This intensively loaded mechanical part operates under very complex conditions since, during exploitation, it is exposed to mechanical and thermal loads of high intensity. After a long period of operation, i. e. after a high number of repeated cycles, cracks are observed on the ram, as shown in figure 1.
The Spectral-Analysis-of-Surface-Waves (SASW) method is a seismic technique for in situ evaluation of elastic moduli and layer thicknesses for layered systems, such as pavements and soils. The objective of the SASW test is to obtain the experimental dispersion curve and, through an inversion procedure, obtain the profile of an elastic moduli of the layered system. The inversion process in practice uses an average of dispersion curves for different receiver spacings. Results of theoretical studies indicate that differences in dispersion curves for various spacings are a result of interference of a number of body and surface waves. The development and application of neural networks to perform the inversion procedure for SASW testing of asphalt concrete (AC) pavements is presented. The most important feature of the developed network is that training of the network was done by the dispersion curves for individual receiver spacings. The training set consists of dispersion curves for seven receiver spacings and 78 dimensionless frequencies, while output is presented by elastic moduli and layer thicknesses of a four-course AC pavement. The dispersion curves used to train the neural networks are synthetic dispersion curves developed from numerical simulations of the SASW test. The obtained neural network model is compared to the previously developed model for backcalculation of moduli from the SASW test based on the averaged dispersion curve. Although both approaches can accurately define profiles, each has some advantages in evaluation of the thickness of the subbase.
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