دانلود رایگان مقاله انگلیسی الگوریتم عددی فرآیند پوشش ترک خوردگی برای تونل های فشار - امرالد 2017

Abstract

Purpose – The cracking of a reinforced concrete lining has a significant influence on the safety and leakage of pressure tunnels. This study aims to develop, validate and apply a numerical algorithm to simulate the lining cracking process during the water-filling period of pressure tunnels. Design/methodology/approach – Cracks are preset in all lining elements, and the Mohr
Coulomb criterion with a tension cutoff is used in determining whether a preset crack becomes a real crack. The effects of several important factors such as the water pressure on crack surfaces (WPCS) and the heterogeneity of the lining tensile strength are also considered simultaneously. Findings – The crack number and width increase gradually with the increase in internal water pressure. However, when the pressure reaches a threshold value, the increase in crack width becomes ambiguous. After the lining cracks, the lining displacement distribution is discontinuous and steel bar stress is not uniform. The measured stress of the steel bar is greatly determined by the position of the stress gauge. The WPCS has a significant influence on the lining cracking mechanism and should not be neglected. Originality/value – A reliable algorithm for simulating the lining cracking process is presented by which the crack number and width can be determined directly. The numerical results provide an insight into the development law of lining cracks and show that the WPCS significantly affects the cracking mechanism.

6. Conclusions

This study, while aiming to provide a direct solution of the number and width of the lining cracks, presents a numerical algorithm to simulate the cracking process of reinforced concrete lining for pressure tunnels. In contrast with the previous research, the discrete crack model is applied. The number and width of the lining cracks can be directly solved, by simultaneously considering the effect of several important factors, such as the WPCS and the heterogeneity of the lining tensile strength. The present algorithm can better capture the mechanical properties of the pressure tunnel and help provide a better insight into its working mechanism.

The numerical results show that with the increase in water pressure, the lining cracks appear progressively and the crack width gradually increases. However, when the water head reaches a certain value, the increase in crack width is not evident, while the crack number increases further. After the lining cracks, the lining displacement distribution is discontinuous and the steel bar stresses are not uniform. The steel bar stress near a crack is much greater than that in the intact concrete, due to which the steel bar stress is not uniform and the measured value is to a great extent determined by the position of the stress gauge. Moreover, the WPCS has a significant influence on the lining cracking mechanism and should not be neglected. When the WPCS is considered, the final crack number reduces considerably and the crack width evidently increases.