Current Issue : October - December Volume : 2019 Issue Number : 4 Articles : 5 Articles
The durability of subsea tunnels under the coupled action of stress and chloride ions\nwas analyzed to estimate the service life and provide a theoretical foundation for durability design.\nThe influence coefficient of the stress on chloride ion transmission at lower stress levels was discussed\naccording to the material mechanics, and was verified by experimental data. A stress calculation model\nof a subsea tunnelâ??s lining section is proposed based on the plane-section assumption. Considering\nthe space-time effect of the convection velocity, a partial differential equation was constructed to\ncalculate the chloride ion transfer condition under the coupled action of stress-convection-diffusion.\nThe numerical solution of the partial differential equation was solved and the sensitivity of the\nparameters was analyzed. The subsea tunnelâ??s time-varying reliability index was calculated following\nthe Monte Carlo method, and was used to predict the service life. The results show that the chloride\nion concentration calculated by considering the coupled action is larger and the reliability index is\nlower than calculated only considering diffusion. Our findings contribute to the conclusion that\ndurability designs of subsea tunnels should consider the coupled action of stress-convection-diffusion.\nAn effective method to improve the service life of a subsea tunnel is to reduce the water-binder ratio\nor increase the thickness of protective cover....
Local scour is the removal of soil around bridge foundations under the erosive action\nof flowing water. This hydraulic risk has raised awareness of the need for developing continuous\nmonitoring techniques to estimate scour depth around bridge piers and abutments. One of the\nemerging techniques is based on monitoring the vibration frequency of either bridge piers or a\ndriven sensor in the riverbed. The sensor proposed in this study falls into the second category. Some\nunresolved issues are investigated: the effect of the geometry and material of the sensor, the effect of\nthe embedded length and the effect of soil type. To this end, extensive laboratory tests are performed\nusing rods of different materials, with various geometries and lengths. These tests are conducted\nin both dry sand and a soft clayey soil. Since the sensor will be placed in the riverbed, it is crucial\nto evaluate the effect of immersed conditions on its response. A numerical 3D finite-element model\nwas developed and compared against experimental data. This model was then used to compute\nthe â??wetâ?? frequencies of the sensor. Finally, based on both the experimental and numerical results,\nan equivalent cantilever model is proposed to correlate the variation of the frequency of the sensor to\nthe scour depth....
Prefabricated underground structures were first researched in China to address the serious social and environmental issues\nassociated with underground construction. Five metro stations have been built on Line 2 of the Changchun Metro in China\nusing this new prefabrication technology. The joints connecting prefabricated elements are the most critical components in\nsuch prefabricated structures. In this study, experiments and numerical simulations investigating the influences of different\ngrouted mortise and tenon joint geometrical parameters were conducted to determine the optimal parameters and ensure\nproper performance. To do so, a finite element model was built with the appropriate characteristics using the experimental\nresults, and an analysis of the influence of different geometrical parameters was conducted.The results indicate that\nincreasing the dip angle of the tenon could improve the flexural rigidity of the joint, but its effect was relatively small\ncompared to that of the other parameters. Increasing the width of the tenon only had a positive effect on the flexural rigidity\nof the joint when the width was relatively small and under small axial loads. Increasing the length of the tenon helped to\nenhance the flexural performance of the joint; however, this advantage was not obvious when the tenon length was relatively\nlong. Proper indentation of the joint improved the flexural capacity under a small axial load, but was not beneficial under a\nhigh axial load. The findings of this study are of value to help researchers and engineers more effectively design prefabricated\nunderground structures....
Chloride-induced corrosion is widely accepted as one of the primary causes of premature deterioration for concrete structures in\nmarine or deicing salt environment. For precast concrete (PC) structures, such durability problems may even be severer because\ndefects in joint areas, e.g., cracks caused by grout shrinkage and improper construction, can accelerate chloride ion transportation\nprocess and may cause the interface shear failure when subjected to seismic load. By applying the path probability model (PPM)\nand reliability theory, a probabilistic framework was proposed to predict three limit states of PC structures, including corrosion\ninitiation, serviceability limit state, and ultimate limit state. Using Monte Carlo simulation, a beam-to-column joint was further\nanalyzed to illustrate the differences between PC structures and those cast in situ. The analysis indicates that corrosion initiation\nand serviceability limit state are sensitive to chloride diffusivity at connection area, and the higher pitting factor can significantly\ninfluence the bearing capacities of PC structures....
This paper addresses a comprehensive design of RCC T-beam Bridge based\non AASHTO design standards. The bridge is designed and proposed to be\nconstructed over an irrigation canal (Zahirshahi canal) of Kandahar province,\nAfghanistan that has more than 30 bridges over it. Yet they are not enough,\nand the demand for construction of new bridges is gradually arising because\nof the vast urbanization in the surrounding of the canal. Most of the bridges\non this canal are Reinforced Concrete Slab (RCS) bridges; these type bridges\nare limited by capacity and are generally found only in smaller spans. Since\nthey can only span short distances and are often constructed as multiple-span\nbridges with vertical supports between the abutments to allow a longer length.\nAll constructed slab bridges over Zahirshahi canal are four-span bridges.\nConstructing multi-span bridges on the canal decreases waterway due to the\nexistence of many piers and footings that could increase the water level\nduring the peak flow, even, sometimes can cause over flow. Taking into\nconsideration these deficiencies of the present (RCS) bridges, two-span RCC\nT-beam Bridge is one of the best alternatives to be constructed over the canal.\nIn addition, canal cross-sectional dimensions are almost constant along its\nlength, though the construction of two-span RCC T-beam bridge is applicable\nat any point of the canal. The design is selected based on exclusive survey of\nthe area during all seasons including the peak flowing of the canal....
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