Study On Bearing Behavior Of Functionaily Graded Concrete Shaft Lining

Concrete thick-walled hollow cylinders are widely used in hydropower, traffic, mining and military engineering. Shaft lining is a kind of concrete thick-walled hollow cylinder. In the thick-walled cylinder design, problems such as the stress, deformation, ultimate bearing capacity, are often encountered. In order to increase the ultimate bearing capactiy of thick-walled hollow cylinder, the concept of Functionally Graded (FM), which has been widely used in some fields, i.e. Aerospace, nuclear reactors and chemical industry, was introduced into concrete material. By theoretical analysis, preparation of functionally graded concrete and physical simulation test, the application of functionally graded concept in increasing the ultimate bearing capacity of shaft lining was analyzed.(1) Based on the inversion analysis, we found that functional gradient materials (FGM) can reduce stress concentration of thick-walled cylinder and let the FGM thick-walled hollow cylinder have a higher ultimate bearing capacity than the conventional homogeneous thick-walled hollow cylinder does. As the thickness of cylinder is relatively thick, the elastic ultimate bearing capacity of FGM hollow cylinder can be improved significantly with the increase of thickness.(2) The optimal design method for doubled layered thick-walled hollow cylinder with different elastic modulus was established. The minimum wall thickness required, the best thickness ratio and the modulus ratio of inner layer to outer layer are calculated for cases in which the external load and uniaxial compressive strength are known already.(3) Elasto-plastic analysis for double layered thick-walled hollow cylinder was carried out. The effects of the axial load on the elastic and plastic ultimate bearing capacity were analyzed. As the intermediate principal stress was taken into consideration, the elastic and plastic ultimate bearing capacity of double layered thick-walled hollow cylinder increase.(4) Ratio tests were carried out in order to get the variations of the compressive strength and elastic modulus versus a number of factors. The optimal experimental factors for functionally graded concrete has been preliminarily obtained. (5) Model tests of thick-walled hollow cylinder were carried out. The tests results validated the theoretical conclusion, i.e. FGM thick-walled hollow cylinder has higher ultimate bearing capacity than homogeneous thick-walled hollow cylinder does.(6) A vertical shaft lining remotely loaded by non-axisymmetrical in situ stresses was analyzed. Two extreme boundary conditions along the liner/ground interfaces, namely, pure bond and pure slip cases, are implemented. The accurate solutions of the loads acting on the outer boundary of liner were obtained.