| Security of critical conveyance structures,such as long-distance water conveyance tunnels and large-scale aqueduct structures is vital to the normal operation of South-to-North Water Transfer project.Structural design and material selection are so important that the requirements of crack resistance and earthquake protection should be satisfied from these two aspects,to reduce or even eliminate maintenance and repair expense,and guarantee the safe operation of foundational establishment.On the basis of ultra high toughness cementitious composite(UHTCC),a new kind of green structural material,exploratory research work on new material structures is carried out in the present research,to establish calculation theory of reinforced UHTCC flexural members and propose an aseismatic,crack-reesistant and durable new material composite structures.And this research is part of the Key Program of the National Natural Science Foundation of China(No.50438010) and the Research and Application Programs of Key Technologies for Major Constructions in the South-North Water Transfer Project Construction in China(JGZXJJ2006-13).In orter to perform the aim mentioned above,the details are as follows:1.Combining both advantages of carbon textile and UHTCC,research on thin UHTCC components reinforced with carbon textile(CTRUHTCC) is carried out.It takes a fire-new choice of structural materials for crack-resistance of large-span shell structures in hydraulic engineering and can be used in maintenance and strengthening of reinforced concrete structures under exposed environment.Compared with textile reinforced mortar,influences of the surface treatment of carbon textile,water-binder ratio,volume content of polyvinyl alcohol(PVA) fiber on crack resistance,load bearing capacity and bond property of the tested composite have been investigated through four-point bending experiments and pull-out tests. Eleven series of specimens are used for the both experiments.The specimen dimensions are 400 mm×100 mm×10 mm for four-point bending test,and 140mm×60mm×10mm for pull-out test.The proposed approach for surface treatment of carbon textile by spreading sands on the surface of carbon roving impregnated with an epoxy resin is found to be a practical method that obviously improves bond properties between textile and UHTCC matrix. 2.By making use of prominent non-linear deformation capacity,excellent mechanical performances,compatible deformation ability with steel reinforcement and outstanding crack-resistance of UHTCC,investigations on flexural behavior of reinforced UHTCC (RUHTCC) long flexural members are carried out.Based on mechanical constitutive models of materials and plane section assumption,theoretical calculation model of RUHTCC flexural members is established and detailed analysis on development of internal forces during the whole bending process is also presented.Moreover,determination of moment-curvature relation and theoretical formulae of deflection and curvature are given in the present research.3.Three series of RUHTCC long beams without web reinforcement are tested through a four-point bending experiment to verify theoretical formulae of RUHTCC flexural members proposed in the present research.It is discovered that for RUHTCC beams,plane-section assumption is tenable.Totally,there are twelve RUHTCC beams with three different reinforcement ratios and three ordinary reinforced concrete beams as reference specimens in the test,and the dimensions of them are 2450 mm×120 mm×80 mm.Compared with reference specimens,yielding of reinforcement can be delayed in RUHTCC beams,and the failure pattern of RUHTCC specimens represents a ductile response,ensuring the safety and reliability of structures in seismic protection.UHTCC can continue undertaking tension load after cracking due to the strain-hardening feature,therefore,load bearing capacity and ductility of structures or components can be improved and steel products can be saved. Electric resistance strain gauges and a crack width measurement instrument with a 40×lens are used to monitor the propagation of crack and development of crack width.It is found that crack width in RUHTCC beams is limited to 0.05mm under service load conditions and can be considered without negative influence on durability.4.Simplified calculation method of RUHTCC flexural member is proposed for convenience.The critical reinforcement ratio,the minimum reinforcement ratio,deflection and curvature ductility index are also deduced.It is found that there is no need to limit the minimum reinforcement ratio when the tension strain capacity of UHTCC is high enough. Influence factors of flexural capacity and ductility,including geometric dimensions,material parameters and reinforcement ratio,have been investigated in the present research on the basis of theoretical equations.5.Investigations on bending behavior of functionally-graded composite beam crack controlled by UHTCC(UHTCC-FGC) are carried out to improve durability of reinforced concrete structures.Based on the concept of functionally graded concrete,UHTCC with excellent crack-controlling ability is strategically substituted for part of the concrete,which surrounds the main longitudinal reinforcement in a reinforced concrete member.The thesis discusses the development of internal force and crack propagation during loading process,and presents analysis of moment-curvature relationship from loading to damage and calculation of mid-span deflection and ductility index.6.Theoretical formulae are validated through experimental results of sixteen UHTCC-FGC beams with four different thicknesses of UHTCC layer.The dimensions of specimens are 2450 mm×120 mm×80 mm.Moment-curvature relation and crack pattern of UHTCC-FGC beams are discussed in comparison with three ordinary reinforced concrete beams.In addition to improving bearing capacity,the results indicate that UHTCC-FGC beams have been found to be very effective in preventing corrosion-induced damage,At last, the optimal thickness of UHTCC layer in UHTCC-FGC beams has been confirmed through stress superposition and in consideration of durability.
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