Study On Seismic Behaviour Of Hybrid Fibre Reinforced Shear Keys And Immersed Tunnel

In recent years,more and more transportation system underseas were constructed except the traditional transportation.A large scale of immersed tunnels with complex construction technology,difficult design and high scientific content were constructed,the most typical immersed tunnel among those was the immersed tunnel that connected Hong Kong-Zhuhai-Macao.Meanwhile,China located between the Eurasia seismic belt and the circum-pacific seismic belt.Therefore,the structures and buildings in most areas of China need to be designed with earthquake resistance protections.Thus,the security problems of the immersed tunnel under seismic loads are becoming more and more important.The seismic behaviour of concrete shear keys in the immersed tunnel joints that resist the seismic loading need to be focused on.This study develops a new type of hybrid fibre reinforced concrete(HFRC)material.The seismic behaviour of hybrid fibre reinforced concrete shear keys and immersed tunnel was systematically studied.The primarily works and conclusions were summarized as follows:(1)Based on the material tests of hybrid fibres reinforced concrete,the mechanical properties including uniaxial compression,uniaxial tension,flexure and shear of plain concrete,steel-basalt-polypropylene HFRC,steel-basalt HFRC and steel-polypropylene HFRC were studied.The compression strength of cubic,the uniaxial compression strength of prism,the uniaxial tensile strength,splitting tensile strength,shear strength and flexure strength were obtained from the material tests.Besides,the stress-strain curves of uniaxial compression and uniaxial tension,the load-displacement curves under four points flexure and direct shear were obtained from the tests.Through the parametric analysis of the HFRC under compression,tension,direct shear and flexure,the specific composites of HFRC with the highest strength,best toughness and optimal mechanical properties were obtained.Comparing the strength and toughness of HFRC with plain concrete,the uniaxial compress strength and toughness were improved 8.5%~16.5%and 18%~24%,respectively;the uniaxial tensile strength and toughness were improved 64.1%~87.4%and 108.3%~200%,respectively;the shear strength and toughness were improved 70.9%~116.4%and 791.2%~1041.2%,respectively;the flexure strength and toughness were improved 13.6%~42.2%and314.3%~551.4%,respectively.(2)Based on the optimized composites of HFRC,the seismic behaviour of normal concrete shear keys and HFRC shear keys under cyclic loading were tested.The seismic behaviour indexes that consisted of failure process,failure characteristics,carrying capacity,hysteretic characteristics,deformation behaviour,energy dissipation capacity,damage evolution,stiffness degradation,cracks spreading on the concrete surface,the strain of the concrete and the strain of steel bar were analyzed.Meanwhile,the contributions of different concrete grades,different reinforcement ratios and different volume fractions of fibres to the seismic behaviour of shear keys were revealed.Adding180 kg/m~3 steel fibres and 4.5 kg/m~3 basalt fibre to HFRC improved the ultimate load-carrying capacity,energy dissipation ability,and ductility of shear keys by 44.6%,229%,and 53.1%,respectively.(3)The finite element software ABAQUS was adopted to simulate the tests.The strain-damage relationship of steel-basalt HFRC was established according to the uniaxial compression and uniaxial tension stress-strain curves.Subsequently,the direct shear test of material tests was simulated by ABAQUS.Based on the simulation of direct shear test,the seismic behaviour tests of concrete shear keys were simulated and analyzed by ABAQUS.The relationships of uniaxial compressive enhancement factor versus volume fraction of fibres and uniaxial tensile enhancement factor versus volume fraction of fibres were regressed based on the results of material tests for the shear keys.Meanwhile,the formula to calculate the ultimate shear resistance of the shear keys was regressed based on the hysteretic tests results of the concrete shear keys.The maximum error and the minimum error of the formula to calculate the ultimate shear resistance were 13%and 1%,respectively.(4)A three-dimensional finite element model of the soil-immersed tunnel structure was established in ABAQUS,and the viscoelastic artificial boundary was adopted to simulate the actual soil boundary.Besides,the oblique incidence of the seismic loading was realized by the equivalent nodes stress time-history method.The seismic behaviour of the immersed tunnel joint between segments with steel-basalt hybrid fibre reinforced concrete were compared with the immersed tunnel with normal concrete.The difference between the seismic response of immersed tunnel with hybrid fibre joints and immersed tunnel with normal concrete were studied through the analysis of the deformation for the immersed tunnel,the damage of the segment element,the variation laws of the deformation for the roof-floor plate of the immersed tunnel and the behaviour of the shear keys in the immersed tunnel joints.Comparing the simulation results of HFRC immersed tunnel joints with plain concrete immersed tunnel joints,the deformation of the whole structure decreased 25%~30%,the deformation of the joints decreased20%~30%,the deformation of the shear keys decreased 30%~40%.