| The precast segments cementing assembling technology has been widely used in bridge field at home and abroad,but the related theoretical research mainly focuses on static shear and bending mechanical properties.There are still some uncertainties about the crack development mode,the working state of the epoxy joints and the fatigue failure mode of this kind of structure under cyclic loading.The fatigue properties of precast segmental structures with epoxy joints are studied experimentally.The main contents and conclusions are as follows:(1)Three precast segmental beams with epoxy joints were designed and manufactured.And the internal prestressing were tensioned for text beams.Two Static load tests and one fatigue test were carried out.And the properties of PSB785 Scres-thread steel bars were also tested.The test results show that shear-compression failure occurs in static test and bending failure caused by fatigue fracture of prestressing tendon occurs in fatigue test.The location and sequence of cracks are almost the same,and the epoxy joints and the bond between the joints and the concrete have not been destroyed,which shows a good integrity and fatigue performance.(2)The natural frequency,variation rules of mid-span concrete strain,oblique section strain,top concrete pressure strain in mid span,deflection and maximum crack width with the number of cycles are analyzed under cyclic loading.And the development laws of residual strain and residual deformation are studied.It is found that the parameters have obvious changes in the initial stage of cyclic loading and change steadily in the process.(3)The periodic creep of concrete is calculated,and the fatigue strength checking of materials are carried out.The revision suggestions of theoretical formula suitable for precast segmental assembling beam are given.(4)The ABAQUS finite element model of the test beam is established and verified.The loading process of the fatigue test beam is simulated by using the simplified calculation method of the whole fatigue damage process.The main calculation results of load-deflection relation,the principal tensile stress,principal plastic strain and the strain of steel bars and concrete are analyzed,which are in good agreement with the test results.(5)The effects of bonding defects and prestressing level on fatigue properties of test beams are studied by numerical model.At the same number of cycles,the bonding defects of the joints cause the attenuation of the fatigue performence to varying degrees.Increasing the prestress level moderately will help to avoid the development and extension of fatigue cracks.(6)Based on the experimental and finite element analysis results,some suggestions for the design and construction of precast segmental assembling structures are put forward. |
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