Research On Performance-based Joint Design Method For Assembled Monolithic Frame Structures

Bearing capacity-based seismic design is a theory with life safety as a single objective,which is unable to keep pace with the development of design requirements.The performance-based seismic design method(PBSD method)represents the research direction of structural seismic design in the future.But at present,the PBSD methods is mostly used in cast-in-place reinforced concrete frame joints,seldom used in assembled monolithic concrete frame joints.With the development of construction industrialization in our country,assembled buildings will be developing rapidly.In this background,a study on the PBSD method of assembled monolithic concrete frame joints is proposed in this paper.The main contents are as follows:(1)Four specimens of precast pre-stressed beam-column joints are designed,including two middle joints and two edge joints,referring to the "Scope system".Two middle joints are designed according to the height limits of compression zones of different aseismic grades,respectively,and the fiber reinforced concrete is used in post-pouring zone.Axial compression test of the concrete samples with fibers in different dosages was carried out.According to the test results,PVA fibers were selected with the dosage of 0.5%.(2)Four specimens of beam-to-column joints were tested under low cyclic reversed loading.The hysteretic curve,skeleton curve,strength-yield ratio and ductility,strength degradation,stiffness degradation and energy dissipation capacity of the specimens were analyzed.(3)After the necessary introduction of energy-based seismic design method,a theoretical research on the interlayer distribution of hysteretic energy dissipation is proposed.According to the deformation coordination principle of frame structure,the influence of plastic hinge length and beam span on the interlayer distribution of hysteretic energy dissipation of concrete frame structure is obtained.It is concluded that increasing the length of plastic hinge can reduce the proportion of plastic hinge deformation in the single span of the beam,and increase the span of the beam can reduce the proportion of plastic hinge deformation in the floor.(4)Based on the experimental data collected,the recommended value of lateral displacement requirement and the theoretical formula for calculating yield load of beam column joints under horizontal force are given.The ultimate displacement formula of beam column joint under horizontal force is established.The influence of longitudinal bar slip is considered by statistical method.Based on the proposed ultimate displacement formula and the collected experimental data,the recommended value of damage index of "slight damage" and "medium damage" for the joints of assembled monolithic concrete frame are given.(5)After a brief introduction to the current seismic design methods of reinforced concrete frame joints,according to the research on the interlayer distribution of hysteretic energy dissipation and the application of PBSD methods in assembled monolithic concrete frame joints,a damage-based function-oriented design method of assembled monolithic concrete frame joints is proposed.The research shows that the ultimate failure of the four specimens designed in this paper occurs in the post-pouring area of the beam,which meets the requirements of the code.the proposed formula for interlayer distribution of hysteretic energy dissipation is in coincidence with the distribution of hysteretic energy obtained by Modal Pushover Analysis method.Therefore,the proposed function-oriented design method is practicable.