Research On The New-Style Joints Of Precast Concrete Frame Structure

As an industrial construction method, precast reinforced concrete frame structure is popularized by designers and investors by its merits of quicker construction, better economic and environmental effects day by day. At present, the application of precast concrete frames is limited in the seismic region for that its unreliable connections can't satisfy the bearing ability of cyclic loading. Otherwise, the theories of high seismic dry-connections in precast concrete frames are lagged. For above mentioned, the performances of the dry-connections for new-type precast concrete frames are analyzed with theory and with finite-element method (FEM) based on some test data.By the performance analyses of the various dry-connections applied in precast concrete frames projects, merits and the shortages of these connections are summarized, and some of them are improved and some new ones are put forward.The main design principles for dry-connection in new precast concrete frames is to adopt corbel with higher bearing as the vertical bearing members and to adopt the steel plate with good ductibility as horizontal bearing members, and consequently to achieve the transformation of the shearing force and the bending. Furthermore, the good seismic performance could be better achieved by the rational designed steel plate. With FEM analyses four new type of joints are analysed. It is approved in the results that the bearing performances of the new dry joints parallel to or excel to the cast-in-suit one. And some vital parts of the new dry joints are found with porpose to further analyse below.The hidden corbels, the dapped-end-beams and the beam corbels applied in the new type dry-connections are analyzed with strut-and- tie model and shear-friction theory, and corresponding design formula are deduced. With the analyses of the concrete local bearing capacity, it is found that the effect of concrete initial stresses is not considered in the local bearing design methods used in the projects. The design equations considered concrete initial stresses in the column is proposed. From the discussion on embedded steel piece applied in the new connections and the seismic design of the whole connections, it is gained that the seismic performances of the whole joint could be achieved by designing rationally.By the analyses of the hidden corbels with finite element software ANSYS, the design methods put forward in the paper is validated. Based on the FEM analyses of the beam corbels and the dapped-end beams, it is found that the corresponding design equations proposed in the paper is is compared well with the results obtained from FEM analyses and that of the test data. By the FEM analyses and the contrast analyses on several local bearing design method in steel corbel connection used in projects, it can be concluded that the design equations considering the initial stress in concrete deduced in the paper could accurately calculate the local bearing with some safe storage.Finally, design proposes to the new dry connections are addressed according to the analyses above.