Investigation On Seismic Behavior Of Jointed Precast Concrete Frame Structures

Owing to a variety of advantages including: increasing productivity, improving products' quality, reducing environmental disturbance, and contributing to sustainablility etc., precast concrete has been widely applied in the world. The investigations of seismic behavior of precast concrete structures commenced in 1970s. However, studies in the jointed precast connections and structures have been much less than those in the monolithic emulation connections and structures during the past twenty years. The international cooperation program "Seismic Behavior of Precast Concrete Structures with Respect to Eurocode 8" initiated by European Community in 2003 aimed to investigate seismic behavior of the jointed precast concrete structures and to offer evidences for modification of Eurocode8. As one of the participants, Tongji University has taken in hand a series of testing and analysis works. This dissertation attempts to expand the researches of seismic behavior of the jointed precast concrete frame structures based on the program.Firstly, the cyclic tests on four plane beam-to-column connections including one cast-in-situ connection, one monolithic emulation connection and two jointed precast connections with bolts and rubber cushions were carried out. Test results of the four connections were compared. It was concluded that compared with the cast-in-situ connection the monolithic emulation one held the same strength, ductility and deformation but earlier stiffness attenuation and less energy dissipation; and the jointed precst connection possessed the features of great elastic deformation, small stiffness, ductility, energy dissipation and nonlinear elastic hysteretic characteristic. According to the test results, restoring moment-rotation relationship of jointed precst connection with bolts and rubber cushions was put forward.Next, the pseudodynamic tests of three jointed precast concrete frame structures including two frames with one floor and double spans, one frame with one floor, single span, and two bays were carried out. Test results indicated that the failure mechanism of the structures was ductile with column bending failure, and the displacement ductility factor was larger than 3.5; when drift angle arrived at 1/25 the structures still held enough carrying capacity; the beam-to-columns connections worked well without visible damage; the floor slab-to-beam connections being destroyed at first may be attributive to the weakness of this sort of structures. It is suggested to strengthen the roof slab-to-beam connections or to employ flexible ones. Test results revealed that the jointed precast frame structure could provide a satisfactory seismic performance.Resorting to Strand7 software numerical simulations of jointed precast connections and structures were carried out. By employing the entity element model and considering the superelasticity of rubber, the contact interfaces between rubber cushion and beam or column and the prestressing of bolt, the restoring moment-rotation relationships of the jointed connections were educed through numerical calculation. It is the basis of numerical simulation of the whole jointed precast structures.By applying the component element model and considering the nonlinear restoring moment-curverture relationships of beams and columns which were calculated by USC_RC softwear and the nonlinear restoring moment-rotation relationships of jointed precast connections which were calculated by the connection numerical simulation above, the nonlinear transient dynamic analysis of the jointed precast structures of the pseudodynamic tests was conducted. Through comparing the results of the numerical simulations and the pseudodynamic tests, the calculation method and model were proved reliable and the calculation parameter was revised.Through numerical simulation method the influence of jointed connection in seismic response of precast frame structures was investigated, and the concept of sensitivity region of joint stiffness was put forward. When joint stiffness was outside of sensitivity region, the jointed connection can be regarded as hinge or fixed joint, otherwise the stiffness of connection should be considered specially.Eurocode8 was introduced and some provisions were compared with the Chinese code of the seismic design. A real design example was presented to illustrate the differences of the two codes. The behavior factor regarded as the most important design parameter in Eurocode8 and differing from the Chinese code of seismic design should be fixed on carefully. According to the results of test and numerical simulation, behavior factors of the test structures were calculated and the reasonable value of behavior factor of the jointed precast concrete frame structure was suggested.Finally, the seismic behavior of jointed precast concrete frame structures was summarized and the key problems requiring further studies were discussed.