Research On Aseismatic Behaviour Of Unbonded Prestressed Concrete Flat Beam Frame Joints

AbstractWith the development of economy and society, high buildings and wide-span structures, which structural types are tending to be diversified, come forth continuously. Unbonded prestressed concrete flat beam floor is widely applied in the structures above mentioned. As a new structural system, the width of flat beam section is not only larger than its height, but also larger than the width of column section, which makes the mechanism of loads transfer in the joints more complex. Less systematic researches in the behaviour of loads transfer, design methods and construction measure are processed at home and abroad. And there aren't specific regulations for unbonded prestressed concrete flat beam frame joints in the Chinese aseismatic design specifications. In order to make the structural system more popularized, especially in the zone of seismic defense, it's necessary to research the aseismatic behaviour of these joints.Based on the theory and test, the aseismatic behaviour of the joints in the middle level of unbonded prestressed concrete flat beam frame is analyzed and discussed in this paper. Varied-angle truss model is applied to analyze the loading behaviour of the exterior core of unbonded prestressed concrete flat beam frame joints under the torsion plus shear, bend and compression. And a new formula is derivated to reflect the inflection of additional torsion to the exterior core of the joints. The aseismatic behaviour of the joints is surveyed by means of pseudo-static test, which takes into account the different affection of the unbonded prestressed tendons respectively passing through the interior core and the exterior core with the same PPR. And the aseismatic capacity of shear resistant strength, deform, energy dissipation, ductility and rigidity degeneration is also researched.The major conclusions from the model of failure and data analysis are shown in the following item:1.The failure model of + is shear failure in the exterior core, while that of is bend and shear failure in the ends of flat beam.2.In the process of pseudo-static test, the stress of unbonded prestressed tendons is invariable approximately before the yielding of the specimens. The tendons don't begin to take action until the specimens yield, but don't yield themselves in the whole process.3.The displacemental ductility coefficients of the joints in the middle level of unbonded prestressed concrete flat beam frame surpass 4, which means this type of structure has better ductility and can meet the demands of ductility aseismatic design.