Seismic Performance And Design Method Of Storey-Adding Out-Jacketing Prestressed Concrete Frame Cooperated With Existing Structure

Using out-jacketing structure for storey-adding has become one of the most concerned topics in the circles of civil engineering. For taller existing structures, it is appropriate to combine out-jacketing frame column with the existing structure at each frame joint, which makes the tow structures cooperated. Thus the column size of out-jacketing frame can be reduced; also the weakness of lateral stiffness of out-jacketing frame can be relieved. Based on the seismic requirement"no damage in frequent earthquake and no collapsing in rear earthquake", five aspects of research work are carried out as following:(1) Using APDL, program for internal force and reinforcement calculating of prestressed concrete out-jacketing frame is compiled. Analysis is carried out on performance of the out-jacketing frame under frequent earthquake. Analysis shows that internal force of the existing structure changes after storey-adding: moment and shear force of column and beam upside of the existing structure increase obviously, while moment and the shear force underside decrease. Combination to out-jacketing frame column makes the existing structure change its working state from pure frame structure to be like frame shear wall structure, in which the column of out-jacketing frame is just like the shear wall: it carrys most lateral force underside of the existing structure and increases the lateral force upside of the existing structure.(2) Analysis on seismic performance and plastic hinges mechanism of prestressed concrete out-jacketing frame is carried out. It is suggested that the positive plastic hinges can be set at beam where its position is 0.1 times of the span to the end of the beam. Thus supper-bending of the beam can be decreased visibly. Prestressed concrete frame beams designed with span-plastic hinge are tested under low cyclic loadings. The result provides reference to the out-jacketing frame seismic analysis. Experiment shows that cracks of span-plastic hinge appear more concentrative and wider than the one of end-plastic hinge, and the length of span-plastic hinge is shorter than the one of end-plastic hinge. Energy dissipation capacity and displacement ductility of span-plastic hinge is a little worse than those of end-plastic hinge. Numerical simulation analysis shows that the length of plastic hinges at beam span in practical structure is quite longer than the one in specimens, ductility in practical structure is also better than the one in specimens. It is safe and feasible that the tensile non-prestressed steel bar in the plastic hinge is conformed to the regulation of minimum reinforcement ratio of reinforcement at bottom of concrete frame beam in Concrete structure design code (GB50010-2002).(3) By IDARC, elastic-plastic time-history analysis on the out-jacketing frame designed by Concrete structure design code (GB50010-2002) is carried out. Analysis shows that lateral stiffness of the frame is weak at the underside of the frame , which is likely to cause the whole structure collapse. Some frames collapse under strong earthquake. The number of collapsed frame and destroy degree of the frame all increase when earthquake intensity increases or ground cycle increases. Calculation shows that span-plastic hinge can reduce the burden of the out-jacketing frame column. It is suggested that out-jacketing frame cooperated with the existing structure can be built at soil siteâ… ,â…¡,â…¢in zone of intensity 6 & 7, soil siteâ… ,â…¡in zone of intensity 8; seismic level of the frame can be set as Third in zone of intensity 6, Second in zone of intensity 7 and First in zone of intensity 8; axial compression ratio limits of the out-jacketing frame column of each seismic level should be lower 0.1 than the one in Concrete structure design code (GB50010-2002); the end-column moment magnification factors should be increased moderately. Strengthen constructions are also bring forward to intensify the seismic performance of the frame. Calculation shows that no out-jacketing frame collapses in strong earthquake by by using these strengthen methods.(4) Analysis on reasonable mechanical model, design method and checking force selection, construction and anchor of the connect component are carried out. Reasonable mechanical model of the connect component is suggested. For the safe working of connect component whenever the building subjected to gravity load, frequent earthquake or strong earthquake, the standard value of connect component axial force resistance should no less than (2.0~2.5) times of the design value of connect component axial force under frequent earthquake. A type of construction for connect component is also presented.(5) 8 aspects of design suggestions on prestressed concrete out-jacketing frame for storey-adding cooperated with the existing structure are presented, in which general principles, general requirements, types of structure, choice of materials, design rules of the frame beam, column and connect component are all included. It can be served as reference to the research and design of the out-jacketing frame for storey-adding cooperated with the existing structure.