Research On Performance-based Seismic Design Method Of Low Yield Point Concentrically Braced Frames

Concentrically braced steel frame structure is an effective lateral brace system,The design concept of the system is to strengthen the brace so that the structure can bear greater seismic force to support the "hard" earthquake.In this traditional strong brace system,The bracing is easily buckled after repeated tension and the seismic force is transferred to the frame after buckling,which leads to a large extent of damage for the frame.Therefore,a low yield strength(usually around 100MPa)and relatively stable,smaller flexion,good resistance to low cycle fatigue,large elongation and the very low-yield-point steel braces with strong plastic deformation have come into being.It weakens the brace in the frame supporting structure system,and changes the seismic mechanism of strong support to the energy dissipation mechanism of weak support,which has broad engineering application value.With the development of the seismic design theory and the requirements of the reliability of the building becoming increasingly strict,the research on performance-based seismic design method for low yield point concentrically braced steel frame structure is the key to popularize and use this effective lateral force resisting system.According to the low-yield-point concentrically braced structure system,the performance-based seismic design method of the low-yield-point concentrically braced steel frame structure is systematically improved for the establishment,quantification,verification and analysis of the performance objectives and how to achieve in this paper.The main research contents are as follows:(1)A low yield point concentrically braced steel frame performance standards and design criteria were establishesd for the low-yield-point steel braced frame structure stress and deformation characteristics,the division standard of reference to domestic and foreign research results and performance standards,and in accordance with our building aseismic design criterion related performance design requirements.(2)Combined with the requirements of domestic and foreign tests,finite element data and the code for seismic design of buildings in China,the performance level and reference index of low yield point center support structure are proposed.and And quantifying the proposed targets.Finally,The specific quantitative indicators of the structure.is obtained.(3)In order to realize all the indexes quantified in this paper,using displacement-based seismic design principles,seismic design methods are given in terms of equivalent single-degree-of-freedom systems,displacement response spectra,and target displacement,from basic assumptions,loading patterns,Performance points,plastic hinges,and implementation steps give specific evaluations of their seismic design.(4)3 groups of unidirectional tensile tests were conducted for low-yield-point(LYP100)steel,and the constitutive relations and main mechanical properties of materials were obtained,which lay the foundation for theoretical analysis and data models in this paper.(5)According to the displacement index and displacement-based seismic design principles mentioned above,the design process of the 10-story low-yield-point center-supported steel frame structure under four different performance levels is presented in detail,The demand curve and pushover curve of the structural system are obtained,and the performance of the structure is evaluated by the capability spectrum method.Under the performance goal 1,the structural performance level requirement is the highest,and the structure is in the elastic state under three different earthquake levels;Under performance objective 2,the performance level requirement is slightly lower than performance 1,and the support only yields energy under large earthquakes;Under performance target 3,the support began to yield under medium and large earthquakes,participating in the energy consumption of the structure,and the outer frame remained intact;Under performance objective 4,the structural performance level requirement is the lowest.Under the action of moderate earthquakes,only the supports participate in energy dissipation.Under the action of large earthquakes,individual frame beams also begin to yield as the seismic level increases,and the overall structure meets the performance design.It is required to exert the characteristics of the yield energy of the center-supported steel frame structure with a low yield point and have good seismic performance.