Study On Base Isolation Technology Of Steel Frame-Braced Structure With Large Aspect Ratio

Base isolation technology can effectively improve the seismic resistance and seismic safety reserve of structures,and is gradually applied to high-rise and super high-rise buildings.With the increase of building height-to-width ratio,the risk of overturning and collapse of base isolated structure increases,and the isolation efficiency decreases gradually,which becomes the main problem in the breakthrough and application of base isolation technology of large aspect ratio structure.The light weight and high strength of the steel structure and the large lateral stiffness of the braced frame system are beneficial to improve the seismic isolation efficiency and restrain the dynamic overturning effect of the structure.In this paper,according to the lateral deformation characteristics of the steel frame bracing system and the horizontal swing effect of the isolation layer,the nonlinear dynamic differential equation of the multi-particle system is established and the computer program is compiled.The Newmark-β step-by-step integration method and Newtown-Raphson stiffness iterative method are used to solve the seismic time-history response of the structure.This paper discusses the influence of structural characteristics such as height-towidth ratio and stiffness-to-weight ratio on the design control parameters such as bottom shear ratio,inter-story displacement angle,vertical tensile stress of support,horizontal displacement of isolation layer and anti-overturning moment ratio of structure after and before isolation,so as to clarify the limit value of height-to-width ratio for high-rise isolated structures to meet the requirements of overall stability and anti-overturning performance.The range of the optimal stiffness-weight ratio is proposed,which can not only achieve the expected isolation effect,but also effectively restrain the overturning effect of the structure.The buckling restrained brace with stable tension-compression performance and ideal energy dissipation capacity is used as the main lateral force resistant member of the base isolation steel frame bracing system with large aspect ratio.By increasing the area of the bracing core material,the rigid-weight ratio of the structure is improved to obtain more ideal seismic isolation efficiency and achieve the goal of multi-level seismic fortification.Combined with the anti-seismic conceptual design idea of multi-line of defense,the braces can not be strengthened without limit,and the frame can not be weakened without limit.The matching problem of buckling restrained brace and the lateral stiffness of steel frame in the upper isolation layer is studied.The reasonable selection range of lateral stiffness ratio of braces and frames is proposed,and a practical design method of buckling restrained brace in base isolation buildings is proposed.Aiming at the super high-rise steel frame braced structure with large aspect ratio in a high intensity area,the combined control technology of buckling restrained brace and base isolation is adopted to design the structure,and a three-dimensional finite element solid model is established and elastoplastic dynamic time-history analysis is carried out.the seismic performance and seismic safety reserve of the structure are studied in order to provide reference for the combined design of seismic reduction and isolation of buildings with large aspect ratio.The results show that:1.Increasing the stiffness-weight ratio of the superstructure is not only beneficial to improve the overall stability of the structure,but also conducive to the improvement of seismic isolation efficiency and the realization of multi-level fortification goal,but the anti-overturning ability of the structure is reduced.According to the reverse control effect of structural stiffnessweight ratio on seismic isolation efficiency and anti-overturning performance,the target value of stiffness-weight ratio in the best equilibrium state is found.It is obtained that the structures with different aspect ratios meet the stability requirements and can achieve the minimum stiffnessweight ratio of the expected seismic isolation design objectives(taking the bottom shear ratio and the inter-story displacement angle as the index)and the anti-overturning performance requirements(taking the horizontal displacement of the isolation layer,the support tensile stress and the structural anti-overturning moment ratio as the index).The maximum stiffness-weight ratio of the structure,and puts forward the limit value of the height-to-width ratio to meet the requirements of the overall stability under the optimal suppression of the overturning effect of the structure.The purpose of this paper is to provide reference for the breakthrough and application of structural base isolation technology with large aspect ratio in high intensity area.2.For the steel frame braced base isolation structure with higher height and larger aspect ratio,the buckling restrained brace with more stable tension-compression performance and better energy dissipation capacity is used to replace the ordinary steel brace.the yield condition of the buckling restrained brace prior to the upper steel frame of the base isolation is easy to be satisfied.The maximum inter-story displacement angle of buckling restrained brace-steel frame base isolation system under earthquake decreases with the increase of the ratio of bracing to frame lateral stiffness,and the decreasing rate gradually slows down and finally tends to a fixed value.This paper explores the critical design value of interstory displacement angle of base isolated steel frame,and puts forward a method of buckling restrained brace design based on the target displacement of isolated structure,that is,the preliminary design of base isolated steel frame system is carried out according to the requirement of structural bearing capacity.the intermediate story displacement response is calculated and compared with the critical design value,and then the bracing-frame lateral stiffness ratio is determined and the buckling restrained brace is designed.Finally,the seismic performance of buckling restrained brace-steel frame base isolated structure under rare and rare earthquake is checked.The numerical example shows that the buckling restrained brace-steel frame base isolation structure designed according to the critical value of inter-story displacement angle of moderate earthquake is easy to meet the threelevel fortification requirement of "unbreakable in moderate earthquake,repairable in large earthquake and non-collapse in giant earthquake".3.Aiming at a super high-rise steel frame bracing system with large aspect ratio in high intensity area(building height 160.2m,aspect ratio 4.1),the original structure is jointly controlled by base isolation and energy dissipation of buckling restrained brace.By adjusting the structural rigid-weight ratio and bracing-frame lateral stiffness ratio,the ideal seismic isolation efficiency can be obtained and the seismic fortification goal can be achieved.Under strong earthquake,seismic isolation bearing and buckling restrained brace play the role of energy dissipation at the same time,which can not only give full play to their advantages,but also make up for the deficiency when used alone.The combined system of shock absorption and isolation has a larger safety reserve in resisting the possible super-rare intensity earthquake,and the effect of vibration control tends to be significant with the increase of ground motion intensity.The above analysis methods and research conclusions can provide reference and basis for theoretical research and practical engineering application of large aspect ratio steel frame-braced structure base isolation technology.