Study On Seismic Performance And Design Method Of Resilient Eccentrically Braced Frames

Eccentrically braced frames(EBFs) combine the excellent ductility of moment resisting frames(MRFs) with high stiffness of concentrically braced frames(CBFs).Through plastic deformation and energy dissipation of the link, the seismic response of eccentrically braced frame can be reduced, making EBF an ideal lateral resisting system in high-intensity seismic regions. However, repair of the structure is difficult and costly because the link is part of the floor beam. To improve the earthquake resilience of EBFs, this passage proposes a new type of link with a replaceable low yield point steel web and highstrength flanges, independent from each other and working in parallel based on the Chinese Sinology Center project. Experimental and numerical investigations are conducted, and the contents are as follows:(1) Quasi-staticcyclic loading of four replaceable link specimens are conducted. Experimental results show that the replaceable low yield point steel web will yield first under shear force, while the high strength flanges will remain elastic under certain rotation deformation. Preliminarily designed replaceable links can satisfy the bearing capacity demand of the Chinese Sinology Center project with hysteretic energy dissipation capacity. During the experiment, the warping deformation at the inner endplate of D type specimen and the slippage deformation at the connecting plate of K type specimen are observed, leading to the degradation of the bearing capacity and stiffness as well as the pinching effect of the hystereticcurve. These phenomenon indicate that the connection region has a significant influence on the mechanical performance of the whole replaceable link, which should be designed according to the compound force condition.(2) The refined finiteelementmodels of the replaceable link specimens are established through software ABAQUS, in which the high strength bolts are modeled as preloaded solid parts. The mechanical behaviors of the components under cyclic loading are well simulated including the inner endplate warping deformation of the D type specimens and the connecting plate slippage deformation of the K type specimens, and the numerical hystereticcurves are consistent with the experimental hystereticcurves on the whole.(3) The preliminarily designed replaceable links are optimized and the optimizing effect is validated both by the numerical and experimental investigations. The optimized replaceable links show full and stable hysteretic loops, indicating an excellent energy dissipation capacity. The results also show that appropriately designed endplate bolt connection will remain in the elastic range under shear force and moment. By reducing the web size, the high strength link frame can remain elastic under larger bending deformation, and the residual deformation after removing the low yield point steel web decreases significantly. The overstrength factors of short links with BLY160 replaceable web reaches 1.99 at least, which is higher than the value of 1.5 recommended by Popov, and the fracture at the weld connecting inner flange to the endplate is the main failure mode of the replaceable link. Meanwhile, numerical investigations are conducted to study the influence of major parameters on the link mechanical property, and the design method and suggestions of the link are proposed.(4) Based on the optimized replaceable link, a dual resilient eccentrically braced frame system is proposed, and its design principle is studied through theoretical analysis. Meanwhile, the multiscale finite element model of the resilient eccentrically braced frame is established in ABAQUS, in which the replaceable link is modeled as solid parts, coupling with columns, beams and braces meshed with beam elements through MPC constraints. The results of static pushover analysis and elastic-plastic dynamic analysis show that the stiffness of resilient EBFs with replaceable shear links is provided mainly by the frame columns, beams and braces, and the elastic stiffness of the replaceable link has little influence on the fundamental period and the whole earthquake action of the structure. High strength steel significantly improves the ability of the main frame to remain elastic under earthquake action, restricting the damage mainly on the low yield point steel web; the high strength steel main frame can still provide elastic restoring force after large deformation, dramatically deceases the residual deformation before and after the removing of the webs; under certain deformation, the structure will recenter to its initial position after removing the webs, making the replacing procedure of the webs convenient and swift. Under real strong earthquakes, well designed resilient EBFs will satisfy the elastic-plastic storey drift limitation well; the residual deformation of all the replaceable links will reduce to the allowable deviation of bolt installation under the restoring force of the main frame, making the replacing procedure of the damaged webs convenient and swift, significantly improving the resilience of the eccentrically braced frames.