Seismic Bahavior And Design Of Structure With Self-centering Buckling-restrained Braces

Modern cities are supposed to recover swiftly from catastrophes, so thathuman life would not be greatly affected during and after such disasters. Thisneeds the infrastructures to behave far superior to what they do now. To this end,self-centering structures have been proposed. The recentering materials in mostexiting self-centering systems are Shape Memory Alloy (SMA) or somecomposite materials which are either expensive or hard to anchor, or both.Besides, energy dissipation of some self-centering systems is achieved thoughfriction and this may introduce two problems:(1) loosening of the prestressedbolts, which would lead to insufficient friction;(2) deterioration of the slidingface, which may change the prescribed friction force.A Buckling-restrained Brace(BRB) exhibits a stable energy dissipationcapcity, due to this feature, BRBs can significantly reduce the maximumdisplacement in buildings, which results in its popularity in StructureEngineering recently. However, the plastic behavior of a BRB often indicatescertain amount of permanent displacement in the structure after medium tosevere earthquakes.In order to circumvent these problems, this thesis focus on below issues:(1) A novel type of self-centering buckling-restrained brace which have bothadvantages of BRB and self-centering system has been proposed. By exploringthe mechanism of SCBRB, it is found that to ensure fully self-centering capacity,the self-centering bars should be endowed with sufficient elongation capacity aswell as considerably large elastic modulus which could afford stiffness in realstructures. It is opitimum that the strength of energy dissipation core be equal tothe prestressing force in the self-centering bars considering the balance btweenenergy-dissipating and self-centering capacitiy.(2) The primary parameters of a SCBRB system has been found and the therelationship between restoring force of a SCBRB system and the parameters hasbeen given. Using Response History Analysis (RHA), the comparison of SCBRBframes, BRB frames and Moment-resisting frames has been drawn and parameterstudy of the signifigant parameters of SCBRB multi-story buildings has been carried out. Based on that, primary design advice on parameters selection isproposed. To minimize the damages that would occur in frame buildings, theflexible frame buildings are preferable, which are featured by good elasticdeformation capacity, and this goal can be achieved by reducing the beams’rotation restricts to the columns. Pinned beam-to-column connections wouldpostpone the yielding of beams and columns, thus diminishing permanent drift ofthe building, and the benefit from that is more obvious in a huge earthquake.According to different deformation styles caused by various beam-to-columnconnections, effective story drift ratio has been proposed, which is a moreobjective way to evaluate the deformation in columns, when the beams do notstrongly restrain the rotation of the columns.(3) The application of Equivalent Linearization Methods(ELM) in SCBRBsystem has been studied. Based on the comparisons of displacements obtainedfrom two ELMs and Response History Analysis under20seismic records，thefollowing conclusion has been drawn: the ASD Method introduces smallerdisperseness, compared to the R-H Method; the ELM is much more accurate forSC systems than elastoplastic systems for displacement evaluation, due to theless obvious nonlinearity and plasticity in SC systems.(4) In order to obtain the statistical nonlinear displacement ratio (CR)spectra,453600SCBRB Single Degree of Freedom RHAs have been carried out.Then the CRformula has been regressed based on the enormous data. Throughthe CRformula, the nonlinear displacement of SCBRB systems can be caculateddirectly without iterations.(5) According to the CRformula, strength reduction factor(R) formula hasbeen obtained. A direct displacement-based design methodology for SCBRBsteel structures, according to R formula, has been proposed. The methodology isstraightforward, so iteration is unneccesary. The example shows that the designresult is conservative and can effectively deminish residual drift.