Research On Seismic Performance And Design Method Of FRC Diagonally Reinforced Coupling Beams And Coupled Shear Walls

Coupled shear walls are complex yet attractive lateral load resisting system. Thebest yield mechanism of coupled shear walls subject to major earthquake is damage tothe coupling beams occurs prior to the plastic capacity of the system being achieved. Inorder to make coupled shear walls achieved to their best yield mechanism, the beamsmust have sufficient ductility and energy dissipation capacity, and the coupled shearwalls must be designed reasonable. Therefore, based on the seismic performance studyof FRC diagonally reinforced coupling beam with small span-to-depth，design methodsof coupled shear walls are proposed. Major achievements of the dissertation are asfollows：(1) The four FRC diagonally reinforced coupling beam specimens with smallspan-to-depth and one common concrete diagonally reinforced beam were tested underreversed cyclic lateral loading. The specimens’ failure process, failure modes, bearingcapacity, deformation capacity and energy dissipation are studied. The results showedthat FRC can increase the bearing capacity, ductility and energy dissipation of thecoupling beams, and the FRC coupling beams already has a high shear capacity anddeformation capacity, as well as good resistance to damage before the main diagonalcracks formed, which have been able to meet the needs of the bearing capacity anddeformation under strong earthquakes and can continue to use without repair or a littlerepair.(2) Using the effective finite modal，the effect of FRC compressive strength,span-to-depth, section width, diagonally steel bars reinforcement ratio, stirrupsreinforcement ratio, vertical forced steel bars reinforcement ratio, distribution steel bars reinforcement ratio and embedded length on the seismic behavior of the FRC diagonallyreinforced coupling beam is studied. The results show that span-to-depth, diagonallysteel bars reinforcement ratio and section width are major factors which impact on theseismic behavior of the coupling beams.(3) On the basis of mechanics characteristics of FRC diagonally reinforcedcoupling beams with small span-to-depth and tensile strain hardening characteristics ofFRC, tie-strut model is used based on reasonable assumptions, a nonlinearforce-displacement theoretical model which can predict force-displacement skeletoncurve is put forward. Then, the simplified formula of the beam’s shear cappacity isproposed using the theoretical model and the effective length of embedded of precastcoupling beams is proposed using the force and the constraint moment balanceconditions.(4) The upper and down limits of the coupling ratio of the coupled shear walls withFRC diagonally reinforced coupling beams is studied, then the reasonable ratio is givenwhich from30%to64%, and it must be meet the limit value of shear wall’s axialcompressive ratio. Then, based on the continuous connection method, the performancecontrol method of coupled shear walls is proposed. Firstly, the coupling beam’s sectionsize is determined through controlling the coupling ratio in a rational range to make thewall meet the demand of the displacement ductility. Secondly，the base shear isdetermined through controlling the roof drift and inter-story drift. Finally, the demand ofthe relative vertical deformation at coupling beam ends which meet the coupling beamductility demand is determined, and then the amount of stirrups in the coupling beam isdetermined by the relative vertical deformation and the requirement of the couplingbeam’s shear capacity.(5) Based on the idea of yield mechanism control of coupled shear walls andperformance design, the performance design method based on the best mechanism ofcoupled shear walls is proposed. First, yield mechanism and target drift under the givenearthquake level is selected, and the design base shear is calculated by equating energyequation, and a lateral design force distribution consistent with the intended yieldmechanism is calculated. The shear force and required plastic moment of the couplingbeams are determined by the coupling ratio. Finally, in order to achieve the intended mechanism and performance, the required plastic moment of wall piers in the first storyis determined by using the energy balance equation under the intended yield mechanism.The elsto-plastic time-history analysis shows the obtained results are reliable.