Research On Seismic Performance Of Fiber Reinforced Concrete Coupling Beams With Small Span-to-Depth Ratio And Frame-Shear Wall Structures

The coupling beam is an important energy-consuming component in the shear wall structures and frame-shear wall structures.Due to the requirements of the building function and the structural stiffness,the coupling beams often have small span-to-depth ratio and high shear-compression ratio.When the structure is subjected to a major earthquake,the coupling beam is prone to brittle shear failure prematurely,which leads to the failure to meet the requirements of seismic ductility and energy consumption,and the failure to play its role as the first line of defense against earthquakes.Fiber reinforced concrete(FRC)is a new type of green building materials with high toughness and high energy consumption capacity,which exhibits significant strain hardening and multi-crack development characteristics under tensile and bending loads,and can improve the seismic and shear performance of reinforced concrete structures.Therefore,FRC coupling beams with small span-to-depth ratio were designed and fabricated,and the experimental study and theoretical analysis of the seismic performance were carried out.On this basis,the seismic performance of the frame-shear wall structure with FRC used in the expected damage parts was also further evaluated.Main contents and achievements of the dissertation are as follows:(1)The three FRC diagonally reinforced coupling beam specimens with small span-to-depth ratio were tested under reversed cyclic lateral loading.The specimens' failure process,failure modes,bearing capacity,hysteretic energy dissipation,stiffness degradation and ductility were analyzed by comparison with the previous test results of the research group.The results indicate that it can significantly improve the bearing capacity,ductility and energy dissipation performance of the diagonally reinforced coupling beam by using FRC instead of common concrete.Reasonable width of the section and number of stirrups of the coupling beam,and the addition of crossties on the diagonal reinforcements can effectively restrain the diagonal reinforcements and the core FRC,which can improve the failure mode and damage resistance of coupling beams.(2)The seven FRC conventionally reinforced coupling beam specimens with small span-to-depth ratio and one common concrete conventionally reinforced coupling beam were designed and tested under reversed cyclic lateral loading.The influence of the span-to-depth ratio,stirrup spacing and the strength of FRC on the specimens' failure process,bearing capacity,deformation capacity,energy dissipation and stiffness degradation rule were studied.The results show that FRC can improve the bearing capacity,ductility,energy dissipation capacity and the limited values of shear-compression ratio.With the increase of the span-to-depth ratio and the ratio of stirrups,the failure modes of FRC conventionally reinforced coupling beams with small span-to-depth ratio gradually change from brittle shear failure to flexural-shear failure with certain ductility characteristics.The FRC coupling beam exhibite good damage resistance,and can meet the requirements of bearing capacity and deformation demand under major earthquakes,which can be continued to use after the earthquake without or slightly repair.(3)According to the mechanics characteristics of FRC coupling beams with small span-to-depth ratio,considering the strain hardening characteristics of FRC,the shear capacity of FRC coupling beams with small span-to-depth ratio was carried out based on the softened strut-and-tie model,the modified compression-field theory and truss-arch model,respectively.The analysis model and calculation method of shear capacity of FRC coupling beams with small span-to-depth ratio were established.Based on the standard formula,the simplified calculation method of the shear capacity of FRC coupling beam was proposed.The results indicate that the calculated values of the shear capacity of the FRC coupling beams with small span-to-depth ratio are in good agreement with the experimental values,which can reasonably reflect the shear performance of the FRC coupling beams.(4)Based on the combination of theoretical analysis and experimental regression,the calculation method of the characteristic points in the three-fold line skeleton curve of the FRC coupling beams with small span-to-depth ratio was proposed.At the same time,considering the influence of the span-to-depth ratio and the ratio of stirrups,the calculation method of the unloading stiffness and strength degradation coefficient was proposed,and the hysteresis rules of the restoring force model was given.The results indicate that the calculated results are in good agreement with the experimental results according to the proposed restoring force model,which can better reflect the restoring force characteristics of FRC coupling beams with small span-to-depth ratio.(5)A 12-layer reinforced concrete(RC)frame-shear wall structure was designed according to Chinese current design specifications.FRC was applied to the potential damage parts of the frame-shear wall structure,and the dynamic elastoplastic analysis of FRC frame-shear wall structure and RC frame-shear wall structure were constructed using Perform-3D software,respectively,and the seismic performance of frame-shear wall structure by using FRC in the potential damage parts was studied.Then,the seismic fragility analysis of FRC frame-shear wall structure was carried out based on the incremental dynamic analysis method,and the probability of exceedance of the FRC frame-shear wall structure under different performance levels were obtained.The results show that the application of FRC in the potential damage parts can improve the seismic performance of the frame-shear wall structure,and the damage degree is relatively light under the earthquake,which can meet the seismic fortification requirements of the structure under major earthquakes.