| Green high-performance fiber-reinforced cementitious composite(GHPFRCC)is a new type of advanced cementitious composite that is developed from PVA-ECC by replacing 60% cement with fly ash.GHPFRCC has tensile strain hardening behavior and high tensile ductility and toughness.The use of GHPFRCC can effectively reduce the reinforcement ratio in the core of beam-column joints,improve the deformability of the plastic hinge zone,and increase the energy dissipation of the joint.Basalt fiber has high tensile strength and high resistance to high temperature and corrosion,and thus is promising for repair of beam-column joints after exposure to fire.This thesis presents a post-fire retrofit and cyclic testing of six beam-column joint specimens.The main research contents of this thesis are introduced as below.(1)Six beam-column joint specimens were designed and fabricated in the laboratory,including five GHPFRCC specimens,and one conventional reinforced concrete specimen.The fire resistance of the joints was evaluated through structural fire testing.Post-fire repair was conducted for the tested specimens,which were then tested to failure under cyclic loading.(2)Fire testing of four GHPFRCC specimens and the conventional concrete specimen was conducted in ISO834 fire.Explosive spalling occurred at the beam-column joint of the conventional concrete specimen,while explosive spalling was not observed in the GHPFRCC specimens,in which GHPFRCC could still protect steel reinforcement from fire.According to the measurement results from thermocouples,different specimens had similar temperature distributions.That is,temperature decreases along the beam and column towards the beam-column joint,and the surface temperature(> 400 °C)is higher than the inner temperature.Thus,the exterior surface is subjected to serious material deterioration and needs to be removed in repairing.After experiencing combined fire and mechanical loading,significant deformation was generated and increased the difficulty in retrofitting.(3)The beam-column joint specimens were repaired using GHPFRCC and strengthened using basalt fiber reinforced polymer fabrics,based on the examination of the fire damages in thespecimens.Some fractured reinforcing bars were welded.The retrofitted beam-column joint specimens were tested under cyclic loading.The hysteretic curves and skeleton curves of each component were obtained to analyze the stiffness and energy dissipation of frame joints.The following key findings were obtained:(1)The skeleton curve of the reinforced GHPFRCC is the same as that of the undamaged GHPFRCC and will not cause excessive changes in the dynamic performance.(2)GHPFRCC protection layer replacement reinforcement can improve the cracking form of the core area of the frame joint.(3)The distribution ratio of the core area and the pouring material have little effect on the stiffness degradation,and the stiffness degradation trend of the frame joint after reinforcement is the same as that of the original structure.However,if the damaged components are to be restored to their original stiffness,other reinforcement and reinforcement measures are also required.(4)The attenuation of bearing capacity of the GHPFRCC frame joint is not serious,which ensures the stability of the seismic performance of the components.(5)Frame joints generate a certain amount of steel slip in the core area of the late loading joint.In general,the design requirements for “Strong-column Weak-beam” can be guaranteed.(6)The annular hoop fiber cloth of the frame beam column can effectively suppress the lateral deformation of the component.The diagonal cross-fiber cloth can improve the shear resistance of the core area of the joint,and the application of BFRP improves the seismic performance of the component. |
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