Experimental Study On Seismic Performance Of Exterior Reinforced Reactive Powder Concrete Frame Joints

Reactive Powder Concrete(RPC),as a new cement-based composites,has obvious advantages in features such as strength,toughness,durability and environmental property compared with ordinary concrete and high-strength concrete.It is an indisputable fact that applying RPC to pouring core areas of frame joints can solve the crowed state of stirrup configuration under the premise of ensuring seismic performance of members and the exterior frame joints only have unilateral beam constraints,which of the damage in the earthquake are more serious than the interior frame joints.Therefore,to study seismic performance of exterior reinforced reactive powder concrete frame joints has important theoretical and practical significance.In this paper,seven exterior reinforced reactive powder concrete frame joints were designed,fabricated and tested under quasi-static loading.Mechanical behaviors of reinforced reactive powder concrete frame joints were acquired through investigating all failure processes from initial cracking to failure and distribution of cracks at all levels of the load and displacement of each specimen.Experimental results indicate that,the failure process of reinforced reactive powder concrete frame joints,i.e.,initial cracking stage,thorough cracking stage,ultimate stage and failure stage is basically similar to that of other reinforced concrete frame joints,while the failure characteristics of it stands in stark contrast to that of other joints.Load-displacement hysteresis curves and skeleton curves of reinforced reactive powder concrete frame joints were obtained,and the influence of factors including stirrup ratio in core,longitudinal reinforcement ratio in beam,longitudinal reinforcement strength in beam and column and axial compression ratio on seismic performance of frame joints was analyzed through referring to several coefficients,such as hysteresis behavior,ductility,energy dissipation and stiffness degeneration.Experimental results show that,adding of stirrup ratio in core can increase ultimate shear bearing capacity,ductility and energy dissipation capacity of specimens in different degrees,but increases of which are inconspicuous when stirrup ratio in core adds a little.Therefore,this paper suggests when applying RPC to pouring core areas of frame joints,the amount of stirrup should correspondingly increase maximally,but Configuration of stirrup has to follow related design specification and avoid the crowded state,of course.Adding of longitudinal reinforcement ratio in beam can increase ultimate shear bearing capacity of specimens,but ductility and energy dissipation capacity decrease significantly when not stirrup in core.Increase of longitudinal reinforcement strength in beam and column but no stirrup in core can make core resistance of specimens more weak than beam and column and occurrence of brittle damage which only has poor ultimate shear bearing capacity,ductility and energy dissipation capacity.When stirrup in core,ultimate shear bearing capacity increases but ductility and energy dissipation capacity decrease with axial compression ratio adding from 0.3 to 0.5.Based on the experimental study,the calculation model and formula for the shear bearing capacity of exterior reinforced reactive powder concrete frame joints under the combined actions was proposed,in which the simplified softened strut-and-tie model was adopted and the favorable contribution of pullout resistance of steel fibers to the shear bearing capacity was considered.The analysis of the exterior joints hysteretic curve and skeleton curve was also acquired,the restoring force model of exterior reinforced reactive powder concrete frame joints,which included a three-line model of skeleton curve and stiffness degradation rule,was also proposed,in which data fitting and theoretical analysis were adopted.