| The structures in salt lake regions,ocean engineering and chemical industry infrastructure are facing the dual challenges to ensure durability and seismic safety.Reactive powder concrete(RPC)is a new cement-based composite with high strength,toughness and excellent durability.The occlusal force of aggregates in cracking section are relatively weak because of no coarse aggregate in RPC.Axial compression load within certain limits can restrain the development of cracks in joint region,which can enhance the aggregate occlusal force in the reinforced concrete joint and increase the seismic shear bearing capacity of beam-column joints.However,the enhancement is little in RPC joint.After cracking,steel fibers across diagonal cracks can bear tensile stress by bonding,and reduce compression effective length of RPC,thus increase the shear bearing capacity of RPC.The cracking load of RPC frame joints will be different from that of normal concrete(NC)joints due to the higher tensile strength and cracking strain of RPC.So it is of great theoretical significance and practical worth to study the seismic shear bearing capacity of RPC frame joints.Cyclic loading tests of 12 exterior and 12 interior RPC beam-column joints were performed.Based on the observation on test phenomena,the analysis on mechanical mechanism and the reasonable consideration on influence parameters,the main results were as follows:(1)It was found that less RPC spalling occurred in joint region,while NC beam-column joints have larger area of surface spalling when shearing failure occurs.The diagonal cracking surfaces of RPC beam-column joint were smooth,while the cracking surfaces of NC beam-column joints were usually lumpy.(2)Under simultaneous vertical and horizontal loading,a set of coaxial and opposite forces in the diagonal position of joint were formed at the compression zone at the end of beam and column associated with the joint.The resultant forces were carried by a compression short column with a certain size in the joint region,which can be treated as diagonal struts.The essence of the shear failure of joint was compression failure of the diagonal struts.The role of stirrups was to provide effective constraint for the diagonal strut in joint region.The steel fiber across cracks can effectively reduce the calculated length of compressive RPC between the diagonal cracks.(3)The effects of stirrups at different positions in joint region were different.After cracking,the tension strains of stirrups were larger in the middle of the vertical height of the joint,smaller in the upper and lower part.Based on the test results,the mathematical relationship between the tension strain and vertical height of stirrups in joint region was presented,which was a breakthrough from qualitative to quantitative understanding for the distribution of stirrups strain in joint region.(4)Based on the test results of RPC beam-column joints,a formula for calculating the seismic shear bear capacity of the joints in the core region was established by using the equilibrium equation of the joint detachment.Due to the reason that the diagonal cracking surfaces of RPC beam-column joint were smooth,the influence of axial compression load on the occlusal force of concave and convex bite in the cracking surfaces was not considered.The mathematical expression about the tension strain of stirrups along the vertical height of the joint in the result(3)was introduced into the formula,and the influence of the position of stirrups on the seismic shear bear capacity of joint was considered reasonably.The horizontal component of the steel fiber tensile stress was fitted to consider the direct contribution of the steel fiber between the diagonal cracks to the shear bear capacity. |
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