Studv On Seismic Behavior Of SRUHSC Exterior Joints

Due to the full advantage of ultra high strength concrete(?C100 and structural steel,the steel reforced ultra high strength concrete(SRUHSC)structure has excellent seismic behavior,as well as high capacity.Hence,steel reinforced high strength concrete(SRUHSC)structures have the potential to be widely used in tall buildings in seismic regions.And the study of seismic performance of SRUHSC structure has attracted the attention of scholars both at home and abroad.Due to the brittleness and cross-section damage characteristics of ultra-high strength concrete,once the concrete cracks,the fracture surface is smooth and the aggregate bite action is weakened.Hence,the shear mechanism is affected.Therefore,from the material constitutive and the mechanism of shear level analysis,the seismic performance of steel reinforced high strength concrete(SRUHSC)composite structure is different from the ordinary steel reinforced concrete composite structure.The corresponding design index and design method should also be different.However,there are few researches on the seismic performance and shear mechanism of high strength concrete joints of steel bone,especially the research on the elastic and plastic analysis of such nodes has not been reported.The relevant specification of seismic design principles and construction measures for SRUHSC structure are also not make provision.That hindered the promotion and application of SRUHSC structure.Based on the National Natural Science Fund Project(No.51178078):"Study on Ductility-Based Seismic Behavior and Key Design Technique of Steel Reinforced Ultra-high Strength Concrete Frame System",this paper intends to carry out a systematic study on the seismic resistance of the high-strength concrete side joints of steel bone with the design parameters.It lays a foundation for the elastic-plastic analysis and design theory of frame structure.The detailed contents of this thesis are shown as follows:1.A research program on the seismic behavior of steel-reinforced ultra-high-strength concrete exterior joints is conducted herein by testing 22 specimens under a reversed cyclic loading profile,including two composite exterior joints:the steel reinforced ultra high strength concrete column-steel reinforced concrete beam and steel reinforced ultra high strength concrete column-reinforced concrete beam.This study analyzes the testing results in terms of the failure mode,cracks pattern,hysteretic curves,load-displacement relationship,ductility,energy dissipation capacity,strength and stiffness degradations.The main parameters analyzed included the axial compression ratio nt,stirrup ratio rsv in the joint core,and the ratio of structural steel in the joint core.The effect of the axial compression ratio on the shear capacity of the steel-reinforced ultra-high-strength concrete frame exterior joints characterized by a dividing point 0.38 is also proposed and verified according to the coulomb failure criterion and Mohr circle theory.Then the axial compression ratio limit and the minimum reinforcement ratio have been put forwarded;2.Through the analysis of steel reinforced web strain distribution,this paper puts forward the steel bone web effective width index and the mathematical expressions,which can more accurately reflect the axial compressive stress of steel shear mechanism and the elastic-plastic state of steel web.According to the principle of ductility design,the height of beam cross section under low cycle load is derived.Based on ultra high strength concrete constitutive model and the model of confined concrete research,the oblique compression bar angle and compressive bar height of the softening-compressive bar model,and compressive strength of the principal tensile strain softening coefficient have been calculated and adjustmented.Through the analysis of the shear strain of stirrups,the concept of the effective area of stirrup is introduced.The shear bearing capacity of stirrup is accurately calculated.And finally the formula of shear bearing capacity of SRUHSC exterior joints is deduced using the method of superposition.And it is concluded that different shear mechanism of steel reinforced high strength concrete contribution to the shear strength of SRUHSC exterior joints.3.Based on the experimental observation,a restoring force model for SRUHSC exterior joints is proposed,which is capable of considering the effect of the axial compression ratio and the ratio of stirrup on the hysteretic characteristics of the joints.It is showed thataxial compression ratio andthe ratioof stirruphave different degree of influence to the feature points of skeleton curve.The proposed restoringforcemodelis ingoodagreementwiththe test results and can be applied tononlinearanalysisof SRUHSCjoints.4.A nonlinear finite element analysis is conductedbased on the seismic performance of SRUHSC exterior joints,using the finite element analysis software ABAQUS.Thesimuted calculation of load-displacement skeleton curve and the shear bearing capacity of the specimens results agree well with the test results.