Study On The Compression Performance Of Steel Reactive Powder Concrete Columns

Reactive powder concrete(RPC)is a novel cement-based composite with high strength,high toughness as well as excellent volume stability.Accordingly,steel-RPC columns provide different compressive performances comparing with traditional steel-concrete columns.As a novel composite member,the investigations on steel-RPC columns are important for theoretical studies and engineering applications,and steel-RPC columns will have promising application foreground in the fields of super high-rise buildings and steel-structure strengthening.At present,there are extensive researches on steel-concrete columns,but few studies focus on steel-RPC columns.Besides,as for the constitutive relationship,previous investigations mainly focused on the constraint effect of the normal concrete other than the effect of constraint and strain ingredient on RPC.Hence,it is necessary to investigate the constitutive relationship of RPC in the steel-RPC columns,considering both the constraint effect of steel and stirrup,and the effect of strain ingredient.As for the composite members,researchers used to focus on the deterministic analysis instead of the stochastic analysis on the steel-concrete columns.Remarkably,researches on the stochastic analysis of steel-RPC columns have not been reported.Due to the nonlinearity and randomness of RPC,the nonlinear and random characteristics of steel-RPC columns significantly influence its compressive performances.Therefore,it is necessary to study performances of steel-RPC columns from a new perspective based on stochastic nonlinear analysis,which provides more knowledges for the composite structures design and the steel structures strengthening in the future.In this thesis,a comprehensive study on the compressive performances of steel-RPC columns at the level of materials and members is conducted based on experimental and theoretical researches,stochastic nonlinear analyses,and finite element analyses as follows.(1)Axial compression experiments,with three types of steel-RPC columns(RPC120,RPC150 and RPC180)are performed to measure the load-displacement relationship,the load-strain curve,the damage evolution,the load-transferring mechanism and the failure mode,and the ultimate bearing capacity.The results show that there are four typical loading stages in the process of axial compression,with the steel fiber preventing the development of the micro-crack,with the chemical bond,the mechanical friction and the dowel action constituting the basis of the compatible deformation between RPC and steel.(2)Eccentric compression experiments,with three types of steel-RPC columns(RPC120,RPC150 and RPC180)are utilized to measure the load-displacement relationship,the load-strain curve,the load-lateral displacement curve,the damage evolution,the load-transferring mechanism and the failure mode,and the ultimate bearing capacity.The results show that there are three typical loading stages in the process of eccentric compression.Besides,the failure mode exists under large eccentric compression with different damage distributions compared with normal members.(3)A novel constitutive model of constrained RPC,is established considering the confinement effects of hoops and steel,and the influence of eccentric loading.Then,the axial and eccentric compressive performances of the steel-RPC columns are analyzed using the fiber element method.From the results,the influences of the RPC strength,the steel content and the eccentricity,as well as the relationship between eccentric loading and bending moment are analysed,where the rationality of the proposed model is demonstrated.(4)Stochastic nonlinear analyses of the steel-RPC columns,are utilized to investigate the stochastic nonlinear response and the probability information during the axial and eccentric compressive processes based on probability density evolution method.Comparing the experimental curves and the stochastic nonlinear analysis,the accuracy of the stochastic nonlinear analyses method are verified both on the macroand meso-scales.(5)Finite element analyses of the steel-RPC columns,are employed to simulate the compression performance based on the proposed constitutive model of constrained RPC,where the simulated load-displacement curve,the damage distribution and evolution and the failure mode are satisfied with the previous experimental results.The agreement between numerical and experimental results further demonstrates the accuracy of the finite element model and the proposed constitutive model,and the numerical model is able to precisely simulate the constitutive model and the critical stages of the experimental process.