Research On Seismic Performance Of Ultra-high Performance Concrete Filled Square Steel Tube Pier Column

Concrete-filled square steel tube composite pier column has the characteristics of simple joint structure,convenient connection and high bearing capacity,which is widely used in the field of bridge engineering.In recent years,with the increase of bridge span and the increase of vehicle load,ordinary concrete-filled steel tubular composite pier columns have been unable to meet the requirements of bridge bearing capacity and seismic capacity.Ultra-high performance concrete(UHPC)has ultra-high strength and ultra-high toughness and other mechanical properties.When UHPC materials are filled into steel tubes,it has better mechanical properties than ordinary concrete-filled steel tube composite pier columns.However,there are relatively few studies on the seismic performance and energy dissipation mechanism of concrete-filled steel tube pier columns with ultra-high performance concrete as the core.In this paper,the numerical analysis of UHPC-filled square steel tube pier column is carried out,and the seismic energy dissipation law of composite piers is studied.The sensitivity of composite piers to different influencing factors(axial compression ratio,slenderness ratio,and hoop coefficient)is analyzed and studied by using the orthogonal test method,and the optimal combination recommended value of UHPC-filled square steel tube pier column is given.The main contents include :(1)Based on ABAQUS software,a refined modeling method for UHPC-filled square steel tube pier column is proposed.The key modeling steps such as model meshing,element type selection,contact mode setting and constitutive model determination are analyzed in detail.Compared with the existing test results,the finite element simulation results are close to the test values,which verifies the accuracy and rationality of the modeling method in this paper.(2)Based on the principle of control variables,the influence parameters of seismic performance of UHPC-filled square steel tube pier column are analyzed and studied.The model of composite piers with different axial compression ratios(n = 0.3、0.4、0.5),slenderness ratios(λ = 20、24、29)and hoop coefficients(ξ = 0.32、0.43、0.54)was established.The effects of different parameters on the seismic performance indicators such as hysteresis curve,skeleton curve,ultimate bearing capacity,and cumulative energy dissipation are compared and analyzed,and the energy dissipation laws of composite piers are summarized.The results show that the ultimate bearing capacity and cumulative energy dissipation of composite piers are negatively correlated with the axial compression ratio and slenderness ratio,while the ultimate bearing capacity and cumulative energy consumption of composite piers are positively correlated with the hoop coefficient.(3)Based on the orthogonal test method,the seismic performance of square steel tube UHPC composite piers is optimized.The main influencing factors,such as axial compression ratio,slenderness ratio and hoop coefficient,were selected to carry out the three-factor and three-level orthogonal experimental design.There are three seismic performance evaluation indexes :ultimate bearing capacity,ductility coefficient and cumulative energy dissipation.The variance analysis and range analysis methods were used to carry out the sensitivity analysis on the influencing parameters of seismic performance of composite piers,and the optimal combination recommended value of UHPC composite piers with square steel tubes was given.The results show that within the scope of this study,the optimal design combination of UHPC-filled square steel tube pier column is : axial compression ratio(0.3)+ slenderness ratio(20)+ hoop coefficient(0.54).It has certain guiding significance and reference value for the design and construction of UHPC-filled square steel tube pier column.