Seismic Behavior Of Steel Reinforced High Strength Concrete Corner Columns Under High Axial Compressive Force

Columns near the bottom of a high-rise building are always subjected to highaxial compression force and biaxial bending. These columns are required to have highbearing capacity, exellent ductility and good seismic performance. It is one ofeffective ways to use steel reinforced high-strength concrete (SRHC) corner columnsto satisfy this requirement.In order to simulate the nonlinear behavior of a SRHC column under axial andbilateral loading, a nonlinear analysis program SECTION based on fiber model hasbeen developed. It has been found that in order to accurately simulate the behavior ofa SRHC column, the characteristics of the high strength concrete confined by stirrupsshould be considered. The previous experimental data of44axially loadedsquare-shaped stirrup-confined high strength reinforced concrete column specimenswere collected and analyzed. The concrete strengths are in the range of C50to C110.The stirrup characteristic values (λ) of the specimens are in the range of0.01to0.27.An analytical model named ZSA model, including an uniaxial stress-strainrelationship, the relationships between the peak compression strength fccand thecorresponding strain εccto the stirrup characteristic values λ were proposedrespectively.3large scale high-strength RC columns without concrete cover weretested under axial compression. The tested RC columns and some typical previoustested specimens were simulated using the proposed ZSA model. It has been provedthat the proposed ZSA model can predict the stirrup confinement well and can beused in prediction of nonlinear behavior of stirrup confined high-strength concrete.To study the seismic performance of SRHC corner columns,7large scalespecimens were loaded to failure under high axial compression ratio.4parametersincluding steel reinforcement ratio, steel cross section shape, angle of the lateralloading and the layerout of the steel in a column section were considered. The testresults proved that all specimens failed in flexural failure. The specimens’s lateraldrift ratios at peak load well satisfy the national seimic design code requirement. All specimens have good deformation capacity. It has been found that the improvement tothe column displacement ductility is not significant when the steel reinforcement ratiois small. The specimen with smaller width-to-thickness ratio steel plate behaved muchbetter. The specimens have a higher bearing capacity and an energy dissipationcapacity when they are loaded in-plane axial compression and lateral loading thanunder axial compression and bilateral loading. The effect from the layout of the steelin a RC column section on its bearing capacity is not significant but it will lead torapid decreasion of the column bearing capacity if the principle axial of the steel crosssection is different from the principle axial of the RC column section.Numerical simulations of the specimens have been carried out using the programSECTION and the software OpenSees. It has been proved that the proposed ZSAmodel can predict the stirrup confined high stength concrete column specimenbehavior more accurately. Parameter studies on the effect of the loading directionsbased on SRC4have been conducted. The numerical predicted results prove that theloading angles have much more influence on column lateral load bearing capacity.