Static Behavior Of Concrete-filled Corrugated Steel Tubular Members

As a innovative composite member,the concrete-filled corrugated steel tubular(CFCST)member can effectively solve the corrosion and maintainance problems of outdoor structures,which retains the specific behavior and construction convenience,and thus has strong adaptability and broad application prospect in civil engineering main structures with high durability requirements,such as municipal bridges,industrial buildings,wind turbine towers and large-power transmission towers.Currently,the research of the mechanical behavior of CFCST is not yet systematic and still in its early stage in general,and there is no exsisted standard in practice.This study is conducted focusing on the fundamental static behaviors of CFCST members,including the behaviors of CFCST section under axial and eccentric compression,stability and behavior of CFCST slender columns,torsional behavior,to reveal the confinement mechanism and composite work mechanism of CFCST.The details are in the following:(1)Behavior of concrete-filled corrugated steel tubular short column under axial compression and confinement mechanism.The experimental program of 21 axially compressed short columns including 12 CFCSTs has been conduncted,whose main varible factors are confinement factor,load carrying mode in both ends and types of specimens.Based on the test,the failure mode,load bearing capacity,stress of corrugated steel tube(CST),etc.has been analyzed.The uniaxial stess-strain constitutive model has been established for the finite element models in ABAQUS.Then,solid-shell nonlinear finite element models(FEM)have been established to predict the axial behavior of CFCST section.As well,the non-uniform confinement along the longitudinal direction of CFCST member is revealed,and the distribution of local confining stress is confirmed by deriving the theoretical formulas.The parametric analysis has been carried out on the geometry and material strength to quantify the equivalent confining stress of CST.By establishing the numerical fiber model,the parametric analysis is conducted on cross-sectional axial load bearing capcities of CFCST.Based on the design method for tubed reinforced concrete,a design method for CFCST is developed to predict the cross-sectional axial-load bearing capacity.(2)Behavior of concrete-filled corrugated steel tubular short column under eccentric compression.The experiment of 18 short columns under eccentric compression and 3 beams under pure bending has been carried out,whose parameters are load eccentricity,confinement factor and specimens’ types.The failure modes,load-deflection curves,as well as distribution and development of strain at different corrugation location(crest,trough and middle)in compression and tension zone are analyzed.To study the eccentrically compressed behavior of CFCST section,the solid-shell finiteelement models are established.The non-uniform confinement mechanism across the cross-section and along height has been revealed,and the quantitative formula of the equivalent confining stress across the cross section is also presented.After that,the uniaxial stress-strain model of core concrete is developed considering the nonuniformity of confinement.The non-linear numerical fiber model has been also established to systematically analyze the load bearing capacities of CFCST section under eccentric compression,where the non-uniform confinement and strain concentration are taken into consideration.Finally,a design method is proposed to predict the compression-bending strength of CFCST sections.(3)Stability behavior of axially and eccentrically compressed concretefilled corrugated steel tubular members.An experiment has been carried out on 8 groups(24 in total)slender columns with various slenderness ratios and eccentricity ratios.The deformed shape,characteristics of failure,loadmid height deflection relationship curves,as well as axial force-strain of CST curves are analyzed.The parametric analysis has been conducted based on the fiber model,and the quantitative fomulas are proposed for calculating axial compression stability coefficient,bending moment amplification coefficient and eccentricity adjustment coefficient.Thus,the design method for CFCST slender columns under axial and eccentric compression has been proposed by considering the secondary effect.(4)Torsional behavior of concrete-filled corrugated steel tubular members.By designing a loading system suitable for pure torsion,the torsional behavior of 6 specimens are investigated.The analyzed factors are orientation of torsion,load carrying mode of CST under torsion,and type of member.The torque-twist angle curves and strain of CST versus twist angle curves have been measured and analyzed.Considering the practical interlock of lock seam,on which the occlusal shear stress was measured and the bond-slip constitutive model has been developed.By developing the pratical corrugation and lock seam of CST,the torsional finite element model has been built for CFCST members.The development of stresses of CST and core concrete,as well as that on contact interface,have been investigated.The cooperative torsional mechanism of CFCST section has been revealed.Combining the theoretical derivation and parametric analysis,the simplified design method has been proposed for the torsional resistance of CFCST member.