Papers by Keyword: Curvature Ductility

Abstract: To research the impact of inner concrete filled steel tubular (CFST) on the reinforced concrete (RC) pier confined by stirrups, a Matlab program based on fiber model was written to calculate the moment-curvature (M-ϕ) relationship. The program was utilized to compute the M-ϕ relationships of three piers with same longitudinal bars and stirrups, and the three piers were an ordinary RC pier confined by stirrups、a high strength reinforced concrete (HSRC) pier confined by stirrups and a steel tube-reinforced concrete (ST-RC) pier respectively. The rules about bearing capacity of section and curvature ductility along with axial load N were deliberated by comparing the numeral results of three piers. The ratio of peak moment M_k to yield moment M_y was defined as super coefficient λ_s, and the disciplinarian of λ_s along with N was discussed. Participation factor ξ referred to the ratio of the moment provided by inner CFST to the total moment of ST-RC pier, and the laws of ξ affected by ϕ and N were researched. The results show that ST-RC pier has higher ductility and higher bearing capacity of section, and ductility decreases more slowly than other piers with the increase of N. λ_s of ST-RC pier is highest among three piers in most cases. On conditions of different N, ξ shows different variation trend with curvature ϕ up, and the maximum of participation factor ξ_max is reckoned to be not affected by N basically.

Abstract: Considerable amount of studies on the ductility and flexural behaviour of normal and high strength concrete elements under static load can be found in literature. However, most of the previous theoretical investigations on moment-curvature (M-φ) relationship of concrete elements to calculate curvature ductility and flexural capacity did not take account of the strain-rate effect on the material models. M-φ analysis of concrete elements under dynamic loading are often conducted with material models developed for quasi-static load by applying Dynamic Increase Factors (DIF) to the material properties to reflect the strain-rate effect. Depending on magnitude and duration of applied dynamic load, element stiffness and boundary condition strain-rate varies over the cross section. Thus, the application of DIF to modify peak material properties often fails to reflect the strain-rate effect reliably. The improvement of using material model which incorporated strain-rate in its constitutive equations has been explored in this study. The effects of reinforcement amount, grade and concrete strength on curvature ductility for different strain rates have been studied using material models which have strain-rate effects included in theirs formulation. Based on the parametric study, a simple formula to estimate curvature ductility for concrete elements under explosive loads (high strain-rates) has been proposed.

Abstract: Through simulation analysis of nonlinear finite element, research ideas on moment modulation coefficient of unbounded prestressed concrete (UPC) continuous beam is proposed ；Based on detailed analysis of the equivalent length of plastic hinge and curvature ductility, the two factors which influencing margin of moment modulation, calculating formulas of curvature ductility coefficient and moment modulation coefficient are established; Compared with the experimental data, the results which provided basic data for further research on plastic design of UPC continuous beam.

Abstract: Based on the equivalent uniaxial stress-strain relationship for the encased concrete in the square steel tube with binding bars, the fiber element analysis technique is used to conduct the load versus curvature curves for the square concrete-filled steel tubular (CFT) stub columns with binding bars subjected to eccentric load, and the results predicted by the program agree well with the experimental ones. The fiber element analysis program developed is then used to investigate the effects of varied parameters on the curvature ductility of square CFT stub columns with binding bars subjected to uniaxial or biaxial eccentric load, and the corresponding simplified formulas to predict the curvature ductility of the columns are put forward, respectively. The results predicted by the simplified formulas agree well with those predicted by the program.