Coefficient of curvature influence in calculation of bearing capacity of reinforced concrete columns

In calculation of the bearing capacity of the eccentrically loaded reinforced concrete columns, in order to consider the second order effect of bending moment in the section, the effect of bending moment enlargement coefficient is used, which includes two factors, i.e. the curvature influence coefficient of eccentricity ζ1 and the curvature influence coefficient of slenderness ratio ζ2. Some differences exist in the calculation methods of these two curvature influence coefficients among the current China design codes such as the GB 50010-2010 'Code for design of concrete structure' and JTG D62-2004 'Code for design of highway reinforced concrete and prestressed concrete bridges and culverts'. Through the bearing capacity tests of 14 reinforced concrete columns, the column bearing capacities obtained from test results were compared with those calculated by code methods. The results show that the calculated bearing capacity of the specimens by the GB 50010-2010 are lower than the test ones due to the ζ2 is deleted in the code, while the calculation method of ζ1 in JTG D62-2004 is not rational since the calculated bearing capacities are larger than the test ones and tend to be unsafe for structures especially when the eccentricity is small. Based on the experimental research, parametric analyses by the finite element method were carried out, and the calculation formulas for ζ1 and ζ2 were proposed. The accuracy of the proposed calculation method was verified by the collected test results of the references.