Study On Effective Length Design Methods Of Rc.frame Columns

The element stiffness matrixes of concrete frame and truss structures are derived in this paper based on the principle of nonlinear finite element. Utilizing the method tat M-N- (I) relations of element are formed directly from physical properties of material, the influence of material nonlinearity and geometric nonlinearity are taken into account in the element stiffness matrix. Besides, one two-story one-bay RC. Frames and several members with flexure and axial force have been analyzed by the matrix and corresponding program has been developed, too. The results calculated by using the approach in this paper are found to be in good agreement with the experimental results. So the program provides an efficient means of theoretic analysis in studying nonlinear design method for reinforced concrete frames.This paper points Out problems existing in the determination of the effective length of reinforced concrete frame columns adopted in current concrete structure design codes of various countries and analysis the implication of effective length which determines the second order moment in critical sections of the column members. A nonlinear analytical computer program, which has been verified by experiments, is used to analyze the varying laws of second order moment with respect to different influential factors in critical sections of columns in the example of one seven-story two-bay RC. frames. Based on the arnendatory formula of the magnification coefficient for the eccentricity of standard column (hinged end column with equal end eccentricities) specified in China concrete structure design code, (GBJ1O-89), appropriate formula and varying laws of the effective length of column manbers in the analyzed example frames with the influential factors have been obtained. Moreover, a rudimentary conclusion that the effective length of frame columns specified in the new code seems to be safe and reliable in varying degrees in the examples a~ialyzed has also been acquired in the paper.