The Research On Several Second-Order Effect Problems Of RC Structures

Second-order effects belonging to geometrical non-linear problems are the additional effects caused by axial forces applied to deflecting member bars or vertical loads working at sway structures, which should be considered in accurate structural analysis. Comprehensive research has been made for many years in foreign and home-area. In order to complement and improve the system of structural analysis and design relating to second-order effects, hereinafter some tasks have been completed by request.1. The regular pattern of second-order effects according to numerical analysis results in non-sway closed cell frame-columns is reviewed in this paper. The second-order internal force equation and the additional displacement method based on the turn-angle equation are provided in second-order effects analysis. The analytic solution of second-order effects in non-sway closed cell frames is solved by this method, which has proved that the regular pattern of second-order effects in non-sway closed cell frame-columns is exact.2. The conventionalη? l0 method is the major structural design method considering second-order effects of reinforced concrete bent-columns, and its accuracy mostly depends on the rationality of effective length l0 . The rational value of l0 has been discussed in this paper. The disadvantage of the initial-parameter method deriving the effective length l0 of bent-columns in Chinese Standard has been pointed out, and the improvement has been made. According to the second-order elasticity analysis of single-story single-span bent frames, the effective length l0 suggestion of bent-columns have been made in this paper.3. The simplified structural analysis and design method employing stiffness reduction of member bars, has been accepted by Chinese Standard, in which second-order effects already been considered through elastic finite element analysis. According to the non-linear finite element analysis of several single-story single-span bent frames, the stiffness reduction factor of bent-columns has been suggested in this paper. And the rationality of this factor has been proved by comparison of the internal force in bent-columns and displacement of bent frames in second-order elasticity analysis and non-linear finite element analysis.