The Discussions About Second-Order Effect Of Reinforced Concrete Frame

Second-order effect is referred to the additional force and displacement of the structure members and bars that have interbedded displacement and deflection along its axis caused by its axial force. Usually, the former case is called P—△effect and the later P—δeffect. In the design of structure, second-order effect should be considered. Although research on the theory of second-order effect has been made progress recently, for frame structure, there remains a series of important problems needed to perfect, in order to improve the design methods which are now ambiguous in conception and reply heavily on empirical experience.First, due to the inadequate researches on the regular pattern of P-δeffect in frame at home and aboard, according to the basic examples, the papar has analyzed the factors and degree of influence of P-δeffect in the closed-frame unit, the important is the rule of the change of influence due to the Second-order moment on end-column of closed-frame unit toward the total moment.Then, integrate with second-order effect theoretical analysis, the papar has analyzed the no-sway frame structures under P-δeffect of which can't be ignored on the structure and received the formula of no-sway frame column slenderness ratio limitsλe consider with P-δeffect; in addition, analyzed the factors of sway frame structures under P-δeffect and whether the slenderness ratio limitsλe, was essential in engineering.Third, due to the building code calculated the P-△effect of frame structures with the method ofη-l0, in some cases, the calculated moment magnification factorηwas inconsequence, the paper perfected a more reasonable formula.Finally, the paper has done modal analysis,response spectrum analysis and time history analysis of calculation and analysis, by elastic second-order theory and a reinforced concrete frame structure example with consider P-△effect and not consider P-△effect, to examine the impact of different factors in the results, and propose some useful conclusions for the structure design.