Study On Utility Design Methods Of Second-Order Effect For Multiple-Story And Tall Reinforced Concrete Buildings

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-Δeffect and the later P-δeffect. In the design of frame structure,shear-wall structure,wall-frame structure and etc, second-order effect should be considered. Though till today researchers all over the world have made great progress in the field of second-order theories and its design methods, there are still remaining lots of problems that need to be clarified and further study.First,the paper has listed and analysed almost all the existed methods which are used to calculate the second-order effect of structure, by doing so, the hypothesis and the theory the methods above incorporated and also their application scope are well shown. These include the story magnification factor method,method presented by Perrez,method base on the energy principle and method decided by formula 5.1.5-3 in《Technical specification for concrete structures of tall building》JGJ 3-2002 and ect. The above are all simplified methods that incorporate the principle of additional effect of structure when considering its second-order effect. Besides, the paper also discussed the linear & nonlinear second-order analysis methods which are run by computer.Then, analysed by theory and verified by examples, the paper has presented a criterion for foretelling the law of the change of moment in the columns and beams in the closed-frame unit before the P-δeffect is taken under consideration. Following above, P-δeffect in multiple -story &bay-frame, using the traditional eccentricity magnification factor (also calledη-l0 method) is studied, referring to the results of relative experiments, the paper has presented the plans of how to decide the effective length l0 and the adjustment factor of eccentricity Cm .Third, due to problems presented by personnel from the engineering application to the team of the building code management last year that the effective length calculated from those fitting formulas from the code when using theη-l0 method for considering frame structure's P-Δeffect is unreasonable in some circumstances, the paper found out that there is some deficiency in the fitting formulas from the code and presented two sets of plans aiming at perfecting the fitting formulas for code...