| Under vertical loading, two categories of second-order effects exist in deformed structure, i.e. P -Δeffect and P -δeffect. There are many studies on static second-order effects; however, the researches towards dynamic second-order effects are less concerned, in addition, the related studies are limited to P -Δeffect aspect. This paper has inquired into the refined analysis models of RC slender column structure and dynamic second-order effects. The main contents are as follow.According to flexibility method theory method and fiber model, a new refined model has been established, which not only accurately evaluates P -Δeffect and P -δeffect but also realizes separate calculations of them. As a result, it is entirely possible to study on the law of dynamic second-order effects and the influence from P -δeffect on P -Δeffect through using same element model. And the refined model is proved accurate and efficient by numerical validation and comparative analysis.The strut-and-tie model has been introduced due to the shear deformation of beam-column joint, and a new method has been put forward which shows the transferring shear force mechanism of beam-column joint core. The paper has compared the shear stress-strain relationship curves of beam-column joint core resulted from other methods with those from experimental results, it finds that the results based on the new method is more closed to the experimental results.In the part of studies on the dynamic second-order effects of SDOF system are carried out step by step: firstly, in the light of structures’P -Δeffect and P -δeffect, the calculation formula for reduction coefficient of lateral stiffiness is deduced under horizontal earthquake loading. Based on these, the formulas of general and standard response spectrum with dynamic second-order effects were offered, the reliability and accuracy of theoretical formula were validated by numerical calculation. Secondly, the proportion of P -δeffect accounts for second-order effects is achieved through static and dynamic analyses, the distinction between static and dynamic second-order effects and the factors influencing the two are confirmed, and structural period and frequency spectrum characteristic of ground motion have significant impacts on the two except stability factors. Thirdly, the impact of vertical ground motion on structures’horizontal response is regarded as that of varied-axial-force on horizontal seismic response in this paper, the motion equation in which structural second-order effects is counted has been established as horizontal and vertical earquake take effect simultaneously, the factors of vertical ground motions influencing structural dynamic second-order effecs have been figured out by parametric analysis. Fourthly, the different degrees of material nonlinear on dynamic second-order effects were investigated; furthermore, the possibility of adopting stiffness reduction to assess the impact of material nonlinear was discussed. Finally, 5 groups of specimens have been designed; plate loading test with and without second-order effects and shaking table test under horizontal earquake or horizontal and vertical earthquake in combination have been completed, the results indicate that the methods for considering the dynamic second-order effects are appropriate and accurate.In the part of study on dynamic P -Δeffect of MDOF system, the problems existing in the methods of designed programs and criterions considering P -Δeffect are analyzed, particularly, the method of equivalent horizontal force regarding second-order effect and“fictitious column”method are discussed. This paper is theoretically showed that the fictitious column method can be used to calculate the P -Δeffect of shearing and flexural structure approximately in static and dynamic analyses; moreover, the two simplified methods with P -Δeffect were presented: modal analysis response spectrum method and equivalent base shear method, the two methods are proved practical and reasonable by comparing the calculated numerical results. |
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