钢和混凝土竖向混合结构阻尼特性研究

Damping behavior of vertical structures with upper steel and lower concrete components

下部混凝土结构与上部钢结构串联形成竖向混合结构(以下简称S/RC结构),由于建筑和结构上优势,该结构体系已在国内重大工程中得以应用。S/RC体系上、下部分材料不同,整体结构的阻尼参数难以确定,工程设计被迫采用钢材和混凝土两种不同阻尼参数进行计算。从阻尼矩阵和模态阻尼比两个方面研究分块Rayleigh模型和模态应变能模型这两个阻尼模型,并从理论上对模型的物理意义和应用基础进行分析。之后,以12层RC框架和12层S/RC框架的振动台试验为基础,从频域和时域两个层面对两个阻尼模型的有效性进行检验。结果表明,分块Rayleigh模型的阻尼矩阵为非比例阻尼,其难以用于常规的模态分析。模态应变能阻尼模型具有耗能等效的物理概念,且该模型在时域和频域内均具有更高的预测精度,建议在S/RC结构抗震分析中采用。

This paper presents an appropriate representation of the damping behavior of vertical structures with upper steel and lower concrete components （S/RC structure）. Two types of models are selected theoretically for the damping behavior of S/RC frames, which include an equivalent damping ratio model based on the dissipated energy of Modal Strain Energy （MSE） and a damping matrix model directly assembled by Rayleigh damping matrices for steel and concrete components. A 12-story S/RC frame and a 12-story RC frame are then designed and tested on the shaking table. Based on these tests, two expressions for measuring the damping behavior for the steel and the concrete component within the S/RC frame are derived, and the expressions are employed to form the damping expression for the S/RC frame in accordance with both of the damping models, respectively. Comparing the damping behavior represented by the two models with that identified in the shaking table tests for the S/RC frame, the damping models are assessed both in frequency domain and in time domain. The conclusions are therefore obtained based on theoretical analyses and experimental evaluation. The first model on assembled Rayleigh damping is not applicable to conventional modal analyses due to its non-proportional characteristics. The second damping model is formed on equivalence of the dissipated MSE of structure which embodies the essence of damping. In comparison with the test results, the second model gives better predictions on the damping behavior of the S/RC frame in both domains than the first damping model. In addition, complex modal analyses are used to predict seismic responses of the S/RC frame to exclude the errors due to non- proportional damping in conventional modal analyses.