RC桥墩加载刚度退化及等效阻尼比试验

为揭示钢筋混凝土实心墩和空心墩的刚度退化规律及等效阻尼比，以剪跨比、配箍率和配筋率为设计参数，开展了7个方形实心墩和7个方形空心墩的低周往复加载试验。基于拟静力试验结果，探讨不同设计参数对实心和空心墩的滞回耗能及刚度退化的影响，建立了等效阻尼比与位移延性系数之间的关系，给出方形墩等效阻尼比的统一计算模型。通过文献中8组试验结果评估既有等效阻尼比公式，并验证所提出模型的适用性。研究结果表明：剪跨比对滞回耗能的影响不显著，而增加配筋率则可提高构件耗能能力；剪跨比对刚度退化的影响较配筋率和配箍率大，剪跨比越小的试件刚度退化越快；位移延性系数μ<3时，刚度退化系数随位移延性系数的增加呈指数下降，位移延性系数μ ≥ 3时刚度退化系数随位移延性系数的增加呈线性下降；等效屈服前等效阻尼比与刚度退化系数呈线性关系，等效屈服后等效阻尼比与刚度退化系数呈指数关系。既有等效阻尼比公式中，Priestley、程光煜和张艳青等所提公式的计算结果与试验值较为接近；较既有公式，所建议公式的计算值与试验值更为接近，适用于估算方形实心和空心墩的等效阻尼比。

Experiment on Loading Stiffness Degradation and Equivalent Damping Ratio of RC Piers

To explore the stiffness degradation mechanism and viscous damping property of reinforced concrete (RC) solid and hollow piers. Fourteen square solid and hollow piers were tested by cyclic loading with shear span ratio, stirrup ratio, and reinforcement ratio being design parameters. Based on the results of the quasi-static test, the dissipative characteristics and stiffness degradation were discussed considering the influence of different design parameters. The relationship was established between the equivalent damping ratio and displacement ductility ratio, and a unified formula for the equivalent damping ratio was obtained for square solid and hollow piers. Eight tests in the literature were applied to evaluate the existing formulas of equivalent damping ratio. The applicability of the proposed formula was validated by the experimental results. The research shows that the effect of aspect ratio on the hysteretic energy is not significant. Increasing reinforcement ratio indicates increased dissipation capacity. The aspect ratio exerts greater influence on stiffness degradation than the ratio of the longitudinal and lateral steel do. The smaller shear span ratio, the faster stiffness degradation for the specimens. When the stiffness degradation ratio was less than 3, it decreased exponentially with the coefficient of displacement ductility. If the ratio was equal to or larger than 3, it decreased linearly with the ductility factor. The equivalent damping ratio increased linearly with the stiffness degradation before the state of equivalent yield. Then, the coefficient of degradation decreased exponentially after the yield state was reached. Among the existing formulas of equivalent damping ratio, the results of Priestley, Cheng, and Zhang were relatively close to the tests. Compared with the existing formulas, the results of the proposed model were closer to the tested equivalent damping ratio of square solid and hollow piers.