低周反复试验轴力加载装置的系统摩擦力

在柱、剪力墙等的低周反复加载试验中，与施加轴压力的竖向作动器相连的钢铰轴处或滑动导轨处存在的摩擦力会导致加载水平力的测量结果不同程度地较真实值偏高。通过试验和有限元计算，分析了该摩擦力的规律和量化取值。为了消除材料非线性并准确考虑几何非线性的影响，设计两个型钢柱进行了材料弹性状态下的低周反复试验，并在OpenSees平台上建立了能够准确计算二阶效应的有限元模型。根据试验测量结果、有限元分析结果对该试验的轴力加载装置引起的摩擦力进行计算，研究了摩擦系数的取值方法，并考察了摩擦力对柱试验结果的影响。研究结果表明：由轴力加载装置引起的摩擦力主要受轴压力值影响，柱顶位移的影响较小；随着轴压力增大，摩擦力增大、摩擦系数变小；最大摩擦力、最小摩擦系数均趋于较稳定的取值；对于轴压力为350~900 kN的钢筋混凝土柱，由该装置摩擦力引起的低周反复试验的柱顶水平力测量结果误差约为5~13 kN。

Research on system frictional force of axial force applying devices in cyclic loading test

In the cyclic loading test of column or shear wall with the axial compression load, frictional force exists in the roller of steel hinges or the sliding rail, which is connected to the vertical actuator for applying axial force. The measurement of lateral load would be higher than its actual value due to this friction. On the basis of experimental research and finite element simulation, the variation characteristics and quantization method of the friction were investigated. In order to eliminate the influence of material nonlinearity and calculate geometric nonlinearity accurately, two steel columns were designed and cyclic loading tests under elastic situation were carried out. Besides, a finite element model which can accurately calculate the second-order effects was established on the OpenSees platform. Based on experimental and numerical results, the frictional forces were calculated, the method of determining the friction coefficient was proposed, and the influence of friction on the experimental results was evaluated. It was revealed that the frictional force caused by the devices for applying axial force was mainly affected by the axial compression force, while the top displacement of columns was of weak influence. As the axial compression force increases, the frictional force increases and the friction coefficient decreases. However, the maximum frictional force or the minimum friction coefficient converges. In cyclic loading test of the reinforced concrete columns with axial force of 350~900 kN,the measurement error of column top horizontal force caused by friction is 5~13 kN approximately.