重载列车作用下桥墩-桩基竖向动荷载特性试验研究

为探明大轴重、长编组和高密度重载列车作用下桥墩和桩基承台顶的动荷载特性,开展不同车速和轴重条件下的桥墩-桩基体系竖向动荷载响应现场试验。分析桥墩动荷载曲线的时域、频域特征,采用Kolmogorov法对动荷载幅值进行正态性检验,建立列车参数与动荷载频域特征的联系;基于3σ原则对不同敞车作用下的动荷载特征值(均值、均幅值和均峰值)进行统计,结合实测数据建立重载列车作用下的墩顶动力系数计算公式,并提出墩顶和桩基承台顶的荷载谱公式及其参数取值。结果表明:动荷载响应在时域上可分为快速增加,周期波动和快速衰减3个阶段,在频域上服从倍频规律和幅值调制效应,0～5Hz频段激振对动荷载起控制作用;动荷载幅值服从正态分布,动荷载均峰值和振动能量沿墩身衰减明显,动荷载均值和均峰值随轴重增大而增大,均幅值随轴重的增加而减小;建议采用φ=1+0.0045v计算墩顶动力系数,采用三角级数式拟合桥墩荷载谱效果显著。研究成果可为重载列车作用下桩基的长期承载变形性状及环境振动评估的研究提供关键参数和可靠检验样本。

Experimental research on characteristics of vertical dynamic load on bridge pier and pile foundation under heavy-haul railway train

To investigate the dynamic load characteristics of bridge pier and pile cap under heavy-haul train with large axle load, long marshalling and intensive operation, field tests on vertical dynamic load (strain) of pier and pile foundation system under different heavy-haul train load were performed. The time domain and frequency domain analysis methods were applied to study the characteristics of dynamic load curve, the Kolmogorov method was used to test the normality of dynamic load amplitude, and the relationship between train parameters and load frequency domain characteristics was established; Based on the 3σ principle, statistical analysis was performed to obtain the dynamic load characteristic values (mean value, mean amplitude value and mean peak value) under different vehicles. The calculation formula for dynamic amplification factor of pier top was proposed, and the load spectrums and their parameter values of bridge pier top and pile cap were proposed. The results indicate that the time domain response of dynamic load can be divided into three stages: rapid increase, periodic action and rapid attenuation. Moreover, the excitation frequency range of 0~5 Hz has a significant effect on dynamic load, and the spectrum curves follow the frequency multiplication rule and amplitude modulation effect. Further, it is observed that the dynamic load amplitude follows the normal distribution. The mean peak value of dynamic load and the vibration energy decrease rapidly along the pier shaft, the peak dynamic load and the mean peak value increase with the increase of the axle load, and the amplitude value may decrease with the increase of the axle load. Based on analysis results, it is suggested to apply the formula φ=1+0.0045v to calculate the dynamic amplification factor of pier top, and the load spectrum of pier can be well fitted by the trigonometric series.