考虑激励、构件和响应因素异型拱桥冲击系数研究

Study on impact coefficient of special-shaped arch bridge considering excitation,member and response

为了计算相对较柔、自振频率较低的异型拱桥结构的车辆冲击系数,以某多拱肋宽幅异型钢管混凝土拱桥为依托,探讨现行规范冲击系数取值的适用性,探究依托拱桥设计时的统一冲击系数。考虑车速、车辆数、车队间距和车辆偏载等不同加载因素,分析对不同构件和不同响应冲击系数的影响。在此基础上,基于包络回归分析,分别选择线性、2次、3次函数对应的包络曲线,对比给出该桥的主拱挠度、弯矩冲击系数与车速之间的回归公式。最后,对比冲击系数拟合曲线与规范值的偏差。研究结果表明:对于异型钢管混凝土拱桥这一类构造复杂且频率相对较低的柔性结构,不同活载激励、不同构件、同一构件不同位置、不同响应的冲击系数均存在差异,部分冲击系数超出现行国家规范,全桥选用统一冲击系数可能产生较大偏差。车辆行驶速度对活载冲击系数影响较大。相比于现行规范冲击系数,回归公式计算挠度、弯矩冲击系数包络效果较好,挠度、弯矩冲击系数与车速间回归公式有一定安全富余,可分别用来计算桥梁结构的挠度和弯矩的冲击系数。

In order to calculate the impact coefficient of arelatively flexible bridge structure with low natural frequency,a wide and special-shaped concrete-filled steel tubular arch bridge with multiple arch ribswas taken as an exampleto explorethe applicability of the calculated value of impact coefficient in the current codeand to investigatethe rationality of taking a unified impact coefficient in the design of an arch bridge.Then,different loading factors such as speed,number of vehicles,fleet spacingand vehicle partial loadwere considered to analyzethe effects on the impact coefficients of different members and different responses.On this basis,based on envelope regression analysis,the envelope curves corresponding to linear,quadratic and cubic functions were compared to givethe regression formulas between main arch deflection,moment impact coefficients and vehicle speeds.Finally,the deviationsof the fitted curves of impact coefficients from the standard values was compared.The results show that for the flexible structure with complex configurationand relatively low frequency,the impact coefficients of different live load excitation,different components,different positions of the same component and different responses are different.Some impact coefficients exceed the value got from the Chinese codeand employing one unified impact coefficient for the whole bridge may producea large deviation.Vehicle speed has a great influence on the live load impact coefficient.Compared with the impact coefficient in the current code,the envelope effect of deflection and bending moment impact coefficient calculated by the regression formula is better.The regression formulas between deflection,moment impact coefficient and vehicle speed have a certain safety margin and can be used to calculate the deflection and moment impact coefficient of bridge structure respectively.