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摘要: 以公路简支梁桥为研究对象, 采用四自由度的二分之一车辆模型, 建立了车桥耦合振动方程, 计算了不同车速下桥梁跨中截面的动挠度和应变时程曲线。对比了传统定义法、试验测试法、现行规范法的冲击系数计算值, 对前2种方法进行了修正, 获得了桥梁结构的最大动效应值, 并根据主梁的最大活载内力计算原理, 引入数值加权的概念对前2种方法进行了加权计算。分析结果表明: 传统定义法和试验测试法计算的冲击系数值比《公路桥涵设计通用规范》 (JTG D60—2004) 计算值小; 由时程曲线上最大动效应处得到的冲击系数平均值约是前2种方法计算值的2倍, 且其最大值比规范法计算值小37%;基于传统定义法的挠度冲击系数值大于应变冲击系数值, 而试验测试法得到的挠度冲击系数值普遍小于应变冲击系数值; 基于传统定义法和加权法的挠度冲击系数计算值比规范值大16%;试验测试法和加权法相结合的冲击系数计算方法考虑了移动荷载对整个桥梁冲击的历程效应, 计算比较稳定。Abstract: A simply supported beam highway bridge was taken as an example, the half vehicle model with four-degree-of-freedom was employed to set up vehicle-bridge coupled vibration function, and the time-history curves of dynamic deflection and strain at mid-span under different vehicle velocities were calculated.The impact factors (IM) calculated by traditional definition method, experiment method and current code provisions were compared, the first two methods were revised to reflect the maximum dynamic response of bridge.According to the calculation principle of the maximum internal force for girder under moving load, the weighted method was utilized to replenish the first two methods.Analysis result shows that the IMs calculated by traditional definition and experiment methods are less than those in General Code for Design of Highway Bridges and Culverts (JTG D60—2004).The average value of IMs obtained at the maximum dynamic response of time-history curves doubles the first two methods, and its maximum IM is 37%less than code provision.Deflection IMs calculated by traditional definition method are greater than strain IMs, but deflection IMs calculated by experiment method are mostly less than strain IMs.The IM calculated by traditional definition method and weighted method is 16% greater than code provision.The weighted method combining with experiment method reflects the whole impact course of bridge caused by moving load, and it is stable when calculating IM.
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Key words:
- bridge engineering /
- impact factor /
- vehicle-bridge coupled vibration /
- weighted method /
- deflection /
- bending moment
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图 1 移动荷载下简支梁跨中挠度(应变) 曲线
Figure 1. Deflection (strain) curves at mid-span of simply supported beam under moving load
图 2 四自由度二分之一车辆分析模型
Figure 2. Analytical model of half vehicle with four-degree-of-freedom
图 3 简支梁跨中挠度和应变曲线
Figure 3. Deflection and strain curves at mid-span of simply supported beam
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