交通量持续增长下大跨桥梁时变极值外推分析

随着交通运输行业的迅速发展，持续增长的交通荷载逐步成为威胁既有桥梁运营安全的重要因素。为了研究现有交通荷载持续增长对大跨桥梁安全水平的影响，提出考虑交通量区间增长的车载效应极值外推方法，采用基于"时间离散"和"极值概率串联"的改进Rice公式捕捉交通量持续增长导致极值概率的时变特征，由两个数值算例验证考虑交通量增长的时变极值外推的精确性。基于某高速公路实测车流数据模拟了随机车流，预测了车流量线性增长下悬索桥运营期内的最大位移。研究结果表明:交通量增长导致荷载极值时变特征显著，基于独立同分布假定的经典极值理论与Rice公式均无法准确地对拟合高尾极值，而改进Rice公式可精准拟合并外推极值；在交通量年增长系数为1%~3%时，某悬索桥设计基准期内的车载效应放大系数为1.30~1.98；若交通量年增长系数大于3%，则该桥梁1000年重现期的最大位移将大于设计标准值。

EXTRAPOLATION OF TIME-VARIANT EXTREME EFFECT ON LONG-SPAN BRIDGE CONSIDERING STEADILY GROWING TRAFFIC VOLUME

As the rapid development of the transportation industry, the steadily growing traffic load is gradually becoming a significant factor impacting the service safety of existing bridges. To investigate the influence of the actual traffic growth on the safety of long-span bridges, a methodology was presented for extrapolation of traffic load effect on long-span bridges considering an interval growing traffic model. An advanced Rice formula was developed considering a ‘time-disperses’ and ‘probability-in-series’ model to capture the time-variant characteristics of extreme traffic load due to traffic volume growth. Two verification examples demonstrated the accuracy and effectiveness of the proposed method in capturing the extrapolation of time-variant probabilities. Stochastic traffic load models were simulated based on monitored traffic load data. The maximum deflection of a suspension bridge was evaluated accounting for traffic volume growth in the bridge lifetime. The numerical results show that the time-variant characteristic of the extreme effect due to traffic volume growth is significant. The typical extreme value theory and the Rice's formula based on the assumption of independent and identically distribution are poor in capturing the tail data of the extreme value. However, the advanced Rice's formula is able to fit and extrapolate the extreme value. When the annual traffic volume growth ratio is in the range between 1% and 3%, the amplification factors of the extrapolated deflection of a suspension bridge in lifetime are in the range between 1.30 and 1.98. If the annual traffic volume growth ratio is greater than 3%, the maximum deflection in a return period of 1000 years of the bridge will be greater than the standard design value.