Based on an analysis of random process response of a MDOF system with modal analysis method,the formulas of the related parameters for its structural dynamic reliability were derived.The PMDK dynamic reliability analysis program with Fortran programming language.Then,a solving method for parameters of a vehicular load probability distribution model was derived with a method of unconstrained planning.Combining with observation data for vehicle distribution at a long-span old bridge,the model for calculating vehicular load probability distribution was obtained.Finally,the dynamic reliability for the long-span old bridge under the actual vehiclar load was calculated with the program.The relationship between the dynamic reliability and displacement as well as the varying law of the dynamic reliability with different cross-section positions and the influences of damping and elastic modulus on the dynamic rerliability were investigated.Meanwhile,the relationship between the dynamic reliability and time and the varying law of the structural unilateral and bilateral reliabilities were also studied.The correctness of all aboved results was verified with Monte Carlo method.%基于多自由度体系随机过程分析的振型分解法,推导结构动力可靠度分析相关参数的计算公式；用Fortran语言编制PMDK动力可靠度分析程序；用无约束规划求解方法,推导车辆荷载概率分布模型参数求解方法,并结合某大跨旧桥实际车辆分布具体观测数据,获得计算概率模型.运用所编制程序计算该桥在实际车辆荷载作用下的可靠度,并研究该可靠度与位移之关系、不同截面位置动力可靠度变化规律、阻尼与弹性模量变化对大跨旧桥动力可靠度影响、时间变化影响、结构单侧及双侧可靠度变化规律等.通过蒙特卡罗法分析,验证结论的准确性.
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