中小跨径公路混凝土简支梁桥冲击系数研究及建议取值

为弥补中国现行桥梁规范中计算动力冲击系数时考虑因素单一的不足,对冲击系数的影响因素进行研究,并提出更合理的冲击系数建议值。首先,根据中国桥梁通用图集建立13座不同截面形式和不同跨径的常见中小跨径公路混凝土简支梁桥的有限元模型,结合能表征中国设计车辆荷载动力特性的三维车辆数值模型,建立车桥耦合振动分析系统。然后,基于车桥耦合振动分析系统,研究桥梁基频、桥面不平整度、车速和车质量等因素对动力冲击系数的影响,并与中国现行桥梁设计规范中的动力冲击系数取值进行对比分析。最后,提出冲击系数的建议值,并与世界各国桥梁规范中的冲击系数取值进行对比,讨论建议值的合理性。结果表明:桥面不平整度是影响冲击系数的重要因素,在桥面好的情况下,冲击系数均在0.1以下,低于规范中规定的冲击系数,而桥面很差时,冲击系数可达0.5,远大于中国现行规范中的冲击系数设计值,因此,定期对桥面进行维护能有效减小车辆对桥梁的冲击效应;质量轻的车辆引起更大的冲击系数,但由于车辆总质量轻,其导致的总荷载效应仍然较小,而重车虽然引起的冲击系数较小,但由于其导致的总荷载效应较大,更易对桥面造成损伤,因此,限制超载尤为重要。

Studying Impact Factors for Short- and Medium-span Simply Supported Concrete Highway Bridges and Its Suggested Values

Currently, only a single factor affecting the impact factor (IM) in calculations is considered in bridge design code in China. To compensate for this drawback, in this study, the factors that affect the IM were investigated and more reasonable IMs were proposed. First, the finite element models of 13 short- and medium-span simply supported concrete highway bridges with different cross-sections and spans were built based on a general atlas of bridges in China. A three-dimensional (3D) vehicle model that can represent the dynamic property of vehicle design load was adopted for vehicle loading. A 3D vehicle-bridge coupled system was then developed. With this system, the effect of four important factors-the fundamental frequency of the bridge, road surface condition (RSC), vehicle speed, and vehicle weight-on the IM were investigated. The IMs obtained from numerical simulations were compared with the IMs specified in the bridge design code. Based on the numerical results, the suggested IM values were proposed and compared with the IMs specified in the bridge design code of countries globally. In addition, the rationality of the proposed IMs was discussed. The results demonstrated the following:the RSC has a significant effect on the IM. The IM is less than 0.1 when the RSC is in a good state. However, the IM can reach 0.5, which is much greater than the IM specified in the bridge design code, when the RSC is in a very poor state. Therefore, regular maintenance of the deck can effectively reduce the impact of the vehicle on the bridge. Lighter vehicles tend to generate greater IM values, but the overall loading effect caused by light vehicles remains small. Although the IM caused by heavy vehicles is small, the overall loading effect caused by heavy vehicles is greater, which causes greater damage to the bridge deck. Therefore, limiting overload is particularly important.