美国公路桥梁设计规范中关于设计汽车荷载的研究

美国公路桥梁设计规范(AASHTO LRFD)中设计汽车荷载种类多样且复杂,介绍该规范中关于HL-93设计汽车荷载的相关规定,以及荷载影响线的动态规划法分析原理,进而研究变轴距、变车距等形式的HL-93设计汽车荷载在MIDAS Civil通用有限元软件中的快速实现方法。对国外某实桥进行HL-93设计汽车荷载效应分析,并与中国规范做对比分析。结果表明:对该多跨等截面连续梁,随着轴距的增加,主梁支点负弯矩、跨中正弯矩逐渐减小;而随着车距的增加,跨中正弯矩基本不变,支点负弯矩呈现先增大而后逐渐减小的规律。中国公路Ⅰ级与美国HL-93设计汽车荷载效应相比,主梁剪力与跨中正弯矩前者比后者大,支点负弯矩前者比后者小15%左右。

Study of Design Truck Load in AASHTO LRFD Bridge Design Specifications

The categories of design truck loads in the AASHTO LRFD Bridge Design Specifications are varied and complex.In this paper,the relevant provisions on the truck load HL-93 in the specifications and the analysis philosophy of dynamic programming method for influential lines of the load are presented and in a further step,the method for rapid executing of the load HL-93 of variable axle spacing and variable truck spacing types in the general finite element software MIDAS Civil is studied.The effect of the HL-93 of a foreign bridge is analyzed and the analysis is compared to that based on the Chinese highway code.The results of the analysis and comparison show that for the multi-span constant section continuous main beam,the negative moment at the supports and the positive moment at the midspan of the beam gradually decrease with the increase of the axle spacing,however,with the increase of the truck spacing,the positive moment at the midspan basically remains unchanged and the negative moment at the supports firstly increases and then gradually decreases.In comparison of the Class I Load in the Chinese highway code to the effect of the HL-93,the shear force and the positive moment at the midspan of the main beam of the former is greater than those of the latter while the negative moment at the supports of the former is about 15% less than that of the latter.