| With industrial equipment imported from abroad or domestic manufactured increasingly developing in the trend of maximization and heavy industrialization, super load vehicles which transport large-sized equipments growingly frequently appear in highway industry. Super vehicle loads directly challenge carrying capacities of bridge structures. As the most common type of bridges built in domestic is reinforced concrete or prestressed concrete bridges, it is necessary to deeply research on safety of super load vehicles crossing concrete bridges.Reliability assessment method based on probability theory is a means of synthetically analysing on disease conditions, carrying capacities, safety, durability and fitness of existing bridges. This paper is supported by the science and technology project sponsored by Transportation Bureau of Guangdong Province (2010-0-16) "Reliability Method Research on Load Limit for Super Load Vehicles Crossing Concrete Bridges" By the means of reliability theory safety reliability is investigated at the background of super load vehicles crossing concrete bridges. The main research contents and results can be obtianed as follows:(1)Research status of concrete structures reliability and research results on super load vehicles are summarized. Available assessment methods of existing concrete bridges in service are compared on both of advantages and disadvantages. The basic theory as well as analysis and calculation methods of structure reliability are concluded. Failure criterion and failure modes of bridge structures and probability models of structure resistances, dead loads and super vehicle loads are researched and analyzed. And then the theoretical basis of this paper is established.(2)According to summarizing and analyzing on variabilities of wheelbases and axle loads of a super load vehicle and the one caused by pit scales, probability model of super vehicle loads is simulated by standard normal distribution in this paper, by which when load effect of the super load is unit 1, its variability is 0.0368.(3)An improved annual failure probability method is presented by which the distribution of failure probability is simulated by linear increasing by year. In order to make up the shortcoming of target reliability index approaching infinity in the initial of bridges'construction after completion, a modus of limiting the target reliability index is given.(4)Reliability indexes of bridge structures are calculated when partial coefficient of a super load vehicle is 1.00,1.02,1.04,1.06,1.08,1.10,1.12 and 1.14, and the ratio of super vehicle load effects to those of dead load is 0.1,0.2,0.4,0.6,0.8,1.0,1.5,2.0,2.5 and 3.0 respectively, by which the safety reliability discrimination formula on super load vehicles crossing concrete bridges based on reliability theory is obtained.(5)Under super vehicle load levels of 224t,287t,412t and 559t, ordinary reinforced concrete simply supported T-beam bridges with span lengths of 8m,10m,13m,15m, 18m and 20m, and simply supported or continuous T-beam prestressed concrete bridges with span lengths of 25m,30m,35m and 40m are evaluated on safety reliability. It is shown that in results of calculation and evaluation when the bridge is shorter than a super load vehicle, its load effect value is relatively little, however it significantly increases at the moment of a span exceeding length of the vehicle, and continuous beam bridges that are forced more reasonably can bear a heavier super load than simply supported ones.
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