ABSTRACT
The steel box girder has replaced truss steel girder in highway long-span bridges with its advantages of the light weight, good wind-resistant stability, high torsional stiffness and convenient construction and maintenance. With the increasing of ages in services, the fatigue and corrosion problems of steel box girder have been increasingly prominent. The steel structure of bridge bears the cycle stress from vehicles and wind and if inappropriately designed and maintained, the fatigue and corrosion damage will cause the decline of plasticity and fatigue property of steel structure and accelerates the formation and extension of cracks, thus weakening the strength of steel box structure.
The fatigue fuzzy comprehensive assessment method was put forward by fuzzy mathematics for fatigue problems of the steel box girder. Membership theory and fuzzy linear transform principle were adopted to take each influencing factor into comprehensive consideration and make reliable and comprehensive assessment. Firstly, the factor set was U = {u1, u2,…, un}, each factor in which referred to properties of objects, including crack length, developing rate, corrosion level, fatigue level and service time of bridges. Secondly, each element uiin factor set was assessed by single factor. The fuzzy statistical method, paired comparison and expert experience method were adopted to establish steel box fatigue comprehensive assessment function, namely, Ri = (ri1, ri2, …, rin). Lastly, cjwas set beforehand for each evaluation grade vj in V = {v1, v2, …, vm}. The weighted average method was adopted to obtain const C, taking the power of membership bj in B as weight.
The corrosion damage comprehensive score system of steel box girder was put forward on the basis of current assessment methods for the corrosion problems of the steel box girder. Add two new judgement indexes, corrosion depth percentage and corrosion location, to the current assessment indexes. The corrosion indexes corresponding to each kind of corrosion types were selected according to the current corrosion indexes, combined with the features of steel box girder and corrosion types. The limit value of each index was also presented. The corresponding values and grades were identified through certain measure methods after the specific corrosion indexes were confirmed required by steel box girder corrosion judgement. The grade of each index was added and the corresponding corrosion amplification coefficient was multiplied. Lastly, the corrosion level of a certain part was judged, which could be the theoretical support for daily inspection and maintenance in terms of different corrosion levels of steel box girder. The fatigue fuzzy comprehensive assessment method. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig279_1.tif"/>
The assessment examples of different corrosion types were also given according to the comprehensive score system put forward in this paper.
