| In the recent years of practical engineering indicates in-service steel structure suffered the atmospheric corrosion can not be ignored with the aggravating global climate. It is not only caused to reduce the cross-section, but also caused to steel yield strength, ultimate strength, yiele ratio, elongation and other mechanical changes in performance indicators, which has seriously affected the reliability of steel structures. Steel structure durability is one of the world-wide concerned problems in the field of the structure engineering. Combining with the National Natural Science Foundation of China, test studies combined with theoretical analyses are used to correlative investigation on stiffness and stability problem of the corroded steel beam.This paper will study the corroded steel structure in natural atmospheric conditions and test materials are from the practical engineering. Firstly, considering the corrosion depth, the shape and the density have great randomness, this paper measure the four representation status of pit corrosion with the roughness instrumentation and receive the statistics of corrosion depth in local surface. Applying the probabilistic method, the deepest depth of corrosion are obedient to Gumbel first kind of probability distribution rule. Secondly, according to the random field theory, the stationarity and ergodicity of corroded section are examed, which should be the basic principle of the random theory. After this, a theoretical random field modol is established for corroded section base on a large number of investigation data. On the basis of the random field model, corroded steel structure the flexural stiffness and stability capacity degradation model are presented in this paper. The conclusions of this paper not only provide the decision-making for the security control and reinforcement of steel structure engineering in-service corrosion, but also provide a reference for establishing the stochastic finite element model.
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