Inner corrosion defects can severely impact the reliability of the corroded pipeline. The mechanical behavior and failure pressure of the pipeline with single inner corrosion defect, multiple interacting inner corrosion defects and multilayer structural inner corrosion defect were investigated by nonlinear finite element method in this paper. Effects of length, width and depth of the corrosion defect and inner pressure were discussed. The results demonstrate that von Mises stress and the plastic strain of the corroded pipeline increase with the increasing of inner pressure. Failure pressure of the corroded pipeline decreases with the increasing of length and depth of the corrosion defect, but width has a small effect on it. The pipelines with multiple and multilayer corrosion defects were also studied. Stress concentration appears on the longitudinal separation of the interacting corrosion defects. Failure pressure of the pipeline with multiple inner defects is lower than it with single inner pressure. Stress concentration and plastic deformation firstly occurs on the lowest layer of the corrosion defects and then expands to other layers with the increasing of the inner pressure.

This paper presents a new type of composite slim floor beam, determined by combining the results of an experimental study and theoretical analysis of the ultimate flexural strength of slim floor beams. The shear connectors play a significant role in the mechanical properties of this type of composite slim floor beam, because the precast concrete slab is laid on the bottom flange of the steel section and because the upper portion of the steel beam is encased in the cast-in-place concrete slab. To investigate the ultimate flexural strength, three specimens, which included headed studs, transverse steel bar shear connectors and no shear connectors, were tested. Additionally, a detailed numerical analysis was performed to verify the experimental results, which indicated that a higher-strength steel beam and thicker concrete slab can effectively enhance the stiffness and flexural capacity of the composite slim floor beam. Based on plastic mechanics and limit analysis theory, a calculation method was derived to estimate the ultimate flexural strength of a composite slim floor beam, and a comparison between the calculation and experimental results shows that the theoretical results exhibit good agreement with the experimental results, and the proposed analysis method can be used in future studies to gain a better understanding of the ultimate flexural strength of composite slim floor beams.

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