Evaluation of Residual Strength of Offshore Structures

通过一系列的倒塌试验和壳体有限元分析，研究了海洋结构经历凹陷损伤、整体弯曲损伤和裂纹损伤后的剩余强度。在此基础上，对现有的理想结构单元法(ISUM)的损伤管件模型进行了改进，通过弯曲屈曲试验和有限元分析发现，在压痕过程中会产生较大的残余应力，从而导致压痕区域受拉时构件的刚度大大降低。当凹陷区在压缩荷载作用下受力时，承载能力大部分降低，而在拉伸荷载作用下，由于凹陷深度的减小，承载能力可以恢复到完整构件的极限强度。然而，与完好的状态相比，变形和局部应变都很大。对ISUM进行了改进，以考虑拉伸凹陷损伤情况下刚度的降低和凹坑深度的变化，并通过与试验结果和FEN结果的比较验证了该方法的有效性。对含周向槽厚裂纹的管状试件进行了弯曲坍塌试验、拉伸坍塌试验和相关的有限元壳体分析。对已有的裂纹管杆件ISUM进行了改进，使其可以在刚度计算中考虑裂纹尖端局部屈服的影响。利用改进的ISUM对平面框架和空间刚架等几个有损伤的算例进行了分析，研究了损伤对结构承载能力的影响。

Residual strength of offshore structures which experienced denting damages, overall bending damages and cracked damages was investigated through a series of collapse tests and FEM shell analyzes on damaged tubular members. Based on the results, several improvements were made on the existing models of the Idealized Structural Unit Method (ISUM) for damaged tubular members.From the bending collapse tests and FEM analyzes on tubular specimens with denting damages, it has been found that a significant magnitude of residual stress is induced during indenting process and this results in a large reduction of member stiffness when dented region is loaded in tension. When the dented region is loaded in compression, a load carrying capacity is mostly reduced, while in tension it may be recovered up to the ultimate strength of intact members because of the decrease of dent depth under the action of tensile load. However, deformations and local strains are large compared to the intact condition. The ISUM was improved so as to consider the reduction of stiffness and the change in dent depth for the case of dented damage loaded in tension, and the validity was demonstrated through a comparison with tested and FEN results.Bending collapse tests, tensile collapse tests and the related FEM shell analyzes were performed on tubular specimens with a circumferential trough-thickness crack. The existing ISUM for cracked tubular members were also improved so that the effect of local yielding at crack tip can be considered in stiffness calculation.Using the improved ISUM,several examples including plane frames and space frames having damages were analyzed and the effects of damaged on the load-carrying capacity of structures were investigated.