Evaluation of Residual Strength of Offshore Structures

通过对钢管构件进行一系列的破坏试验和有限元壳分析，研究了海上结构在遭受凹陷损伤、整体弯曲损伤和裂纹损伤时的剩余强度。在此基础上，对现有的管状构件理想结构单元法（ISUM）模型进行了改进。通过对具有凹痕损伤的管状试件的弯曲破坏试验和有限元分析，发现在凹痕过程中会产生相当大的残余应力，从而导致构件在凹痕区受拉加载时刚度的大幅度降低。凹痕区域在压缩荷载作用下，承载能力大部分下降，而在拉伸荷载作用下，由于凹痕深度的减小，承载能力可能会恢复到完整构件的极限强度。然而，与完整状态相比，变形和局部应变较大。针对拉伸载荷下凹痕损伤的情况，对ISUM进行了改进，考虑了刚度的降低和凹痕深度的变化，并与试验结果和FEN结果进行了对比，验证了ISUM的有效性。对带周向槽厚裂纹的管状试件进行了弯曲破坏试验、拉伸破坏试验及相应的有限元壳层分析。改进了现有的管状开裂构件的ISUM，以便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方法，分析了平面框架和空间框架的损伤情况，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.