Effects of Crack Damages on the Structural Response of Offshore Structures

1.对海洋结构物的裂纹损伤进行了调查。结果表明，裂纹损伤最有可能发生在管状接头处，碰撞或物体坠落造成的凹陷损伤起到了裂纹启动者的作用，因为齿底部有很大的应变集中。对含周向穿透裂纹的管状构件进行了一系列纯拉、纯弯曲试验。考虑延性裂缝扩展的影响，对含裂纹钢管构件的刚度和承载能力进行了研究。在实验结果的基础上，用有限元方法进行了生成相分析。结果表明，CTOD和CTOA分别是影响裂纹萌生和扩展的断裂参数。基于半膜壳理论和Dugdale模型的假设，推导了估算CTOD和CTOA的理论公式。提出了一种考虑延性裂纹扩展的环向穿透裂纹管构件的理想结构单元法。在弹性分析中，在两个完整的梁柱单元之间插入一个裂纹弹簧单元，而在基于塑性节点法的弹塑性分析中，则插入一个塑性铰。算例包括含裂纹损伤的超静定门式刚架，验证了该方法的准确性和有效性。

1. A survey of the crack damages of offshore structures was made. It was shown that the crack damages were most likely to take place at the tubular joints and that the dented damages caused by collisions or object fallings acted as a crack initiator because of a large strain concentration at the bottom of the dent.2. A series of pure tensile and pure bending tests of a tubular member having a circumferential through-thickness crack was carried out. The rigidity and load carrying capacity of the cracked tubular members were investigated considering the effects of ductile crack growth.3. Based on the experimental results, the generation phase analysis was performed with the finite element method. It was found that CTOD and CTOA were the fracture parameters effective for the crack growth initiation and continuation, respectively.4. The theoretical formula for the estimation of CTOD and CTOA were derived based on the semi-membrane shell theory and the assumption of Dugdale model.5. The idealized structural unit method for a circumferentially through-thickness cracked tubular member was newly developed considering the ductile crack growth. A crack spring element was inserted between two intact beam-column elements in elastic analysis, while a plastic hinge was inserted in elastoplastic analysis based on the plastic node method.6. Several numerical examples including a statically indeterminate portal frame with a crack damage showed the accurate and efficient capability of the proposed method.