Utilization of Subjective Information to the Problem of Structural Maintenance

船舶结构的在役检测对保证结构的疲劳损伤安全起着重要的作用。然而，在进行合理的检验时，除了需要明确构件的可靠性水平外，还需要明确构件的现有可靠性水平，从这一角度出发，对散货船6个构件进行了重复检验下的疲劳可靠性分析。构件的裂纹产生和扩展特性、通过目视检查的裂纹检测概率、构件的目标失效概率等，通过对船舶工程师的问卷调查，收集了可靠性分析中的重要信息，并利用问卷调查结果进行了疲劳可靠性分析和敏感性分析。为此，采用马尔可夫链模型，将裂纹长度超过200 mm或500 mm定义为失效事件。通过计算，在目前的条件下，对疲劳可靠性的重复检查的效果，以及所需的检查间隔，以达到目标的失效概率为六个成员进行了调查。主要结论如下：（1）通过问卷调查获得了散货船六个部位的疲劳特性和POD曲线。(2)如果采用间隔两年的ISI，则在20年期间至少有60%至70%的初始裂纹被ISI检测到。(3)间隔2年的ISI可使不检查时的失效概率Pf（200）降低到1/3，使Pf（500）降低到1/5。(4)实现目标Pf（200）需要6个月的检查间隔，实现目标Pf（500）需要1.5年。(5)针对提高可靠性、减轻重量、简化检测等设计要求，提出了相应的解决方案。

In-service inspection on ship structure plays an important role for maintaining safety against fatigue damage. However, when we want to perform reasonable inspection, it is necessary to clarify the present reliability level of structural members as well as the desirable level.From this point of view, fatigue reliability analysis under repeated inspections is carried out for the six structural members of bulk carrier. Crack initiation and propagation properties of the members, probability of crack detection by the visual inspection, target failure probabilities of the members and etc., which are essential information in the reliability analysis, are collected by the questionnaire asked to the navel engineers.Then fatigue reliability analysis and sensitivity analysis are carried out using the questionnaire results. Markov Chain Model is employed for this purpose, in which crack length exceeding 200mm or 500mm was defined as the failure event. Through the calculations, effect of repeated inspections at the present condition on fatigue reliability, and the inspection intervals necessary to achieve the target failure probability are investigated for the six members. The major conclusions are drawn as follows :(1) Fatigue characteristics and POD curves by visual inspection were obtained for the six locations of bulk carrier by the questionnaire.(2) If ISI of two years interval is applied, al least 60 to 70% of initiated cracks are detected by the ISI during 20 years.(3) ISI of two years interval can reduce the failure probability Pf (200) under no inspection to 1/3 and the Pf (500) to 1/5, respectively.(4) Inspection interval of 6 months is necessary for the achievement of target Pf (200) and 1.5 years for target Pf (500).(5) For the design requirements such as the improvement of reliability, reduction of weight and simplification of inspection, the solutions to respond to the requirements were extracted.