结构自振周期较大的浅水平台应进行详细疲劳分析

The detailed fatigue analysis to shallow water platform structures

浅水水域的平台一般不会出现管节点疲劳问题 ,在一定条件下可以用简化疲劳分析替代详细疲劳分析 ,平台结构设计规范APIRP 2A对此也有相应的规定。但在对某些自振周期较大的浅水平台进行详细疲劳分析时发现 ,当平台完全符合进行简化疲劳分析条件时 ,个别管节点的疲劳使用期限低于设计要求。由此 ,对浅水平台结构为什么出现疲劳问题进行了探讨 ,并从平台的设计工作水深、自振周期、简化疲劳分析条件和波浪出现概率等方面 ,对某些浅水平台结构具有相对较大自振周期的情况进行了详细分析。若浅水平台结构的自振周期较大、接近于小波浪周期 ,且平台工作在小波浪出现的密集区 ,则容易出现平台结构自振周期接近共振周期的状况 ,使平台结构具有动力响应 ,产生动力放大 ,并引发管节点发生破坏。因此 ,设计此类平台结构时 ,不能用简化疲劳分析方法 ,而要进行详细疲劳分析。

Commonly, no joint fatigue problems occur on the shallow water platforms, so that the simplified fatigue analysis can be used instead of detailed fatigue analysis under certain conditions and also there are corresponding provisions in API RP 2A the recommended practices for design of platform structures. However, according to the results of detailed fatigue analysis to shallow water platforms with relatively large natural period, it is found that the fatigue life of few joints is less than designed requirements when the platforms satisfied the simplified fatigue analysis conditions. Therefore, the reasons why fatigue problems accrued on the shallow water platforms have been invested and the relatively large natural period on some shallow water platforms have been analyzed in detail in the respects of designed water depth, natural period, simplified fatigue analysis conditions and occurrence probability of waves. If shallow water platform structure has relatively great natural period close to small wave period and works in small wave-concentrated area, the natural period is close to resonant period easily, resulting in the dynamic response and dynamic amplification and the failure of joints of the structure. Therefore, detailed fatigue analysis must be done during the design of such platform.