设计寿命是指产品设计时的预计不失去使用功能的有效使用时间，从而在理论上保证产品使用的时间长久性。
misc. projected lifetime
So the conclusion that it can not appear fatigue cracks during design life period with normal periodic maintenance is provided.
从而得出节点连接结构在正常养护维修情况下,设计寿命期内不会发生疲劳开裂的结论。
参考来源 - 大跨度钢桁桥节点疲劳性能试验与研究·2,447,543篇论文数据，部分数据来源于NoteExpress
这些节约量是从建筑结构本身的设计单独产生，在其整整40年设计寿命里不再需要替换或改变。
These savings arise solely from the design of the building fabric itself which should not require replacement or alteration during the whole of its expected 40-year life.
由波音707改装的KC - 135，是在艾森豪·威尔当政时服役的，(服役时间)已经接近设计寿命。
The KC-135, a cousin of the Boeing 707, entered service in the Eisenhower era and is near the end of its design life.
由于种种原因，许多建筑物在其设计寿命来临之前，就已经不能满足设计时所要求的各项预定功能。
Owing to all kinds of reasons, many buildings cant satisfy the desired functional requirements in design before they reach their design life expectancy.
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