Practical Method of Reliability-based Assessment and Design of a Structure with Long Service Life

由于其数量巨大，延长由普通结构工程师设计的建筑结构的使用寿命是实现社会可持续发展的最重要因素之一。然而，在目前的设计规定中，并没有明确考虑结构的使用寿命。在基于可靠性的极限状态设计中，考虑使用年限以及荷载强度和结构能力的变异性，可以通过区分荷载和抗力系数来控制结构的性能水平。AIJ在《建筑极限状态设计建议》中提出了一种实用的荷载和抗力系数计算方法。然而，由于非对数正态随机变量对对数正态分布的简单逼近，参考周期固定为50年，因此，该建议不能用于设计使用寿命更长的结构，并且结构可能会因环境应力和重复加载而劣化。对于使用寿命短的结构，这种劣化可能不是问题，但对于使用寿命较长的结构，应该考虑这种劣化。然而，现有的设计规范也没有考虑结构在使用寿命期间的性能退化，对于结构性能的退化，研究者引入了抗力系数的概念，用它可以将时间相关的可靠性问题近似为时间无关的问题。根据极值分布母体分布的分类，提出了一种实用的阻力折减系数公式。同时，直接利用AFOSM提出了一种能考虑结构使用寿命的荷载和抗力系数的改进的简单逼近方法。通过数值算例研究了该方法的精度和适用性。

Because of their enormous numbers, extending the service life of building structures designed by an ordinary structural engineer is one of the most important factors for achieving sustainable society. However, the length of service life of a structure is not considered explicitly in current design provisions. In reliability-based limit state design, the performance level of a structure can be controlled by differentiating load and resistance factors considering the length of service and the variability in load intensity and structural capacity. A practical method for evaluating load and resistance factors is proposed in "Recommendation for Limit State Design of Buildings" by AIJ. However, because of the simple approximation of non-lognormal random variables to lognormal, the reference period is fixed as 50 years, and accordingly, the recommendation cannot be properly used for designing a structure with longer service life.Also a structure could deteriorate due to environmental stressors and repeated loading. Such deterioration may not be a problem for a structure with short service live, but should be considered for a structure with long service life. However, again no existing design code considers the deterioration of a structural performance during its service life.For the degradation of structural performance, the investigator has introduced the concept of a resistance factor with which a time-dependent reliability problem can be approximated as a time-independent one. In this research, a practical formula for a resistance reduction factor is proposed classifying the cumulative distribution functions according to the classification of parent distributions of extreme value distributions. Also, an improved simple approximation method, which can consider the service life of a structure, for load and resistance factors is proposed using AFOSM directly. The accuracy and its applicability are investigated using numerical examples.