大型储罐抗震设计计算在中美规范中的对比分析

COMPARATIVE ANALYSIS ON SEISMIC DESIGN CALCULATION OF LARGE STORAGE TANKS IN CHINESE AND AMERICAN CODES

大型储罐在地震作用下,常见的破坏形式有罐壁下部出现象足(轴压失稳)、浮动顶与固定顶发生撞击、储罐整体翘离倾覆等,为此,中美设计规范均对大型储罐的抗震设计作出了相应规定。文章结合工程案例,着重比较了锚固系数、底圈罐壁最大轴向压应力以及晃动波高在中美抗震设计计算中的差异,结果表明:对于锚固系数的计算,国内规范参考了美国规范的计算公式,但未考虑场地类别和储罐重要度系数对锚固系数的影响;对于底圈罐壁轴向压应力的计算,在锚固情况下以及锚固系数≤0.785时,国内规范表达式和美国规范类似,计算结果主要受竖向地震加速度和弯矩调整系数的影响,而在其他非锚固情况下,两者计算差异还受到翘离系数取值不同的影响;对于晃动波高的计算,国内规范考虑了罐形的影响,而美国规范则考虑了地震用途组别、储液晃动基本周期、反应谱加速度等因素的影响。

Elephant foot buckling(axial compressive instability)of the lower part of tank wall,collision between floating roof and fixed roof,and overturning of storage tank as a whole are the common damage of large storage tank under earthquake load.For this reason,corresponding provisions were made in the U.S.and Chinese design codes for seismic design of large storage tanks.Combining with engineering cases,this paper focuses on comparing the differences between the anchorage coefficient,the maximum axial compressive stress of the bottom ring tank wall and the sloshing wave height in the seismic design calculation of the U.S.and Chinese design codes.The results show that for the calculation of anchorage coefficient,the domestic code took reference from the calculation formula of the American code,but didn’t take into account the impacts of the site category and the importance factor of the storage tank on the anchorage coefficient;for the calculation of axial compressive stress in the bottom ring wall,the domestic code expressions were similar to those in the American code in the case of anchorage or when the anchorage coefficient was not more than 0.785;the calculation results were mainly affected by the vertical seismic acceleration and coefficient of moment adjustment,while in other non-anchored cases,the difference between the two calculations was also affected by the different values of the buckling coefficient;for the calculation of sloshing wave height,the domestic code took the influence of tank shape into account,while the U.S.code took the influence of seismic use groups,the basic cycle of liquid storage sloshing,and the acceleration of the reaction spectrum into consideration.