平底円筒タンクの底板浮上がり挙動に関する一考察

有限要素法による動的非線形解析

抄録

Oil storage tanks are usually constructed directly on the earth foundations without anchors. In such a flat-bottom cylindrical tank subject to seismic excitaion, a part of the bottom plate adjacent to the shell will be lifted off the foundation due to overturning moment and it results in a failure of the shell-to-bottom junction. R. S. Wozniak and others treated the uplifted bottom plate as an elemental strip based on small deflection theory and assumed the development of two plastic hinges. Their investigations were summarized into API Standard 650 Appendix E as the seismic design provisions. But the nonlinear dynamic characteristics of this phenomenon are not yet clear.
In this paper, calculations are carried out for a 9500kl oil storage tank under various conditions by the finite element code “CNCL-ND” developed by the author, and numerical results show dynamic effects on the uplifting behavior of tank bottom.
As a result, it was found that the nonlinear relation exists between uplift height and uplift width of annular plate independently of excitation and it is also in good agreement with Wozniak's method. Furthermore, the ultimate strength of annular plate evaluated by Wozniak shows some conservative value in comparison with calculation results by FEM.