Abstract
It is very important in safety design of oil storage tanks to prevent their bottom plates from corrosion and to ensure them against earthquake damage. When a violent earthquake occurs, a part of the shell plate of unanchored cylindrical oil storage tanks will be lifted from their foundations due to overturning moment, and local strain of annular bottom plate near the shell to annular joint will increase. As the result, damage such as cracks of coating material on annular plate may be caused. This paper deals the uplift behavior of tanks due to earthquake.
In order to evaluate quantitatively the uplift displacement of shell lower edge of 110000m3 oil storage tanks by earthquakes, nonlinear time history analyses were carried out by using mechanical model of mass-spring system, where non-linearity associated with the partial uplift of shell plate is considered as rotational spring of a bilinear type. The analytical results show that EW direction wave of “Far off Sanriku earthquake (1994)” (with maximum acceleration 293gal) causes the maximum uplift about 5cm at shell lower edge. The critical value of shell uplift prescribed in evaluation of “existing horizontal load bearing capacity” of tanks by current Fire Service Law is regarded as about 21cm. Therefore the calculated uplift value of 5cm is lower than the critical value.
