The membrane stress in the roof plate (which is not attached to the rafter) resists the uplift force.

The rafter system does not resist the uplift. RE: Uplift In Storage Tank Foundation fahedjavaid (Structural) If you hold the capacity and make the tank taller and narrower, uplift problems will be reduced. Using an inverted-T foundation will allow you to use soil weight instead of just concrete weight. One thing to note on foundation sizing is that as you extend a ringwall inside the shell, the tank design pressure is also acting down on that part of the ringwall, which will offset some of the uplift. The tank and foundation could likely be built for that pressure, it would just be very expensive. Note that the test pressure and failure pressure must also be considered as a design case, and may control rather than the design pressure. For larger tanks, you come up with unreasonable amounts of top angle area required, unreasonable anchorage, and unreasonable foundation sizes.

For smaller tanks, the uplift is manageable, and may result in a larger ringwall. In most cases, when a too-high pressure is specified for a tank, they are able to reduce that pressure once they realize it has a major impact on the tank and foundation design (and cost).ĪPI-650 includes allowances for pressures up to 2.5 psi, which is what is used here. You need to contact the tank designer and tank specifier and let them know what is going on. The problem is that it is an unreasonable pressure for that size of tank.

Impact force of a tank shell