Temporary Tank Footing Design Based on ACI 318-14
There are several types of tanks, e.g., above-ground, flat-bottomed, cylindrical tanks for the storage of refrigerated liquefied gases, petroleum, etc., steel or concrete silos for the storage of coke, coal, grains, etc., steel, aluminium, concrete or FRP tanks including elevated tanks for the storage of water, spherical tanks (pressure vessels) for the storage of high pressure liquefied gases, and under-ground tanks for the storage of water and oil. The trend in recent years is for larger tanks, and as such the seismic design for these larger storage tanks has become more important in terms of safety and the environmental impact on society as a whole. The failure mode of the storage tank subjected to a seismic force varies in each structural type, with the structural characteristic coefficient (Ds) being derived from the relationship between the failure mode and the seismic energy transferred to, and accumulated in the structure. A cylindrical steel tank is the most common form of storage tank and its normal failure mode is a buckling of the cylindrical shell, either in the so called Elephant Foot Bulge (EFB), or as Diamond Pattern Buckling (DPB). The Ds value was originally calculated with reference to experimental data obtained from cylindrical shell buckling, but was later re-assessed and modified based on the restoring force characteristics of the structure after buckling. Those phenomena at the Hanshin-Awaji Great Earthquake and the Niigataken Chuetu-oki Earthquake were the live data to let us review the Ds value. For the EFB, which is the typical buckling mode of a cylindrical shell storage tank for petroleum, liquefied hydrocarbon gases, etc., it became possible to ascertain the buckling strength by experiments on a cylindrical shell by applying an internal hydrodynamic pressure, an axial compressive force, and a shear force simultaneously
Design recommendation for sloshing phenomena in tanks has been added in this publication. Design spectra for sloshing, spectra for long period range in other words, damping ratios for the sloshing phenomena and pressures by the sloshing on the tank roof have been presented. For above-ground vertical cylindrical storage tanks without any restraining element, such as anchor bolts or straps, to prevent any overturning moment, only the bending resistance due to the uplift of the rim of bottom plate exists. This recommendation shows how to evaluate the energy absorption value given by plasticity of the uplifted bottom plate for unanchored tanks, as well as the Ds value of an anchored cylindrical steel-wall tank. As the number of smaller under-ground tanks used for the storage of water and fuel is increasing in Japan, the Sub-committee has added them in the scope of the recommendation and provided a framework for the seismic design of under-ground tanks. The recommendation has accordingly included a new response displacement method and a new earth pressure calculation method, taking into account the design methods adopted by the civil engineering fraternity.
Design recommendation for sloshing phenomena in tanks has been added in this publication. Design spectra for sloshing, spectra for long period range in other words, damping ratios for the sloshing phenomena and pressures by the sloshing on the tank roof have been presented. For above-ground vertical cylindrical storage tanks without any restraining element, such as anchor bolts or straps, to prevent any overturning moment, only the bending resistance due to the uplift of the rim of bottom plate exists. This recommendation shows how to evaluate the energy absorption value given by plasticity of the uplifted bottom plate for unanchored tanks, as well as the Ds value of an anchored cylindrical steel-wall tank. As the number of smaller under-ground tanks used for the storage of water and fuel is increasing in Japan, the Sub-committee has added them in the scope of the recommendation and provided a framework for the seismic design of under-ground tanks. The recommendation has accordingly included a new response displacement method and a new earth pressure calculation method, taking into account the design methods adopted by the civil engineering fraternity.
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