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Unitized Systems - Engineering Page 3 of 4 <br /> resist overturning. <br /> TANK <br /> It should be further noted there is no need for Tank tie-downs to <br /> deadman buried in the surrounding soil to resist overturning of the <br /> PetroFirst Tank. Tie downs are not required for any reason other <br /> than to resist the tendency to float as it is with any U.G. tank <br /> installation. <br /> V. Buoyancy: The uplift analysis assumed a worst case scenario <br /> of an empty Tank completely submerged. The overburden, drive <br /> slab and canopy structure are in place and the unit is <br /> simultaneously subjected to uplift forces of 110 mph. hurricane <br /> winds. The calculations clearly identify there is no need for tie- <br /> down to deadman in the surrounding soil once the Tank <br /> installation is fully complete as described above. <br /> CAUTION: The critical time for potential Tank floating is during <br /> the construction process. PetroFirst recommends all tank <br /> installations should be fully ballasted and tied-down to deadman <br /> to preclude any potential for floating particularly in geographical <br /> areas with high water tables and/or areas subject to heavy rainfall <br /> conditions. <br /> VI. Fatigue Analysis: The fatigue stress analysis focused on the <br /> most critical point on the Tank base metal at the toe of the fillet <br /> welds adjacent to the column connection seat. The analysis used <br /> the AISC, category "C" specifications which prescribes a large <br /> number of loading cycles (2,000,000) at a design wind velocity of <br /> 110 mph. The analysis identifies that fatigue stress is of no <br /> concern whatsoever. The analysis produced a margin of safety <br /> regarding fatigue stress of 560 percent with the canopy connection <br /> being subjected to 110 mph hurricane winds, 183 times per year <br /> for 30 years. <br /> VII. Seismic Load Analysis: In earthquake conditions the U.G. <br /> PetroFirst Tank must resist the dynamic loading from the <br /> movement of the surrounding earth. One must remember the Tank <br /> is a monolithic steel structure internally stiffened at several points <br /> along the length of the tank and further reinforced by the <br /> application of the steel trough welded longitudinally along the top <br /> length of the tanks as well. Steel tanks are inherently more <br /> resistant to damage due to earthquakes than tank or other materials <br /> (such as fiberglass) and in the case of PetroFirst the added <br /> structural integrity further decreases the likelihood of failure <br /> http://Www.plasteel.com/pfeng.html 8/28/2003 <br />