Tanks, Propane
In order to select the suitable type and number of anchors, we must first calculate the expected forces that the wind may apply to the tank. A fast and easy way to estimate the forces is to use our Shed Calculator. While the calculator is designed to calculate the force on a rectangular structure, using this calculator for the rounded tanks will cause an error where we slightly overestimate the wind force. This error provides an increased margin of safety, so it is a 'good' error.
The dimensions of a 1,000 gallon tank are 16 feel long 41" (3.5') in diameter, and its weight empty is 1,750 lbs. Assuming we need to resist 160 mph wind (category 5 hurricane), we plug the information in the Shed calculator and find that the force to resist is 4,260 lbs vertical and horizontal. See calculator set up below.
Next we need to determine how the tanks can be secured to the anchors. Most tanks come with 4 legs with mounting holes. The Shed calculator assumes that the shed is not all that rigid, and therefore calls for a total of 12 anchors to distribute the forces all around. However, in the case of a rigid steel tank, we can limit the anchoring locations to 4 anchors.
NOTE that using the legs for securing the tank requires that the tank be moved to sit on top of the anchors after the anchors were installed.
The wind can come from either side of the tank, resulting in the full load being applied to only one side of the tank. For this reason, each anchor needs to handle half of the expected lift force, namely 2,130 lbs. Thus the anchor choice is either (4) SP18 anchors or (4) SP58 anchors. Note that the clearance holes in the legs (where the bolts are run through to the anchors) need to be at least 3/ 4" for the Sp18 and 7/ 8" for the SP58. The oversized clearance holes make it easier to align the bolts with the anchors.
The wind can come from either side of the tank, resulting in the full load being applied to only one side of the tank. For this reason, each anchor needs to handle half of the expected lift force, namely 2,130 lbs. Thus the anchor choice is either (4) SP18 anchors or (4) SP58 anchors. Note that the clearance holes in the legs (where the bolts are run through to the anchors) need to be at least 3/ 4" for the Sp18 and 7/ 8" for the SP58. The oversized clearance holes make it easier to align the bolts with the anchors.
Another method of securing the tank to the asphalt is using straps. The advantage of this solution is that the straps can be added after the tank has been in place. When using straps, pay attention to the pre-stress force applied to the anchors by the straps. Ideally the straps should not apply more continuous force than 20% of the pull-rating of the anchors. Allow some leeway for the straps to contract as the temperature drops.