We have just released a new version of ITSdesign that has a Jack Rafter System. This allows you to use a single center column on tanks as large as 90' to 100' diameter. With this system half of the rafters go from the center column to the shell. In between each of these Thru Rafters is a Girder that is made from a small channel and is located at approximately the mid point of the Thru Rafter. From the center of the Girder to the shell is placed a Jack Rafter. Thru Rafters get to be quite heavy but the Jack Rafters are relatively small. It does increase the load on the center column and on the soil below the column. However, the cost savings can be significant as you do not need intermediate columns. It also reduces the diameter of the cap plate on the center column considerable. The erection cost for this type of system is less than for one with intermediate columns.
If you haven't downloaded a free trial copy of ITSdesign, do so today and give this new system a try. Just go to www.innnovativetanksolution.com and click on the ITSdesign download button. Follow the instructions for installing the trial program.