Helical strakes can be added in MECASTACK.  Go to the “Design” “Damping” menu, and then there is a helical strake option.  The button at the right “Damping Device Menu” lets you enter the parameters.   Although MECASTACK does let you simulate helical strakes, their use still requires some engineering judgment.  The software will consider the additional along wind loads, by considering the higher shape factor that is entered on this "Damping Device Menu" (Default Cf = 1.4).  as far as Vortex Shedding is concerned, the software assumes that you know what you are doing by adding the  helical strakes, the software can not determine how well they will work at addressing vortex shedding.  This is completely a judgment by the user, because there are no equations or methods to predict how effective they will be in suppressing vibration.  There are specific instances where you CAN NOT use helical strakes, such as when you have closely spaced stacks (or other tall structures).  Each code varies in the limit, but generally this is considered unacceptable when the center to center spacing is 10 to 15 diameters or less.  In these instances, a damper or another solution is required.   


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