Axial Force and Effective Tension |
 
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Axial Force and Effective Tension |
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The relationship between axial force and effective tension is expressed as follows:
(1)
where:
•
is effective tension
•
is axial force
•
is internal pressure
•
is the corresponding internal area
•
is external pressure
•
is the corresponding external area
In Flexcom, the axial force in an element is a solution variable, and the effective tension Te is calculated from N using the above relationship. Note that 
is calculated from the buoyancy diameter Db you specified as part of the Geometric Properties definition.
In some analyses the choice of Db for input to Flexcom means that the axial force calculated by the program is not a true reflection of the force in the actual wall structure. Obviously, the choice of buoyancy diameter will be governed by the need to ensure that effective tensions in the model are everywhere correct.
If you define an effective external diameter Do to be used in Stress Computations, and if this value is not equal to the buoyancy diameter Db you specified as part of the geometric properties definition, then Flexcom recalculates the axial force in the section on the basis of the effective diameter Do. Specifically, the axial force is calculated using:
(2)
where 
, 
and 
are as previously, but 
is now calculated from the effective external diameter using:
Note that this recalculation of axial force takes place automatically whenever you specify a Do that is not equal to Db. Note also that if you request a plot of axial stress, this will naturally be computed using the recalculated axial force.
•*GEOMETRIC SETS ($MODEL) is used to assign geometric properties to element sets, including buoyancy diameter Db
•*PROPERTIES ($MODEL) and *PROPERTIES ($DATABASE POSTPROCESSING) are both used to assign effective structural properties to element sets for use in calculating stresses, including external diameter Do.
