This is a new feature that has been rolled out to a limited number of customers for testing. Please contact Neara if you are interested in testing this feature.
Note FEA is required to calculate the creep for any strain sections where the Cable Model Type is set to Creep Proportional To Tension. Any static analysis calculations will give the same result for before and after creep.
Conductor Library
These properties are shown in the Conductor Library when the Cable Model Type is set to Creep Proportional To Tension.
Parameter | Description |
Modulus of Elasticity | This is the modulus of elasticity of the conductor which determines how much the conductor will stretch under load. |
Coeff. of Linear Exp. | This is the coefficient of linear expansion which specifies how much the conductor will change length for a change in temperature. The higher this value is the more the conductor will sag when at maximum operating temperature. See article thermal effects for more details. |
Creep Curve Point Temp. | Creep Curve Point Temp. together with Creep Curve Point Tension define a point that along with the origin (0,0) are used to calculate the applicable temperature offset to use to model creep based on the tension in the creep environment. |
Creep Curve Point Tension | See Creep Curve Point Temp. above. |
Theory
Creep Proportional To Tension is a method of modelling creep so that it is a function of tension where a higher tension leads to more creep being applied. This is different to a linear cable model that uses the same creep temperature offset irrespective of the conductor tension.
To illustrate this concept consider the following graph where the Creep Curve Point Temp. is set to 15°C and Creep Curve Point Tension is set to 10kN. A straight line is drawn between the origin and this point as shown below.
For any environments where creep is applied the conductor average axial tension is calculated for the creep environment (with no load factors applied) for each span and then the creep temperature offset is calculated for each span using the below graph. For example if the conductor tension in the creep environment was calculated to be 20kN for a span then a creep temperature offset of 30°C would be applied to that span, and likewise if the tension for another span was 5kN then the creep temperature offset of 7.5°C would be applied to that span.
