Why is a reduction factor (RF) applied to all columns in Tekla Structural Designer and not the Tekla Tedds "RC column design to EC1992" calculation?
Not version-specific
Tekla Structural Designer
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Question
Why is a reduction factor (RF) applied to all columns in Tekla Structural Designer and not the Tekla Tedds "RC column design to EC1992" calculation?Image
Answer
Tekla Tedds uses a different and more approximate biaxial bending check method to that of Tekla Structural Designer, meaning that a 10% reduction of the concrete strength is not applied in the Tedds software for rectangular sections.Note that the 10% reduction (displayed in Tekla Structural Designer results as a reduction factor RF = 0.9, see screenshot above) comes from the following Clause and rationale:
EC2 section 3.1.7(3):
“Note: If the width of the compression zone decreases in the direction of the extreme compression fibre, the value ηfcd should be reduced by 10%”
This is always applied, the rationale being as follows:
It was decided to always use this reduction for rectangular sections; the general case is biaxial bending and so the axial-moment interaction check is most commonly carried out at some non-zero resultant. Hence, this is conservative only in situations where the concrete area doesn’t reduce – which should generally be rare. Therefore, the reduction should also be applied in the ultimate axial resistance check – which means that the ultimate axial resistance matches the peak position of the interaction diagram.