# 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?

2022

Tekla Tedds
Tekla Tedds for Word

2021

Tekla Tedds
Tekla Tedds for Word

2020

Tekla Tedds
Tekla Tedds for Word

2019

Tekla Tedds
Tekla Tedds for Word

2018

Tekla Tedds
Tekla Tedds for Word

2023

Tekla Tedds
Tekla Tedds for Word

2024

Tekla Tedds
Tekla Tedds for Word

Environment

Eurocode

## 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.