I would like to report a possible error in RF-CONCRETE Columns in RFEM 5 when designing a slender reinforced concrete column according to ACI 318-19.
I prepared a simple verification model based on the example presented in the Dlubal Knowledge Base article:
Stability of Reinforced Concrete Structures: RFEM vs ETABS” – KB 002069
The model parameters are:
- rectangular RC column: 1000 × 1000 mm
- column length: 8.50 m
- concrete: f'c = 40 MPa
- reinforcement: approximately 1%
- axial force: Pu = 10,000 kN
- bending moment: Mz = 3,000 kNm
- nonsway column
- effective length factor in the governing direction: kz = 2.0
- effective length: kz·L = 17.0 m
- βdns = 0
- Cm,z = 1.0
RF-CONCRETE Columns correctly recognizes the column as slender in the z-direction:
λz = 58.89 > λlim,z = 22.0
and calculates:
Pc,z = 46,197.1 kN
However, the program then gives:
δz = 1.0000
and therefore:
Mc,z = 3,000 kNm
i.e. no moment magnification is applied.
Additional inconsistency in the detailed output
There is also a second inconsistency in the detailed calculation output.
For the governing z-direction, RF-CONCRETE reports:
M_(2,z)=3,000 kNm
M_(2,min,z)=452.4 kNm
so clearly:
M_(2,z)>M_(2,min,z)
However, in the detailed output RF-CONCRETE first states:
“Was the minimum moment applied in this direction? – Yes”
while a few lines later it asks:
“Is the design moment M_(2,z)smaller than the minimum required moment according to 6.6.4.5.4?”
and answers:
“No”.
These two statements appear contradictory.
Since:
3000 kNm>452.4kNm
the minimum moment should not govern the design in this direction.
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