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# 9.3.1 Model in RFEM

### Model in RFEM

By describing the stability analysis of a slender, restrained column, we look at the differences of both approaches regarding the nonlinear calculation according to EN 1992-1-1, 5.7 and 5.8.6.

This model is presented as example 1 in [14].

System and loading

The loading corresponds to the specifications from [14]. In load case 1, the design value NEd = 1059.5 kN is taken into account.

As shown in the figure above, the loading is entered eccentrically. The eccentricity can be determined geometrically or with an additional moment MSd = 1059.5 ⋅ 0.05 = 52.98 kNm. In our example, the load is introduced eccentrically through a short member.

The inclination of the column is considered as an imperfection in load case 2. The value of the inclination is calculated as 1/φ = 1/0.003536 = 282.81.

The concrete's modulus of elasticity is defined with 26230 N/mm2 according to the specification in [14].

Load combinations

For analyzing the load-deformation behavior, we define the following load combinations:

• Design-relevant combination:
 CO 1 LC1 + LC2
• Alternatives:
 CO 2 0.20 ∙ LC1 + LC2 CO 3 0.50 ∙ LC1 + LC2 CO 4 0.70 ∙ LC1 + LC2 CO 5 0.80 ∙ LC1 + LC2 CO 6 0.90 ∙ LC1 + LC2 CO 7 0.92 ∙ LC1 + LC2 CO 8 0.94 ∙ LC1 + LC2 CO 9 0.96 ∙ LC1 + LC2 CO 10 0.97 ∙ LC1 + LC2 CO 11 0.98 ∙ LC1 + LC2 CO 12 0.99 ∙ LC1 + LC2 CO 13 1.05 ∙ LC1 + LC2 CO 14 1.10 ∙ LC1 + LC2

No stiffness reduction by the partial safety factor γM is carried out for the calculation (RFEM default setting).

Results

The calculation with RFEM provides the following internal forces and deformations:

 Load combination Axial force N [kNm] Moment I. Order Theory MI [kNm] Moment II. Order Theory MII [kNm] Column head displacement u [mm] CO 1 −1059.50 82.59 170.58 82.71 CO 2 −211.90 18.55 9.27 CO 3 −529.75 56.18 27.77 CO 4 −741.65 91.27 44.77 CO 5 −847.60 113.28 55.36 CO 6 −953.55 139.33 67.83 CO 7 −974.74 145.12 70.59 CO 8 −995.93 151.12 73.45 CO 9 −1017.12 157.36 76.42 CO 10 −1027.71 160.57 77.95 CO 11 −1038.31 163.84 79.51 CO 12 −1048.91 167.18 81.09 CO 13 −1112.47 186.66 91.29 CO 14 −1165.45 208.71 100.80
Literatur
 [14] Kleinschmitt, Jörrit. Die Berechnung von Stahlbetonstützen nach DIN 1045-1 mit nichtlinearen Verfahren. Beton- und Stahlbetonbau 100 (02/2005)