Control method (Concrete Column)

Last modified by Fredrik Lagerström on 2021/05/27 15:43

Slender bending capacity

The checking is performed according to EN 1992-1-1 5.8. A separate calculation in each principal direction is made as a first step and if a moment is defined in at least one direction a possible biaxial check is also made according to EN 1992-1-1 5.8.9. The program is adding the defined moment to the moment from initial bow imperfection and if the column is defined as slender also calculates a 2nd order moment depending on the user´s choice either according the stiffness method EN 1992-1-1 5.8.7 or the curvature method EN 1992-1-1 5.8.8. Finally the total moment is compared to the moment with regard to unintentional load eccentricity according to EN 1992-1-1 6.1 (4). If no 2nd order effects should be calculated e.g. in order to consider EN 1992-1-1 5.8.2 (6) or the criteria in EN 1992-1-1 the column should be defined as short as then no 2nd order moment will be added. Finally the ultimate bending capacity with regard to the defined reinforcement is calculated and the utilization is presented in each direction.

Method based on nominal stiffness

See Method based on nominal stiffness (Design)

Method based on nominal curvature

See Method based on nominal curvature (Design)

Ultimate moment capacity


Moment capacity in ultimate limit state is most easily calculated with a fixed neutral axis inclination, e.g. parallel to either y or z-axis. As non-linear material and cracking are assumed iteration is required to establish equilibrium together with external normal force and at the same time calculate current moment capacity. Start the calculation by setting maximum allowed strain in extreme concrete fiber (εcmax) and extreme reinforcement bar (εsmax) and calculate force resultants in compression zone and tension zone in order to determine if compression or tension is decisive. Iteration continues with adjustment of neutral axis position to get maximum utilization of decisive materials at established equilibrium conditions.

Moment capacity may also be calculated in an optional direction, either as a fixed neutral axis inclination (other than y or z-axis) or as a fixed moment vector inclination. In the latter case an iteration is generally demanded to establish the neutral axis direction that corresponds to the given moment vector inclination.

Capacity with regard to biaxial bending

See Capacity with regard to biaxial bending (Design).

Combined stress capacity

Maximum compression capacity without and with regard to the current moment is calculated. The area containing reinforcement is reduced from the concrete area in the calculation.

Slender compression capacity

When the stiffness method is used the compression capacity is calculated as the buckling load according to EN 1992-1-1 (5.17). The stiffness EI is calculated as the nominal stiffness according to EN 1992-1-1 (5.21) or the design axial resistance of the section NRd = Ac fcd + As fyd whichever is lesser.

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