4.1.1 Options

Options

This section controls the way the design internal forces of result combinations are included in the calculation. This specification also applies when there are several load cases or load combinations to be analyzed in the design case. The Mixed Method is preset: Before the design is carried out, the program finds out if the Enumeration Method or the Envelope Method needs less computing time.

Each load case and load combination selected in window 1.1 General Data is designed individually. A reinforcement envelope is calculated from the results. For result combinations, 16 calculations are performed for the RFEM extreme values of the basic internal forces max/min m_x, max/min n_x, max/min m_y, max/min n_y, max/min m_xy, max/min n_xy, max/min v_x, and max/min v_y.

The enumeration method is precise because every combination is calculated separately and the enveloping reinforcement is determined afterwards. However, it is disadvantageous that the number of the analyzed combinations increases exponentially with the number of load cases as the program proceeds from row to row. If there are 50 selected load combinations, for example, there will also be 50 reinforcement designs. However, the designs cover all possible variants (constellations).

From the load cases, load combinations, and result combinations selected in window 1.1 General Data, the module calculates an internal forces envelope. 16 extreme value variants are analyzed. The difference from the output of extreme values of RFEM result combinations is the following: The add-on module also analyzes extreme value states of the basic stresses that are not only based on the maximum basic internal forces but also on their interaction (for example m_x + m_xy). With this envelope from 16 variants of extreme values, the determination of the reinforcement is started. Hence, 16 calculation runs are carried out to determine the reinforcement. Even if there is a larger number of load cases, load combinations, or result combinations, the computing time is still adequate.

Since an envelope of internal forces is calculated with 16 extreme values, the most unfavorable variants may potentially not be considered, unlike when load cases are computed row by row. Combinations with load cases whose action directions are orthogonal are regarded as critical. In this case, a control calculation according to the enumeration method is recommended.

Before the design is carried out, it is analyzed how many designs with the load cases, load combinations, and result combinations selected in window 1.1 General Data have to be performed per limit state. As mentioned in the Enumeration Method section, each LC or CO is designed separately. For one RC, 16 calculations are required for the extreme value variants of the basic internal forces. If you select one result combination and five load combinations for the design, for example, you get 16 + 5 = 21 calculation runs. As this number is larger than the default of 20 variants of internal forces, the design is carried out with the Envelope Method.

In the input field, you can specify the upper limit of the variants that are designed according to the precise enumeration method.

The Mixed Method is a compromise between precision of results and computation time.

For the design, the module normally uses the RFEM internal forces that are averaged surface by surface: RF-CONCRETE Surfaces transforms the moments and axial forces in the directions of the longitudinal reinforcement and then performs the designs (see chapter 2.5.1).

If the check box in this section is selected, the design is carried out with the internal forces available in the average regions of RFEM.

The average regions are described in chapter 9.7.3 of the RFEM manual.

By means of the averaged results, you can reduce singularities and consider local redistribution effects in the model.

In RFEM, you can model a T-beam by using a surface and an eccentrically connected member of the type rib. The internal forces of the T-beam from surface component and member are determined as rib internal forces by integration of the surface internal forces.

The check box allows you to control whether the surface internal forces assigned to the rib are considered in the surface design. The design with the rib component is preset.