Why are the results of members and set of members different in design?

Answer

This is because the effective lengths or buckling lengths of members and sets of members differ. While the effective length is used for the stability analysis for members, RFEM takes the length of the summarized members for the set of members.

Example

The frame shown in Figure 01 consists of a horizontal beam that is divided into four equally long members. In addition, a set of members is created for the four members. The stability analysis is performed according to the equivalent member method for both cases.

For the design of members, the program calculates with a length of 1.00 m in each case. In contrast, the set of members has a length of 4.00 m (see Figure 02). This difference in length naturally affects the stability design, which means that the capacities are also different (see Figure 03).

In addition, it is not recommended to calculate all members and sets of members in a single design case because this leads to falsified results.

Keywords

Member Set of members Difference Member Set of members Calculation Stability

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