Effective Lengths

This mode enables to solve a problem of determining the effective length of members according to the recommendations of Section 6 of SNiP II-23-81* (Section 11 of SP 53-102-2004, Section 10 of SP 16.13330, Section 1.9 of DBN B.2.6-163:2010, Section 13.9 of DBN B.2.6-198:2014), ShNK 2.03.05-13 and EN 1993-1-1. Eurocode 3. This problem is actually a problem of structural mechanics, therefore using the recommendations of Eurocode 3 can not be considered as unacceptable. The result is the value of the effective length factor or the slenderness of the member.

The main window of this mode contains two tabs. The first of them (Structure Type) is used to select a considered structure from the following options:

separate columns or posts;
constant-section frame columns (according to SNiP, SP, DBN and EN 1993-1-1. Eurocode 3);
spatial lattice members made of angles;
stepped columns.

Solutions for truss members defined by Sections 6.1–6.4 of SNiP II-23-81* (Sec. 11.1 of SP 53-102-2004, Sec. 10.1 of SP 16.13330, Sec. 1.9-1.9.4 of DBN B.2.6-163:2010, Sec. 13.1-13.4 of DBN B.2.6-198:2014) are implemented in the Trusses mode.

Once you have selected your structure type, the Structure Properties tab is activated. Its configuration depends on the selected structure type.

If you select the Separate columns and posts structure type, this tab will contain 25 possible conditions of end support.

For the restraint with idealized boundary conditions (the respective button is pressed), the Effective length factor field will display a value that corresponds to the instructions given in design codes. Only the cases when the force is applied to the end are considered.

If the elastic supports with respect to displacements or rotations are selected, you have to specify the numerical data on the stiffness of these supports in the respective text fields. Stiffnesses of elastic linear supports are specified in T/m, and those of elastic rotational supports – in T*m/rad. Once you click the Calculate button, the result calculated by the formulas from the Guide to Design of Steel Structures (to SNiP II-23-81*) will be displayed in the respective field.

In some design models where the restraints are not sufficiently stiff, the column may lose its stability as a rigid body. In such cases the result will be a value of the least critical force causing a deformation of the element.

Once you have selected the Constant-section frame columns type and indicated the frame type (non-constrained/constrained and single-storey/multi-storey), the Effective Length tab will contain the respective design model together with text fields for entering the appropriate initial data. The problem is solved only in the frame plane, and only a stiff connection between girders and columns is considered.

The set of considered problems corresponds to Sec. 6.10* and Table 17, a of SNiP II-23-81* (Sec. 11.3.3 and Table 29 of SP 53-103-2004, Sec.10.3.4 and Table 31 of SP 16.13330, Sec. 1.9.3.4, Table 1.9.8 of DBN B.2.6-163:2010 and Table 13.8 of DBN B.2.6-198:2014). It is assumed that all columns of a frame are of the same stiffness and are loaded by equal longitudinal forces. Therefore Formula (71)* of SNiP II-23-81* (Formula (127) of SP 53-102-2004, Formula (146) of SP 16.13330, Formula (1.9.8) of DBN B.2.6-163:2010, Formula (13.8) of DBN B.2.6-198:2014) is not used. It should be also noted that the concept of a "middle story" must not be used when considering two-storey frames, and in constrained frames the result does not depend on the number of spans. Therefore the respective text field will not be accessible.

Since the effective lengths of the edge and middle columns in multi-span non-constrained frames differ from each other (it is not taken into account directly), we recommend the following procedure: the solution for the middle columns is determined as for a multi-span frame, and that for the edge columns is determined as for a single-span frame. The designations of lengths and stiffnesses on the left from the considered column are used in the single-span frames.

Calculations of the effective lengths for particular segments of stepped columns, out-of-plane columns, and stanchions of flat pillars under conveyor galleries are not performed.

If members of the frame are rolled profiles, their stiffness can be specified by selecting the respective profile from the assortment; to do it, click the button $image\kristall_75.jpg$ . This will open the Select profile dialog box where you can select a desired profile and click the Apply button for stiffness I_y or I_z.

If you have selected Spatial lattice members made of angles as the Structure Type, the Structure Properties tab will contain the designs defined by Sec. 6.5 of SNiP II-23-81* (Sec. 11.2 of SP 53-102-2004, Sec. 10.2 of SP 16.13330, Sec. 1.9.2 of DBN B.2.6-163:2010, Sec. 13.2 of DBN B.2.6-198:2014). The lattice design can be selected by clicking the respective button. Sections for the members are selected from the assortments using the following buttons: Chord, Diagonals, Horizontal. Only equal angles can be used for the chords and horizontals, while the crossing diagonals can be made of unequal angles assuming they are connected to the chord through their narrow legs.

For some configurations, you can select a type of joint at the intersection of the diagonals using the respective group of buttons. At the same time you select the type of forces in the reinforcing member according to Table 14* of SNiP II-23-81* (Table 23 of SP 53-102-2004, Table 25 of SP 16.13330, Table 1.9.2 of DBN B.2.6-163:2010, Table 13.2 of DBN B.2.6-198:2014) (a compressed member, highlighted by a darker color in the respective icon, is under consideration).

You need to choose one of the suggested designs by selecting an appropriate radio button in the Lattice fixation group. It is assumed that this design is applied to both ends of the lattice member. The application does not consider structures where, for example, one end of the member is fixed directly to the chord and the other one is connected by a gusset plate.

When determining the effective lengths and slenderness of space lattice structures from single angles, the program implements various cases of using the stiffness properties of the section (relative to the principal axes of inertia of the section, as well as relative to the structural axes parallel to the legs of the angle) in full accordance with Table 13* of SNiP II-23- 81* (Table 22 of SP 53-102-2004, Table 24 of SP 16.13330, Table 1.9.1 of DBN V.2.6-163:2010, Table 13.1 of DBN V.2.6-198:2014, Table 7 ShNK 2.03.05-13).

Clicking the Calculate button in the Structure Properties tab will display the slenderness values of the compressed chord elements and diagonal elements of space lattice structures, as well as the corresponding effective lengths. Moreover, for the elements of the cross lattice, the program calculates the slenderness and effective lengths both in the plane of the face of the space lattice structure and out of its plane according to Table 19 * of SNiP II-23-81 * (Table 30 of SP 53-102-2004, Table 32 of SP 16.13330, Table 1.9.9 of DBN V.2.6-163:2010, Table 13.9 of DBN V.2.6-198:2014, Table. K.1 Annex K ShNK 2.03.05-13).

If you have selected the According to Eurocode 3 for frames mode, the Effective Lengths tab will contain a model of the considered post with its adjacent girders and columns.

Data on the length of the post, L, and its stiffness, J, are specified in the respective text fields. If the post has a rolled section, its stiffness can be entered automatically after selecting the section from the assortment (using the button $image\kristall_75.jpg$ ).

The table of properties of the surrounding members is used to enter the data on the length of the members, conditions of their abutment (rotation) on the end opposite to the post, stiffness and the compressive force value. If any of the members is absent (is not checked in the first column of the table), the respective text fields will be inaccessible.

All the calculations comply with the recommendations from Annex E of EN 1993-1-1.

Selecting the Stepped columns structure type invokes the Structure Properties tab containing 4 possible conditions of end support:

1) clamped at the bottom and free at the top;

2) clamped at the bottom and fixed against rotation at the top;

3) clamped at the bottom and hinged at the top;

4) clamped at both ends.

This tab also contains the Loads and Segment Properties tables, where you can specify properties of segments of a stepped column (cross-sectional moments of inertia and lengths) and the values of concentrated forces applied at the top of segments of the stepped column.

Clicking the Calculate button will display values of the effective length factors of segments of stepped columns determined in accordance with the selected design codes.