RF-CONCRETE Members Version 5

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RF-CONCRETE Members Version 5

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3.5 Supports

In this module window, you can define the support conditions for the members. The support nodes of horizontal members taken from RFEM are preset. The program recognizes whether the support is located at the end of a member or between two members (continuous beam).

Support widths greater than zero affect the design (redistribution of moments, moment reduction, reduction of shear force) and the reinforcement proposal (length of anchorage). However, this only applies to members in horizontal or slightly inclined position, not to columns!

Figure 3.25 Window 1.5 Supports
Node No.

This column lists the supported nodes of all members in a horizontal position or a position that is inclined up to 15°. Use the button in this column to select additional nodes graphically in the RFEM work window.

Support Width b

In this column, the widths of the supports must be defined. This way, you can determine, for example, a wall's wide bearing area that is represented as singular support in the RFEM model.

Direct Support

This column controls the support type of the beam. If there is an adjoining beam introducing its load to another beam, the support is an indirect support. In this case, you have to clear the check box.

The specifications affect the lengths of anchorage and the shear force design.

Monolithic Connection

In column D, you can specify whether there is a flexurally rigid connection with the support, or a rotary support allowing for a reduction of the supporting moment.

End Support

The geometrical conditions for end supports are different than the ones for intermediate supports, in order to determine the design moments and anchorage lengths (see graphic on the right in module window).

M Ratio δ

For continuous structural components, you can define the ratio δ of redistributed moment and elastically determined initial moment in column F. You can access the column as soon as the option Consideration of limited moment redistribution below the graphic is selected.

The δ-values can be determined according to a standard, for example EN 1992-1-1, 5.5 (4).

Comment

Here, you can enter a text describing the selected support conditions.

Moment redistribution / Shear force design

Below the graphic, you can find four check boxes whose settings affect the required reinforcement. These settings are generally effective for the current design case (see chapter 8.1).

Consideration of limited moment redistribution of the supporting moments

For continuous beams, it is possible to apply the linear-elastic methods with limited redistribution of the supporting moments. The resulting distribution of internal forces must be at equilibrium with the acting loads. In standards such as EN 1992-1-1, 5.5 (4), the moment ratios δ that must be observed in order to ensure the ability for rotation in critical areas without special designs are described.

RF-CONCRETE Members determines the limit value and compares it with the value specified in column F. Then, the higher value is used for the redistribution.

Reduction of the moments or dimensioning for the moments at the face of a monolithic support

Optionally, RF-CONCRETE Members performs a moment reduction according to, for example, EN 1992-1-1, 5.3.2.2, if all of the following requirements are met:

  • No end support
  • Support width > 0
  • Support is restrained in Z-direction
  • Support force acts positive in Z
  • Member in horizontal position or with max. inclination of 15°
  • Negative moment distribution in entire support zone

The decision whether to reduce the moment or to apply the moment at the face of the support depends on the support's definition in column D: The moment at the face of the support is used for a monolithic connection; the supporting moment is reduced for a support with no rotational restraint.

Shear force design at the support face

A shear force design is possible for the moment at the face of the support. In case of a direct support, it is possible to reduce the design value of shear force according to EN 1992-1-1, 6.2.1 (8).

For result combinations, the shear force design is always carried out on the support's edge because a "uniformly distributed load" cannot be presumed for an envelope.

Reduction of shear forces with concentrated loads near support

Use this check box to control whether the shear force component of concentrated loads close to the support is considered according to EN 1992-1-1, 6.2.2 (6) or 6.2.3 (8). A reduction is only carried out for load cases and load combinations, not for result combinations.