Shear reinforcement

Principles for the definition of shear reinforcement

In principle, there are two approaches to defining shear reinforcement, one simplified and one detailed. The simplified approach is suitable for a preliminary calculation, for example, and is subject to certain application limits explained in more detail below.

In the simplified approach, only the resulting center line of one or a series of reinforcement stirrups is defined, whereby the number of represented stirrup flanks can be defined in the direction normal to this in the corresponding property set.

In the detailed approach, the stirrups are drawn with their corresponding dimensions (usually as rectangles) at the positions at which they are laid (the number of stirrup flanks is one in this case).

It is possible to use the two approaches in parallel in different areas within a cross-section.

A separate property set must be created for each property set boundary line (center line and rectangle) in any case.

Furthermore, a separate property set must be defined for each shear effective area within a cross-section (e.g. one for a rectangular cross-section and two (one per web) for a single-cell box girder cross-section).

Note: The shear effective areas are determined by the program via the distribution of the unit shear stresses on the cross-section and can also be displayed graphically in the Analysis/Cross-sections menu.

In principle, when defining the shear reinforcement (and using the relevant approach), it should be noted that only those property set lines that project into the area of both the compression and tension chord are taken into account in the calculation (only then is the stirrup considered effective in terms of the truss model). In ALLPLAN Civil, this area of the compression chord is defined from the compressed cross-section edge to the center of compression (Fcd) plus h/10 (where h is the cross-section height in the direction of the resulting acting shear force). Similarly, the area of the tension chord is defined from the drawn cross-section edge to the center of tension (Ftd) plus h/10.

Note: To determine the minimum web width, orthogonal sections are made in the area of the connecting line of the center of compression and tension to the resulting shear force and intersected with the boundary lines of the cross-section.

Necessary steps/inputs for defining shear reinforcement:

1. Creating a property set in the “shear reinforcement” category (for each shear effective area)
2. If necessary, activate/select the property set in the navigation tree (is automatically active immediately after creation) and draw a property set (boundary) line for this shear effective area, layer, which represents the stirrup in detailed or simplified form (rectangle or center line)
3. Definition of the following properties in the properties window of the defined property set:

   Note: It is essential to enter the bar diameter, the number of reinforcement bars, the stirrup offset and the material (as well as the bar size for AASHTO LRFD).

Bar diameter

Bar diameter of the stirrup reinforcement

Bar size [for AASHTO LRFD only]

Selection of bar size according to AASHTO LRFD

Number of reinforcement bars

Number of reinforcement bars in the section through the property set per intersected line (e.g. simplified approach for a stirrup defined as a center line): number = 2, detailed approach for a stirrup defined as a rectangle: number = 1)

Material

Material of the reinforcing bar (selection after definition or import in the Analysis/Material menu)

Stirrup offset

Spacing of the reinforcement stirrups in longitudinal direction