Punching Shear

The Punching menu provides tools to carry out punching shear checks at specified locations in the slab and to automatically design any punching shear reinforcement that is required. Punching shear checks are intended for use at the interface of columns and slabs, either where columns are providing support to the slab or in the case of transfer structures where the column is supported by the slab. Punching shear checks can also be applied to the ends of walls.

On first entering the Slab Design Module, the default layout of the Punch area is as shown below.

Basic Controls - Adding, Copying and Deleting Punching Shear Checks

The basic controls for adding, copying, deleting and selecting punching shear checks are the icons in the Basic Reinforcement Sets area. These icons are:

 - Add a new Basic Region

 - Copy a region (automatically adds a new region with the same settings as the copied Basic Rebar)

 - Delete a region

 - Select all regions

 - Invert current selection

 - List visible items only (lists only those basic regions currently displayed in the graphics window

Adding Punching Checks

A new Punching Check is added by first clicking on the  icon. This will add a new item to the list of punchings checks and add the default properties to the property panel. Basic calculation pane will also display the default information. The layout of the screen is shown below.

The properties for a punching shear design can be set before assigning it to an FE surface or drawn region, or, alternatively, the punching zone can be created first and the design parameters set afterwards. Changes in the design output are dynamic so the calculation output will automatically update to reflect any changes made in the design parameters. When a punching zone is added, the graphics window will update to display the position of the punching check and the shear force diagram around the valid portion of the punching perimeter.

By using the  icon, punching checks can be added to specific locations within in the model. By using the

Punching Design Properties

The design parameters of the punching shear checks are defined in the design parameters input area. This is the area below the Punching Check names area. The default layout is shown below.

To navigate through the inputs, hover the mouse over the area and use the mouse wheel to scroll up and down.

The Punching Shear properties area contains inputs to control how the punching shear perimeters are defined, definitions for the shear reinforcement placement and controls for how the design forces are derived.

General

The General input provides inputs to amend the name of the punching shear design check, and also provides controls over the reinforcement grade and the FE surface the punching shear check is associated with in the case that the perimeters cross the boundary between multiple FE surfaces.

Name - Each Peak zone will be named automatically and incrementally numbered. To amend the name, select the row and input the desired naming

Bar Grade - sets the grade of the reinforcement for the punching shear bars for the currently selected punching zone. Set to Default to use the default bar grade.

Parent FE surface at node - sets the surface the peak zone is assigned to for use with peak zones at or adjacent to FE surface boundaries

Shear Bars

The Shear Bars input area provides controls over the auto design for the punching shear reinforcement including inputs to define the minimum bar diameter, the bar angle (for inclined bars) and the layout arrangement of the shear reinforcement where it is required.

The layout of the Shear Bars area is shown below.

Min Bar dia. (mm) - the current minimum bar diameter. The default value can be set in the Defaults area (go to Defaults>Grades and Cover).

Bar Angle (deg) - shows the current bar angle (relative to vertical) in degrees

Shear rebar layout - displays the current set shear reinforcement pattern

There are four available patterns for the shear reinforcement. The patterns are:-

Equally spaced on the perimeter

Radial arrangement

Even grid

Cruciform

Where shear reinforcement is required, the left hand pane graphics will display the shear reinforcement in the selected pattern.

Design Force

The Design Force provides controls to define how the shear forces in the selected punching shear check are derived for the purposes of the reinforcement design. The required option is selected from the Design Force drop down by selecting the row and then using the drop down to select the required option. The default layout is shown below.

The options available are:

Use Code method - the shear force on the punching shear perimeters is derived using the shear and moments based on the calculation methods from the design codes

FE Shear Forces - the shear forces are derived on the perimeters directly from the FE analysis results

When using the FE results, the Design Force area amends to include an input to define the width over which the shear forces are to be averaged. The amend layout is shown below.

The averaging width is specified as a multiple of the slab effective depth. The default value is 2 times the effective depth.

Geometry 

The Geometry area provides inputs to define the column size and to include for an additional drop in the slab to assist with the punching shear capacity. The layout of the Geometry area is shown below.

Column Width (mm) - input the width of the column. An input of zero will use the column width as defined in the model

Column Depth (mm) - input the column depth. An input of zero will use the column depth as defined in the model

Drop projection (mm) - input the projection from the column face of any drop thickening

drop thickness (mm) - input the additional thickness of the slab at the drop position

For models with columns included, the software will use the column dimensions when determining the punching shear perimeters. However, where slabs are modelled without columns, the Geometry input area allows the punching perimeters to be adjust to account for the column dimensions.

In cases where it is not possible to achieve a punching shear design, additional drops can be added to assist with the shear capacity. These drop are intended only for the purposes of shear capacity and do not adjust the slab stiffness and so do not alter the bending moments in the slab.

Auto Design

The design of the punching shear is automatic, with no input options available for the user to define the reinforcement. Therefore, when in the Punching Shear area, the Auto Design options for the punching shear sets as greyed out, with only the ability to design all reinforcement (Peak, Strip and any basic areas set to auto-design) remaining active. Where changes are made in other reinforcement that would affect or amend the punching shear design, the punching shear designs will update automatically.