Punching Shear

The punching shear design checks are intended to carry out the required punching shear design checks at support points or points of localised high loads, such as over the head of columns or support points, at the ends of shear walls, or under transfer columns. The punching shear design is based on the concrete slabs effective depth and the defined reinforcement applicable to each punching shear check applied to the slab. The punching shear check involves a check on the perimeter of the column and then check on subsequent punching shear perimeters. The design shear force can be derived from the Code methods or directly from the FE analysis results. The punching shear check allows the user to define both the arrangement of shear reinforcement using a drop down of pre-set arrangements and to also indicate a shear bar reinforcement angle should if inclined reinforcement is to be used. The punching shear check provides inputs to define the column cross section (which defines the punching perimeter) for cases where a nodal support is used rather than modelling the column. Finally, the punching shear check provides inputs that allow the user to specify a drop in a slab to provide enhanced punching shear resistance.

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Contour Unity Ratios Only Consider Basic / Peak / Strip Values, and do not include any additional shear reinforcement, therefore specifying additional punching and linear shear reinforcement does not affect the unity ratio contours in the output.

As such, these plots should be interpreted as warnings rather than final design checks.

Punching Shear Settings

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

- allows multiple regions be be selected graphically using the mouse to select the locations 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

icon, it is possible to select multiple points, either by clicking each point in turn, or by holding down the left mouse button and windowing a region of the model.

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.

Drawing Options

The Drawing options area provides options to show a graphical summary of the design results. The summary results can be displayed for reinforcement areas provided, design utilization or unity ratios and design forces from the FE analysis. The graphical results can be shown for a specific design zone, for all the design zones of a specific type, or for all design zones.

The basic options for results display are the same for each of the Basic Rebar, Peak, Strip and Punching zones. When in the Peak, Strip or Punching shear menus, the Drawing Options will include options to control the section diagrams for these reinforcement zones while the strip zones also includes an option to display local FE surface nodal coordinates to assist with defining the start and end coordinates.

The layout of the area when in the Basic Rebar menu option is shown below.

The drawing options are:

Rebar areas - shows the current reinforcement areas
Unity - displays the current design utilization or unity ratio
Force/Capacity - displays the FE analysis results

Each drawing option is selected using the radio buttons. For each option, the output to show is then selected from the drop down selection.

For each output option, the results can be displayed for the following options:

Selected - displays the results for the currently selected rebar zone
All sets - displays the results for all sets in the current selected Rebar Type e.g. in the basic rebar this option will display all basic rebar zones
All - displays for all rebar zones currently created in the model regardless of zone or type.

In both the Peak and Strip reinforcement areas, display options are available to control the section diagrams associated with these rebar zones. The layout of the Drawing Option are when these options are displayed is shown below.

The scale of the section diagram is adjusting using the drop down menu. The section diagrams are turned on/off using the Draw checkbox. Checking the Values checkbox will include results values in the section diagrams.

Slab Image – Shear Unity Ratio Contour Plot

MasterSeries provides graphical contour plots to help users quickly identify areas of an FE slab that may require more detailed shear assessment. In particular, the Shear Unity Ratio Contour highlights regions where the basic unreinforced shear capacity of the slab is exceeded, acting as an initial screening tool.

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The shear unity ratios shown in these contours take into account the effects of basic, peak, and strip reinforcement definitions, but excluding any applied punching or linear shear reinforcement within defined software zones. As such, these plots should be interpreted as warnings rather than final design checks.

Specifically:

Punching shear reinforcement is not included within the punching shear perimeter (typically at u₁ or 2d), and support face enhancement effects are also excluded.
Linear beam shear reinforcement is not considered. For transfer slabs, the contour is therefore often governed by the basic linear shear capacity, which is intentionally more onerous and conservative than the punching shear assessment close to the column.

The Shear Unity Ratio Contour outputs are intended to flag potentially critical regions and prompt the engineer to carry out the appropriate detailed punching or linear shear checks, rather than being used directly for design acceptance.

Rebar Areas

The Rebar Areas display uses colour coding to indicate the reinforcement in directions 1 or 2 for the top or bottom reinforcement. A typical layout of results is shown below.

Unity

The design unity values displays the ratio of the design forces to the design capacity for the selected results. This graphical output options are:

None - no results are displayed

Mr Unity Hog xx - shows the maximum unity ratio for the hogging moments in the xx direction
Mr Unity Hog yy - shows the maximum unity ratio for the hogging moments in the yy direction
Mr Unity Hog max - shows the maximum unity ratio for the hogging moments in the either the x- or y-directions
Mr Unity Sag xx - shows the maximum unity ratio for the sagging moments in the xx direction
Mr Unity Sag yy - shows the maximum unity ratio for the sagging moments in the yy direction
Mr Unity Sag max - shows the maximum unity ratio for the sagging moments in the either the x- or y-directions

If modification are made to the design, the graphics can be updated using the icon. Peak values can be indicated in the graphical window by check the Draw Values checkbox.

A typical screen layout with the Mt Unity Hog max results displayed is shown below.

Force/Capacity

The Force/Capacity display options allows a number of the FE analysis results to be viewed while in the slab design module. The available results are:

Mx Top (Wood Armer)
My Top (Wood Armer)
Mx Bot (Wood Armer)
My Bot (Wood Armer)
As req Top xx
As req Top yy
As req Bot xx
As req Bot yy
As prov Top xx
As prov Top yy
As prov Bot xx
As prov Bot yy
Mr Hog xx
Mr Hog yy
Mr Sag xx
Mr Sag yy

If modification are made to the design, the graphics can be updated using the icon. Peak values can be indicated in the graphical window by check the Draw Values checkbox.