Strips Zones

Strip Zones are intended to provide additional or increased reinforcement in a single direction. An example would be the provision of additional reinforcement to deal with the sagging moments found in column strips in the slab. Strip zones are created by selecting lines which define the position and orientation of the strip zone of reinforcement

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

The left hand pane displays the design calculations. The central pane displays the graphics view of the model. The graphics windows can be controlled by the menus as in Masterframe. The right hand pane contains the controls for adding Strip zone, defining the design parameters for the Peak zones, carrying out the autodesign and displaying a range of results to assist in investigating the design.

Basic Controls - Adding, Copying and Deleting Strip Zones

The basic controls for adding, copying, deleting and selecting strips 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 Strip Zones

A new Strip Zone is added by first clicking on the  icon. This will add a new item to the list of strip zones 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.

With no strip zone defined, the software notes in the output/calculation screen that the strip has not yet been defined.

The properties for a Strip zone design can be set before assigning it to an FE surface or drawn region, or, alternatively, the strip 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 parameters. When a strip zone is added, the graphics window will update to display the position of the strip zone.

Strip zones are not associated with a single FE surface. Therefore, it is possible to create a strip zone which runs across the boundary of the slab. However, care needs to be taken when doing so if slabs have different thicknesses or if there are releases on the interface of the FE surfaces.

When creating a new strip, the first step is to select an FE surface which lies in the same plane as the strip. The FE surface selected only defines the plane of the strip and the strip does not have to lie within this FE surface. The FE surface is selected using the mouse pointer. The FE surface will highlight when the mouse is adjacent the FE surface boundary and is then selected using the left mouse button. When the FE surface is selected, the surface name will appear in the Parent Surface row within the properties panel on the right hand side of the screen.

Strips are created graphically in the graphics window. Strips can be created by either drawing the centreline of the strip and then defining the widths of the strip at the ends, by drawing a rectangle by selecting points on the FE surface by selecting points that represent opposite corners of the strip, or by using a member within the FE surface to define the centreline of the strip - the selected member does not have to be an attached beam so FE Dummy Members can be used for this purpose. The placement method is selected in the Place Current Design Strip Reinforcement area.

Once the required method is selected, the strip is created by clicking on the  icon and then selecting the required points on the FE surface.

A strip can be repositioned (and the selection method changed) by amending the placement mode and then clicking on the  again and recreating the strip. Alternatively, the Edit tools can be used to amend the position and orientation of the current strip.

Once a strip has been positioned on the FE surface(s), it will be shown on in the graphics window and the calculations will update to reflect the design under the current parameters. The properties for a Strip zone design can be set before creating it, or, alternatively, the Strip zone can be created first and the design parameters set afterwards.

Strip Zone Properties

The design parameters of the Strip Zones are set in the design parameters input area. This is the area below the Strip Zone 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 Peak Zones properties area contains input to control how the peak zones are defined, whether the design is to be automatic or manual, definitions for the reinforcement placement relative to the FE surface local axes definitions of the reinforcement in the top and bottom layers and controls for how the design forces are derived. Alternatively, highlight a row within the table and use the up and down cursor arrows to navigate through the list of inputs.

General

The General input allows controls the basic design parameters of a strip zone as well as providing controls over the extend of the strip. The General Region also provides controls over the arrangement of the reinforcement including the position and orientation of the reinforcement within the strip.

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

Add or Replace Basic - defines whether or not the peak zone rebar replaces or is in addition to the basic reinforcement

Parent FE surface at node - sets the FE surface that the strip zone is associated with (for the purpose of defining the plane of the strip)

Auto Design and Bar Arrangement

The Auto Design and Bar Arrangement inputs control whether or not the reinforcement in the strip is designed using the Auto Design, specified by the user (No Auto Design) or uses a mix of user specified reinforcement and auto design. The layout of the area is shown below.

The bar sizes and spacings are defined in the Defaults area. However, by adding bar and spacings dimensions in the Bars Sizes and Bar Spacings row, it is possible to further control the allowed bar arrangement and sizes for use with the auto design. Multiple bar sizes and.or spacings can be input by separating the required dimensions, separated by commas.

The Auto Design options are selected by highlighting the Bar Arrangement row and selecting the required options. These are:

Fixed bars (No auto design) - strip zone reinforcement is specified by the user with no auto design for the reinforcement. No bar size or spacings input appear with this option

Auto design bars (no fixed) - reinforcement design will be done by the software. Reinforcement size and spacings will be based on Defaults setup but can be refined by Bar sizes and Bar Spacings inputs

Fixed + Auto Design additional - for use with the "Replaces basic rebar" option. Fixed bars are specified and if not sufficient the auto design will calculate additional reinforcement required

Unlike the Peak Zones, there is no option to Auto Size the strip. The strip width is controlled by the user either by using the rectangular input option when creating the strip or by using the inputs in the Geometry area to specify the strip width.

Bars

The Bars input area controls the reinforcement positioning and orientation in the currently selected strip zone. Since strip ones only contain reinforcement in either the top or bottom of the slab and either perpendicular or parallel to the strip axis, the inputs have only a single input for the reinforcement bars. The layout of the Bars area is shown below.

Bar orient. to strip - shows the current orientation of the reinforcement in the current strip

Top or Bottom - indicates the position of the bars in the slab

Cover - indicates the current cover. An input of zero uses the default covers set in the Slab Design Basic Data & Defaults area

Bars - indicates the current bar diameter and spacing for the currently selected strip zone

The reinforcement bars can be input or amended by expanding each row in turn. This is done by clicking on the arrow to the left of the required row. The expanded Bars row is shown below.

Lock auto design bars - locks the current auto design bars so that subsequent auto designs will not change the current defined bars

Bar φ - current bar diameter. Selecting the row gives a drop down from which the required bar diameter can be selected

Bar Spacing - displays the currently set bar spacing. Spacing can be amended by selecting the row and using the drop down to select the desired bar spacing

Design Force

The Design Force provides controls to define how the forces in the selected peak region are averaged 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 selection is to average over the full width. The default layout is shown below.

The options available are:

Use max value (no averaging) - uses the maximum force combination in the strip to design the reinforcement

Average - limit width - user input to define the averaging width per zone in metres

Average - limit effective depth multiple - averaging is carried out over a width equal to the specified multiples of the effective depth

Average over full width - averages the forces over the full width of the strip

The aim of the averaging width is to prevent the case of specifying wide zones and so averaging the forces over a large width which may lead to over reduction of the design forces.

Geometry 

The Geometry area provides input to control the width of the strip zone. The layout of the Geometry area is shown below.

Width start side 1 - shows the current width of the strip on side one at the start of the strip

Width end side 1 - shows the current width of the strip on side one at the end of the strip

Width start side 2 - shows the current width of the strip on side one at the start of the strip

Width end side 2 - shows the current width of the strip on side one at the end of the strip

Start x.y (m) - indicates the start position of the strip in the FE surface local coordinates

The shape of the strip zone can be amended by manually inputting a value for the width strip for the 'left' and 'right' sides of the strip at the start and finish of the strip. Alternatively, the strip shape can be modified by using the grips in the graphics display to amend the layout of the strip zone.

The position and extent of the strip can be modified by redrawing, or by using the grips on the boundary and amending the position graphically. However, for small values of change, modifying the start and finish coordinates can allow for a more refined level of control over the positioning of the strip. Each of the Start and Finish input rows can be expanded by clicking on the arrow to the left of the row. The expanded Start x.y (m) row is shown below.

The x and y coordinates can be manually entered to modify the start coordinates. The End x,y(m) inputs are the same format.

Reinforcement Auto Design

If the reinforcement in the peak zones is set to auto design and the parameters have been defined within the Auto Design area, the auto design is then carried out using the options provided within the Auto Design menu area. The layout of this area is shown below.

The Defaults area can be accessed by clicking on the  icon. This will open the Slab Design Basic Data and Defaults menu, which can also be accessed by selecting the  icon. This area allows the default parameters for design to be reviewed or defined.

The Auto Design can be carried out for individual selected Peak Zone. This is done by selecting the required basic region either graphically or from the list of Peak Zones, then selecting the  icon. To carry out an auto design for all Peak Zones, select the  icon. Finally, to carry out the auto-design for all reinforcement zones, select the  icon.

Further control over the areas the auto design is carried out for can be achieved by using the Visible Only check box. The basic functions of the autodesign modes remain the same, but they are limited to only those which are currently visible on in the graphics display. For large models, the auto design can take a significant amount of time to complete and it may be desirable to limit the amount of the model for which the auto design is carried out at any one time by using the Masterframe viewing tools to carry out the auto design for parts of the model.

The Scan for failures option will scan all reinforcement regions and zones and identify those for which the current specified reinforcement is not satisfactory. After a scan for failures is complete. each subsequent press of the Scan icon will jump to the next region or zone for which the design fails.