Working with Slab Strips

Working with Slab Strips

Slab Strip Properties

 
Slab Strip

The "Slab Strip Properties" will be loaded when the "Slab Strip" option in the "Modelling" ribbon is selected.

The "Slab Strip Properties" has two tabs only.

After arranging the fields for the slab strip form, a new strip will be inserted by dragging two points in the drawing area.

The following fields exist in this form:

Strip Label

The label that will identify the strip can be entered in this field. This field is limited to 3 characters.
Slab strip labels are composed of a positive integer (1 to 999) preceded by the character "x" or "y". The strips along a direction closer to the horizontal must be labelled using "x" followed by the strip number and the strips along the other direction must be labelled using "y" followed by the strip number. The strip numbers need not be successive.

For example, the 3rd strip along horizontal direction will be labelled as "X3" and the 2nd strip along vertical direction will be labelled as "Y2".

A text control spin button exists to the right of the label field to facilitate the creation of successive label text.

Steel Layer

If the strip is set to be  “Manual Strip”, or “FE Strip” with one of the “ Span Band Strip ”,  “ Support Strip ” or “ Fixed Band Strip ” type in the “FE” tab, then define the " St. Layer " number (as " " or " 2  "). Effective depth of the slab will be set based on the layer number entered in this field as follows:
  1. For the 1st layer steel:
    Cover to Bar Center = Concrete Cover + (Bar Size Along Strip / 2)
  2. For the 2nd layer steel:
    Cover to Bar Center = Concrete Cover + (Bar Size Along Strip / 2) + (Bar Size Along the Other Direction)

In slab systems with beams, steel layers will automatically be set using the plan dimensions of the slabs that the strip intersects. According to this, the steel bars that are located along the short span of the slab will have the layer number “” whereas the bars in the other direction are located in Steel Layer “”.

Finite Element Strip

If you are inserting a Finite Element Strip (i.e. the moments will be collected from the finite element analysis results), then check the " Finite Element Strip " option in the Slab Strip Form and select the Strip Type from the " FE  ".

 “Finite Element Analysis of the slab must have been performed in order to continue with the reinforcement calculations. Type of the Finite Element Strip must be consistent with the slab system. 
Type of the Finite Element Strip must be consistent with the slab system.
For example, if you are working with a slab system with beams, the Finite Element Strip type must be “Span Strip”.
Similarly, if the system you are working on is a flat plate, then differing with the location, “Span Band Strip”, “Support Strip” or “Fixed Band Strip” must be selected.
In the case of a Waffle Slab or a Ribbed Slab, “FE Rib Strip” must be used.

Manual Strip

If you are defining a strip to insert steel bars manually, you can check the Manual Strip option.
The Manual Slab Strip dialog will be displayed if this option is checked. You can fill the data fields located in this dialog to display the steel bars associated with this strip.

Slab Strip End Conditions

End conditions at the start and end of the slab strip can be set using the option buttons near the "At Start" and "At End" labels. The axis label will mark the start and an arrow will mark the end of the axis in the plan window.
Available Slab Strip End Conditions are:

   

Prior to inserting the strip, choose:

  1. Cantilever option at start or at end if there is a balcony slab at the respective end of the strip,
  2. Bob option at start or at end if the strip is terminated by a supporting beam (or a support band beam). The top steel bars will be bent at the outer edge of the support beam when this end-condition is used.
  3. Slab option at start or at end if there is another slab at the respective end of the strip. When this option is checked, a new field will appear below the option buttons as b-Slab (At Start) or b-Slab (At End). Enter the dimension of the adjacent slab along the strip in the related field.

An easy way of determining this dimension is clicking to this input field with the mouse and then selecting the slab (by clicking to the label in the plan window). Then the width along the strip will appear.

The top steel bars are extended further into the adjacent slab by the anchorage length set by the user.

After all the slab strips are defined, Slab and Ribbed Slab analysis and design reports can be prepared using the menu options in the "Slab Table" and "Ribbed Slab Table" forms respectively.

Integral Strip

If you are using a "Fixed Band Finite Element Strip", you can check the Integral Strip option if you want to calculated the design moments using integral approach rather than calculating the maximum moments within the strip range.

Number of Longitudinal and Horizontal Axis Point Count

You can set the number of sampling points to be used in the Finite Element Strips along (longitudinal) and perpendicular (transverse) strip directions.

Usage of Slab Strips

Slab Strips are used for creating a means for the analysis, design and curtailment of slabs. Slabs along the strip are determined and their analysis is performed along the strip if the moment coefficients method is selected. Similarly, a continuous beam analysis is performed along the strips if ribbed slabs are encountered.
If the method of analysis is selected to be finite elements, then the design results along the strips are collected from the analysis results based on the type of slab strip set by the user.

The Usage of Slab Strips:

  1. Analysis and Design of Slabs: Slabs and Ribbed Slabs that are found along the strips are analysed and designed. If the strip is a Finite Element Strip, then the analysis results are collected from the finite element model results otherwise, the analysis of the slabs along the strip is carried out using the moment coefficient method.
  2. Insertion of the Reinforcement Bars: Steel bars calculated during the analysis of the slabs are inserted along the strip based on the Strip Type parameter.
  3. Analysis and Design of Ribbed Slabs: A continuous beam model is created along the strip for the analysis and design of ribs.

Steel Bars are calculated only along the direction of the slab strips. For that reason, strips must be defined along both directions for two-way slabs. More than one strip may need to be defined along one direction for L-shape slabs to take into account different spans.

Similarly, more than one strip may need to be defined along slabs with different adjacent slabs along an edge. In such cases, in order to make a correct quantity extraction, slab span lines may need to be manually modified.

Slab Strip Types

Each Slab strip drawn would be automatically considered as a strip for the Moment Coefficient Method, unless the "Finite Element Strip" box is checked. These strips must pass through the slabs supported by beams and walls.
As an alternative to the Moment Coefficient Method, "Finite Element Analysis" can be used.
To define a slab strip for the "Finite Element Analysis", the "Finite Element Strip" box must be checked. 

 Span Strip
 
Span Band Strip
 
Support Strip
 
Fixed Band Strip
 
FE Rib Strip

The "Strip Type Options Buttons" will be loaded within the Slab Strip Properties form when the "Slab Strip" option in the "Member" pulldown (or toolbar) is selected.

Several different slabs strips can be defined based on the usage and position of the strip. When preparing to define a finite element strip, prior to defining the points to insert the slab strip, the "Strip Type" must be set by pressing one of the strip type buttons. If you change the strip type for the slab, press theUpdate button to update.


For a detailed explanation of the usage of slab strips, you can refer to Slab Analysis and Design Overview.
For more detailed explanation of each different type of Finite Element FE Strip, please refer to  Finite Element FE Strip .
When using Analytical Strip and FE strip - (Span Strip), avoid drawing at region where you have multiple slabs inserted between the slab supports (beam/wall).
The slab strips will always design only for the first slab.

Defining a New Slab Strip

Before inserting a Slab Strip:
  1. Beams and columns along the strip must be defined,
  2. Slabs or ribbed slabs along the strip must be inserted.

To define a new Slab Strip:

  1. Press the Slab Strip button located in the "Modelling" ribbon.
  2. "Properties can be accessed by pressing the Slab Strip button.
  3. Set the label of the slab strip to be defined. When automatic labelling is on, the strip labels will be assigned incrementally when a new strip is defined.
    Slab strip labels are formed by a positive integer (1 to 999) preceded by the character " " or " ". The strips along a direction closer to horizontal must be labelled using " " followed by the strip number and the strips along the other direction must be labelled using " " followed by the strip number. The strip numbers need not be successive.
  4. If you are inserting a Finite Element Strip, then select the "Finite Element Strip " option in the Slab Strip Type.
  5. Find the insertion points of the slab strip in the drawing area to insert a new element. You have to drag points to insert the member. If moment coefficients are used, then the analysis of the strip will be performed immediately and the selected reinforcement will be inserted.
  6. While for the Finite Element Strip, please run the FE floor analysis and include the FE Floor analysis result in Strip Results. (as shown in the figure below)


    The insertion points must be selected so that they will pass completely through all the slabs that will be covered by the strip.

Editing an Existing Slab Strip

When a beam or slab along the strip is modified, the strips along these members must be edited. In order to edit an existing strip:
  1. Select the existing slab strip.
  2. Right-click and select Properties. (Propertiescan be accessed alternatively by pressing the “Slab Strip” button).
  3. Modify the fields such as "Label" or end conditions in the "Slab Strip Properties"  form.
  4. Press the "Update" button in the form.

You can repeat this process to as many members as you wish. Only one member at a time can be edited by using this method.

Slab Strip Shortcut Menu

You can access the most often used command options for the Slab Strips in the shortcut menu (displayed by right-clicking the mouse) after selecting a Slab Strip.
A shortcut menu for a single Slab Strip selection includes Slab Strip Check Design and Delete Steel Barsoptions specific to a Slab Strip member. These option will be omitted from the shortcut menu when multiple Slab Strips are selected.

Slab Strip Check Design

Adequacy of steel bars placed in the slabs can be controlled by selecting this option. Calculations will be repeated for that particular slab strip. Slab Analysis and Design Report will be displayed after this operation.
 To perform analysis and design of all slabs and ribbed slabs in the system or in the current storey that are crossed by a slab strip, select Slab Analysis and Design and/or Ribbed Slab Analysis in the Design ribbon.

Delete Steel Bars

If there exists steel bars assigned to a particular Slab Strip, those will be deleted by using this option. 


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