Slab item properties

Tekla Structural Designer
2021
Tekla Structural Designer

Slab item properties

General
Name The automatically generated name for the slab item.
User Name Can be used to override the automatically generated name if required.

Rotation angle

(one-way slabs)

or

X direction

(two way slabs)

This property is used for the following where appropriate:
  • Span direction for 1-way load decomposition
  • To determine the 2D solver element local axes in the solver model
  • Bar direction for Slab on Beam and Flat Slabs.

Different angles can be specified for different panels within the slab.

Note: When SpanDirection is switched on in Scene Content, the rotation angle/X direction is represented by a blue arrow.

See: Rotation angle for slab items and panels and Modify slab/panel span direction

Include in diaphragm If this option is cleared, the slab item does not participate in diaphragm action. All nodes linked to the mat item will be able to displace independently of the diaphragm.
Override slab depth By default all panels in a slab adopt the same depth. Checking this option allows the selected panel to have a different depth and vertical offset.
Vertical offset

Only available when ‘Override slab depth’ is checked.

A positive offset raises the slab panel surface, a negative offset drops it.

Note: Vertical offsets are not structurally significant
Auto-design

For panels in Auto-design mode, As,prov is increased until either a pass is achieved or the limiting reinforcement parameter limits have been exceeded.

For panels not in Autodesign mode, the result will be a pass or fail.

Select bars starting from This option controls the starting point for auto-design procedures.
Plane Indicates the level at which the slab is placed.
Slab general
Name The automatically generated name for the mat item.
User Name Can be used to override the automatically generated name if required.
Slab type
  • Precast
  • Steel deck
  • Timber deck
  • Composite slab
  • Foundation mat
Deck type The deck type depends on the slab type as follows:
  • Precast concrete planks: Precast,
  • Steel plate: Steel deck,
  • Timber: Timber deck,
  • Profiled metal decking: Composite slab,
  • Reinforced concrete: Slab on beams, Flat slab, Foundation mat
  • Post tension: Slab on beams, Flat slab, Foundation mat
Note: Design of post tensioned slabs is beyond scope in the current release.
Decomposition Decomposition choices depend on the slab type as follows:
  • One-way only: Precast, Timber deck, Composite slab
  • One-way or two way: Steel deck, Slab on beams
  • Two-way only: Flat slab, Foundation mat
Slab parameters
Slab properties (general)
Overall depth Specifies the slab thickness.
Diaphragm option
Sets the default diaphragm action for all slab items within the parent slab.
  • Rigid
  • Semi-rigid
  • None
Slab properties (concrete slabs)
Concrete type

• Normal

• Lightweight

Grade/Concrete class Specifies the concrete grade.
Concrete aggregate type Specifies the aggregate type.
Concrete density class For normal weight concrete only, specifies the density class.
Dry density Specifies the dry concrete density
Wet density Specifies the wet concrete density
Long term elastic modulus = Ecm divided by...

composite slab and precast only)

Factor by which the short term elastic modulus is divided to obtain the long term modulus .
Ponding allowance option, Ponding allowance value

(composite slab only)

If required, choose either value or percentage and then specify actual ponding allowance accordingly.
Apply ponding to construction stage

(composite slab only)

  • On = ponding allowance applied at construction stage
Apply ponding to composite stage

(composite slab only)

  • On = ponding allowance applied at composite stage
Decking properties (where applicable)
Country, Manufacturer, Reference, Gauge Defines properties of decking (where applicable).

Reinforcement in slab for crack control or fire requirements

(composite slab, and precast with topping specified only)

Type, Rib type, Mesh type Class, Bar size Defines reinforcement for crack control or fire requirements
Topping details (precast only)
Topping
  • None
  • Non-structural
  • Structural
Depth Depth of topping when topping other than 'None' is selected.
Analysis parameters (two-way slabs)
Orthotropic By default, the slab item is treated as having isotropic material properties. Checking this option allows assigning orthotropic material properties.
Calculate properties

Only available when ‘Orthotropic’ is checked.

Allows setting material properties in two in-plane directions automatically based on the stiffness modification X and Y factors below.

Note: For a detailed explanation of how the parameters are calculated, please refer to Orthotropic slab implementation
X factor and Y factor

Only available when ‘Calculate properties’ is checked.

Applies stiffness modification factors in the local X and Y directions

Note: Applying the same stiffness modification factors in both directions is an alternative way of specifying stiffness adjustments of isotropic slab items.
Ex, Ey, Gxy, Gxz | Gyz, 𝜈x, and 𝜈y

Allows manually setting material properties, such as Young’s moduli, shear moduli, and the Poisson’s ratio.

The fields become editable when ‘Calculate properties’ is unchecked (except 𝜈y, which remains read-only).

Note: No distinction is made between Gxz and Gyz out-of-plane shear moduli.
Apply modification factors

By default, the modification factors are applied. Unchecking this option ignores the modification factors for the slab item.

See: Use of modification factors and Analysis Settings

Design parameters (Head Code Eurocode)

Permanent load ratio

You are required to supply a value for the permanent load ratio parameter. A default of 0.65 has been assumed, but you are advised to consider if this is appropriate and adjust as necessary.

Maximum crack width

• 0.2

• 0.3

• 0.4

Deflection parameters
Restraint constant

(ACI only)

See: Restraint constant (ACI)
Restraint type

(Eurocode only)

See: Restraint type (EC2)
Cement class

(Eurocode only)

See: Concrete Properties (Eurocode)
Material properties
Modulus of elasticity, Poisson's ratio, Shear moduls, Coefficient of thermal expansion Properties specific to timber and steel decks.
Design parameters
Adjustment ratio direction X ,Adjustment ratio direction Y

(slab on beam only)

These factors are applied to the enclosing lengths in X and Y in order to manually adjust the X and Y direction span in the span-effective depth check.

See Slab on beam idealized panels

Enclosing length X, Enclosing length Y

(slab on beam only)

The automatically calculated span length in the X direction, and Y direction.

See Slab on beam idealized panels

Adjusted length X, Adjusted length X

(slab on beam only)

The adjusted span lengths in the X and Y directions.

See Slab on beam idealized panels

Edge category start X, Edge category start Y

(slab on beam only)

The assumed support condition at the start of the span in the X direction, and Y direction.

See Slab on beam idealized panels

Edge category end X, Edge category end Y

(slab on beam only)

The assumed support condition at the end of the span in the X direction, and Y direction.

See Slab on beam idealized panels

Average stiffness ratio

(Slab on beam ACI/AISC only)

In the current release of Tekla Structural Designerr the average stiffness ratio is a user defined value. (Default value = 1.0). The way in which the minimum thickness is calculated directly depends on this value.
Live/Imposed load reduction
Reduce live/imposed loads by

This property is applicable for the design of transfer slabs and mats.

Although the percentage of live load reduction is not determined automatically, this property allows you to specify the percentage manually.

It can be applied to an individual slab item - you don't have to apply a single value throughout a slab or mat (this can be important if you have discrete transfer panels within a large slab area).

• reducible loadcases are reduced

• combinations incorporating reducible loadcases are reduced

• The reduced results are used in slab design.

Note: For mats, the bearing pressures are reduced as well.
Reinforcement

Slabs panels can potentially have 4 layers of background reinforcement, (however any of the layers/directions can be set to “none” if required).

Select/clear Outside layer in X direction as appropriate to indicate if the outside layer is in the X or Y direction. (The outside layer can be set differently for the top and bottom bars if required.)

Utilization ratio
Apply (to autodesign) On
  • When an Autodesign is performed, the design will be incremented to achieve a utilization ratio less than the ratio limit.
Off
  • When an Autodesign is performed, the design will be incremented to achieve a utilization ratio less than 1.0.

See: Apply user defined utilization ratios

Apply (to check) On
  • When a Check is performed, the check will pass provided the utilization ratio is less than the ratio limit.
Off
  • When a Check is performed, the check will pass provided the utilization ratio is less than 1.0.
Ratio limit The utilization ratio against which the autodesign or check is performed (when applied above).
All edges, Edge 1, Edge 2 etc.
Linear Uncheck in order to specify curved edges.
Curvature

Defines the amount of curvature to all edges.

Only displayed when Linear is cleared.

UDA

Name

Finish

Class

Phase

Note

File

A customizable list of the attributes that can be applied to individual members and panels.

See: Create and manage user-defined attributes

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