Precast beam design

Added September 16, 2020 by Tekla User Assistance tekla.documentation@trimble.com

Software version: 
Tekla Structural Designer 2020

Precast beam design

Precast beam design

Specific aspects of the precast beam design workflow in Tekla Structural Designer are described below:

Section shapes

The following section shapes can be used within the Tekla Structural Designer - Tekla Tedds workflow.
  • Rectangular
  • L-Section
  • Inverted L-Section
  • T-Section
  • Inverted T-Section

Beam arrangement

The Tekla Tedds calculations have no concept of the model geometry within Tekla Structural Designer and so there are no limitations on the design of curved beams in both major and minor axes. Continuous beams, cantilevered beams etc. are similarly supported by the workflow.

Concrete type

While you can apply both normal and lightweight concrete in the beam properties, precast beam design using lightweight concrete is currently beyond scope.

Nominal cover

The default nominal top, bottom and side cover values set in Design Settings> Precast> Beam> Reinforcement Settings are automatically passed through to the Tekla Tedds calculation. The nominal concrete cover is the distance between the surface of the reinforcement closest to the concrete surface (including links and surface reinforcement where relevant) and the nearest concrete surface.

Reinforcement - longitudinal bar patterns

Note: The reinforcement regions are considered to be the extent of the effective reinforcement. Anchorage and anchorage lengths are not considered in precast beam design within Tekla Tedds.

In Design Settings> Precast> Beam there is a one Standard Pattern available for top longitudunal reinforcement, Precast Top 1, and one Standard Pattern available for bottom longitudunal reinforcement, Precast Bottom 1 as illustrated in the figures below.

Standard Pattern of Top Reinforcement - Precast Top 1

Pinned span settings are applied to all spans with Fixity end 1 and 2 set to Pin.


Note: As shown above, the concept of continuity bars in pinned spans can be catered for by enabling Bar (12). When enabled, the end region length is allowed to be 0%.

Cantilever span settings are applied to all spans with cantilever selected.


Continuous span settings apply to all other spans.


Standard Pattern of Bottom Reinforcement - Precast Bottom 1

Pinned span settings are applied to all spans with Fixity end 1 and 2 set to Pin.


Note: As shown above, the concept of continuity bars in pinned spans can be catered for by enabling Bar (14).

Cantilever span settings are applied to all spans with cantilever selected.


Continuous span settings apply to all other spans.

Design sections

An individual design section is created for each length of beam with similar reinforcement definitions. Each design section is then designed for the maximum forces in that region of similar reinforcement.

The numbers of design sections and their locations are determined by aggregating the different regions specified in the Design Settings> Precast> Beam: Top Longitudinal Bar Pattern, Bottom Longitudinal Bar Pattern and Link Settings.

Example: The default Precast Top 1 and Precast Bottom 1 longitudinal bar patterns for a Pinned Span are adopted without any continuity bars added as follows:

  • Precast Top 1: single region 100% of the beam span.

  • Precast Bottom 1: B1 and B3 regions set as 15% of the beam span.

  • Default Link Settings are also adopted: S1 and S3 regions set as 25% of the beam span.

For a pinned single span precast beam, different region boundaries would therefore exist at 15%, 25%, 75% and 85% of the span.

Consequently, when the span is designed in Tekla Tedds, 5 design sections would be created:

  • s1 - positioned half way along the first bottom span region (7.5% of the span)
  • s2 - positioned half way between the first and second region boundaries (20% of the span)
  • s3 - positioned half way along the second and third region boundaries (50% of the span)
  • s4 - positioned half way between the third and forth region boundaries (80% of the span)
  • s5 - positioned half way along the last bottom span region (92.5% of the span)
Note: In this example the first design section lies in the B1 bottom span region, so the positive design moment at s1 would be the maximum that occurs within B1; the second, third and forth design sections all lie in B2, so the positive design moment at s2, s3 and s4 would be the maximum that occurs within B2.

The engineer can of course adjust the standard bar patterns in the Tekla Structural Designer design settings to suit their requirements.

For instance, if in this example the Precast Bottom 1 pinned span pattern were to be amended so that B1 and B3 regions were set as 25% of the span; because the bottom and link regions would then coincide, region boundaries would only exist at 25% and 75% of the span.

Consequently, when the span is designed in Tekla Tedds, only 3 design sections would be required:

  • s1 - positioned half way along the first region (12.5% of the span)
  • s2 - positioned half way between the first and second region boundaries (50% of the span)
  • s3 - positioned half way along the last region (75% of the span)
Note: In the above elevation diagrams:
  • A black section mark indicates the selected design section is passing the design criteria.
  • Grey section marks indicate unselected design sections which are passing.
  • A red section mark would indicate a design section which is failing.

Default reinforcement in the Tekla Tedds calculation

Regardless of beam shape and size imported from Tekla Structural Designer, the reinforcement in each beam member is always defaulted to the same values Tekla Tedds calculation.

This default reinforcement is:
  • Top: 2x 16 dia bars
  • Bottom: 3x 16 dia bars
  • Shear: 2 legs of 8 dia bars at 250 cross centres


Note: The Tekla Tedds calculation contains some limitations to the error trapping when it comes to maximum reinforcement values. Although the main bars in both the top and bottom of the beam have a check allocated to prevent unrealistic distances being entered, the shear links have no such limitation.

The engineer is expected to use their own knowledge to place in shear link values and distances which are both realistic and constructible.

Note: The Tekla Tedds calculation contains some limitations to the section diagram. It may be noted that the diagram is never altered if the number of shear legs is increased from the default value of 2 legs. It should be noted that shear link legs are indicative only within Tekla Tedds and in reality there are a variety of ways that reinforcement can be detailed. The Tekla Tedds calculation therefore chooses to omit additional shear reinforcement in the section diagram and to flag it instead in the notes and the calculations.

Lifting checks

Lifting checks are disabled by default. This has been done to ensure a rapid design of grouped beams can take place. If lifting checks are required then simply enable the switch within the Design Options dialog within the Tekla Tedds calculation.

Note: The lifting check for beam members makes allowance for reinforcement for both bending and shear checks.

Analysis forces transferred from Tekla Structural Designer

The following values in the Tekla Tedds calculation are populated from the Tekla Structural Designer model.

  • Positive moment
    • Positive design moment
    • Positive quasi-permanent moment
    • Redistribution ratio
  • Negative moment
    • Positive design moment
    • Negative quasi-permanent moment
    • Redistribution ratio
  • Shear
    • Maximum Design shear force
    • Design shear force
  • Torsion
    • Design torsional moment
Note: Minor axis forces (as defined in Design > Settings > Design Forces) are not used in the design of the member. Where minor axis forces are present within a beam, a warning is displayed within the process dialog of Tekla Structural Designer.

Other precast beam properties

The following properties which are common to both cast-in-place and precast beams, are not transferred to the Tekla Tedds calculation, but still require consideration as they will impact the analysis in Tekla Structural Designer.

Content rating: 
No votes yet