Analysis types in Tekla Structural Designer

Tekla Structural Designer
2021
Tekla Structural Designer

Analysis types in Tekla Structural Designer

Note: Before running analysis you should familiarize yourself with the analysis limitations and assumptions.

The following analysis types can be run in Tekla Structural Designer:

1st order linear

1st order linear static analysis is suitable for structures where secondary effects are negligible. Any nonlinear springs or nonlinear elements present are constrained to act linearly.

Loadcases and Combinations to be considered in the analysis can be pre-selected.

The processes performed when this analysis type is run can be summarized as follows:

Process Description
Model validation Model validation checks are performed to detect specific issues before the analysis process begins.
3D pre-analysis processes In preparation for analysis a number of pre-analysis processes are undertaken as necessary, such as:
  • Decomposing slab and wall loads
  • Preparing loadcases and combinations
  • Meshing and diaphragms
  • Applying loads
  • Resolving vertical loads for application of global imperfections

The actual pre-analysis processes performed will vary depending on the specific model that has been defined.

3D analysis

A traditional frame first-order linear analysis of the entire 3D model.

Nonlinearity Included:

  • Geometric: No
  • Material: No

Related concept: Features of 3D analysis and chasedown analysis

Related task: Run 1st order linear analysis

1st order non-linear

This is a nonlinear analysis with loading applied in a single step.

It is suitable for structures where secondary effects are negligible and nonlinear springs/elements are present.

Loadcases and Combinations to be considered in the analysis can be pre-selected.

The processes performed when this analysis type is run can be summarized as follows:

Process Description
Model validation Model validation checks are performed to detect specific issues before the analysis process begins.
3D analysis: First-order linear A 1st order linear analysis (see above), is automatically performed prior to the non-linear analysis.
3D analysis: First-order non-linear

A traditional frame first-order non-linear analysis of the entire 3D model, with an option to mesh floors.

Nonlinearity Included:

  • Geometric: No
  • Material: Yes

Related concept: Features of 3D analysis and chasedown analysis

Related task: Run a 1st order non-linear analysis

1st order modal

This is an unstressed modal analysis which can be used to determine the structure's natural frequencies.

The structure is assumed to be in an unstressed state and nonlinear elements are constrained to act linearly.

The processes performed when this analysis type is run can be summarized as follows:

Process Description
Model validation Model validation checks are performed to detect specific issues before the analysis process begins.
3D pre-analysis processes In preparation for analysis a number of pre-analysis processes are undertaken as necessary, such as:
  • Decomposing slab and wall loads
  • Preparing loadcases and combinations
  • Meshing and diaphragms
  • Applying loads

The actual pre-analysis processes performed will vary depending on the specific model that has been defined.

3D analysis First-order Modal

A first-order modal analysis of the entire 3D model, with an option to mesh floors.

Nonlinearity Included:

  • Geometric: No
  • Material: No

Related concept: Features of modal analysis

Related task: Run a 1st order modal analysis

2nd order linear

This is a 2-stage P-Delta analysis which is suitable for structures where secondary effects are of comparable magnitude to primary effects. Any nonlinear springs or nonlinear elements present are constrained to act linearly.

Loadcases and Combinations to be considered in the analysis can be pre-selected.

The processes performed when this analysis type is run can be summarized as follows:

Process Description
Model validation Model validation checks are performed to detect specific issues before the analysis process begins.
3D analysis: First-order linear A 1st order linear analysis (see above), is automatically performed prior to the 2nd order linear analysis.
3D analysis: Second-order linear

A traditional frame 2nd order linear analysis of the entire 3D model, with an option to mesh floors.

Nonlinearity Included:

  • Geometric: Yes
  • Material: No

Related concept: Features of 3D analysis and chasedown analysis

Related task: Run a 2nd order linear analysis

2nd order non-linear

This is a nonlinear analysis with loading applied in a single step.

It is suitable for structures where secondary effects are of comparable magnitude to primary effects and nonlinear springs/elements are present.

Loadcases and Combinations to be considered in the analysis can be pre-selected.

The processes performed when this analysis type is run can be summarized as follows:

Process Description
Model validation Model validation checks are performed to detect specific issues before the analysis process begins.
3D analysis: First-order linear A 1st order linear analysis (see above), is automatically performed prior to the 2nd order non-linear analysis.
3D analysis: Second-order non-linear

A traditional frame 2nd order non-linear analysis of the entire 3D model, with an option to mesh floors.

Nonlinearity Included:

  • Geometric: Yes
  • Material: Yes

Related concept: Features of 3D analysis and chasedown analysis

Related task: Run a 2nd order non-linear analysis

2nd order buckling

This is a linear buckling analysis which can be used to determine a structure's susceptibility to buckling.

The stressed state of the structure is determined from linear analysis; therefore nonlinear elements are constrained to act linearly.

Loadcases and Combinations to be considered in the analysis can be pre-selected.

The processes performed when this analysis type is run can be summarized as follows:

Process Description
Model validation Model validation checks are performed to detect specific issues before the analysis process begins.
3D pre-analysis processes In preparation for analysis a number of pre-analysis processes are undertaken as necessary, such as:
  • Decomposing slab and wall loads
  • Preparing loadcases and combinations
  • Meshing and diaphragms
  • Applying loads

The actual pre-analysis processes performed will vary depending on the specific model that has been defined.

3D analysis Second-order buckling

A second-order buckling analysis of the entire 3D model.

Nonlinearity Included:

  • Geometric: Yes
  • Material: No

Related task: Run a 2nd order buckling analysis

FE chasedown

This analysis type cannot be run in isolation, it is only performed when it is required as part of one of the following batch analysis/design processes:

  • Analyze All (Static)
  • Design Concrete (Gravity)
  • Design Concrete (Static)
  • Design All (Gravity)
  • Design All (Static)

It is only required in the above processes if the model contains meshed slabs.

Process Description
FE chasedown

Separate analyses are performed for a series of 3D sub models each containing the members between two horizontal planes with fully meshed floors. See: Solver Model used for FE Chasedown.

The complete series of models is chased down from top to bottom so loads are carried from the level above to the level below.

The results are always used for slab design and optionally used for concrete beam, column and wall design.

Note: You can use Design Settings to turn off 'Design for FE Chasedown analysis results' for concrete beams, columns or walls if required. This option is located under Concrete > Cast-in-place, then Beam/Column/Wall > General Parameters (as appropriate).

A significant consideration when opting to design for the FE chasedown results is that the slabs will tend to carry a significant proportion of the load direct to the columns.

Consequently, for beam design in particular, it is unlikely that an FE chasedown could result in a more critical set of design forces than would be already catered for by a Grillage chasedown.

Note: If duplicate levels have been specified in the Construction Levels dialog separate sub models are created and analyzed for the source and every duplicate level. This ensures that the increasing load carried by the vertical members in the lower sub models is catered for. In turn this can cause small differences in the analysis results (and consequently the design) for these sub models.

Accounting for lateral loading in chasedown results

It is important to note that the chasedown analysis procedure is only valid for gravity loads. The chasedown analysis results for any lateral loadcase (wind / EHF) or from the direct analysis of any combination that includes a lateral loadcase are not valid.

Therefore in order to generate a set of forces suitable for design, the chasedown analysis results are merged with the 3D building analysis combination results as follows:

  1. Start with the building analysis combination result
  2. Identify all gravity cases used in the combination and the relevant load factor
  3. For each included gravity loadcase:
    1. Subtract the 1st order linear building analysis result multiplied by the relevant load factor
    2. Add the chasedown result multiplied by the relevant load factor
  4. For results with live/imposed load reduction, subtract the relevant % of the chasedown result for each reducible loadcase.

Following this procedure means that chasedown analysis of lateral loadcases or combinations is not required.

Note: This procedure is only applied to beam, column, and wall-line results, but not to 2D nodal results. For this reason it is not possible to calculate or display 2D element chasedown results for combinations that include lateral loadcases.

Related concept: Features of 3D analysis and chasedown analysis

Grillage chasedown

We know from experience that a 3D Analysis on its own does not give the gravity results engineers have traditionally used or want - staged construction analysis reduces but doesn't resolve this. Therefore, in Tekla Structural Designer a grillage chasedown is used to emulate a traditional analysis and establish an alternative second set of design forces for concrete beams, columns and walls.

Grillage chasedown analysis cannot be run in isolation, it is only performed when it is required as part of the following processes:

  • Analyze All (Static)
  • Design Concrete (Gravity)
  • Design Concrete (Static)
  • Design All (Gravity)
  • Design All (Static)

In each of the above processes grillage chasedown is only performed if the model contains concrete beams, columns, or walls.

Process Description
Grillage chasedown

Separate analyses are performed for a series of 3D sub models each containing the members between two horizontal planes, floors only being meshed at those levels where they have also been meshed in 3D Analysis.

The complete series of models is chased down from top to bottom so loads are carried from the level above to the level below. See: Solver Model used for Grillage Chasedown

Accounting for lateral loading in chasedown results

It is important to note that the chasedown analysis procedure is only valid for gravity loads. The chasedown analysis results for any lateral loadcase (wind / EHF) or from the direct analysis of any combination that includes a lateral loadcase are not valid.

Therefore in order to generate a set of forces suitable for design, the chasedown analysis results are merged with the 3D building analysis combination results as follows:

  1. Start with the building analysis combination result
  2. Identify all gravity cases used in the combination and the relevant load factor
  3. For each included gravity loadcase:
    1. Subtract the 1st order linear building analysis result multiplied by the relevant load factor
    2. Add the chasedown result multiplied by the relevant load factor
  4. For results with live/imposed load reduction, subtract the relevant % of the chasedown result for each reducible loadcase.

Following this procedure means that chasedown analysis of lateral loadcases or combinations is not required.

Note: This procedure is only applied to beam, column, and wall-line results, but not to 2D nodal results. For this reason it is not possible to calculate or display 2D element chasedown results for combinations that include lateral loadcases.

Related concept: Features of 3D analysis and chasedown analysis

Analyze All (Static)

This is batch process that includes the full series of analyses required to enable a static design to be performed.

  • 3D analysis
    • 1st order linear/non-linear
    • 2nd order linear/non-linear (only if this has been specified by the user in Design > Design Settings > Analysis)
  • FE chasedown (if required)
  • Grillage chasedown (if required)

The processes performed when this analysis type is run can be summarized as follows:

Process Description
Model validation Model validation checks are performed to detect specific issues before the analysis process begins.
3D pre-analysis processes In preparation for analysis a number of pre-analysis processes are undertaken as necessary, such as:
  • Decomposing slab and wall loads
  • Preparing loadcases and combinations
  • Meshing and diaphragms
  • Applying loads
  • Resolving vertical loads for application of global imperfections

The actual pre-analysis processes performed will vary depending on the specific model that has been defined.

3D analysis

A traditional frame analysis of the entire 3D model, with an option to mesh floors. This analysis generates a first set of results that can be used for the design of beams, columns, walls and slabs.

You can control whether a first, or a second order 3D Analysis is run by making the appropriate selection on the Analysis page in Design Settings. The actual options that are presented will vary depending on the design code being worked to.

The choice of linear or non-linear analysis is made automatically:

  • if the model has entirely linear properties a linear analysis is performed,
  • else if any non-linear properties are detected a non-linear analysis is performed.
FE chasedown An FE chasedown analysis is only performed if required, (see above FE Chasedown topic) .
Grillage chasedown A Grillage chasedown analysis is only performed if required, (see above Grillage chasedown topic).
Stability checks Sway/Drift checks and Wind Drift checks are performed for all columns and walls, (apart from any that have been manually excluded from the check

Related concept: Features of 3D analysis and chasedown analysis

Related concept: Why chasedown analyses are included in Analyze All (Static)

Related task: Run Analyze All (Static)

3D only (Static)

This is a batch process similar to Analyze All (Static) but which excludes chasedowns to save time during scheme design, (for example while addressing overall stability, sway, drift, wind drift, etc.)

The processes performed when this analysis type is run can be summarized as follows:

Process Description
Model validation Model validation checks are performed to detect specific issues before the analysis process begins.
3D pre-analysis processes In preparation for analysis a number of pre-analysis processes are undertaken as necessary, such as:
  • Decomposing slab and wall loads
  • Preparing loadcases and combinations
  • Meshing and diaphragms
  • Applying loads
  • Resolving vertical loads for application of global imperfections

The actual pre-analysis processes performed will vary depending on the specific model that has been defined.

3D analysis

A traditional frame analysis of the entire 3D model, with an option to mesh floors. This analysis generates a first set of results that can be used for the design of beams, columns, walls and slabs.

You can control whether a first, or a second order 3D Analysis is run by making the appropriate selection on the Analysis page in Design Settings. The actual options that are presented will vary depending on the design code being worked to.

The choice of linear or non-linear analysis is made automatically:

  • if the model has entirely linear properties a linear analysis is performed,
  • else if any non-linear properties are detected a non-linear analysis is performed.
Stability checks Sway/Drift checks and Wind Drift checks are performed for all columns and walls, (apart from any that have been manually excluded from the check

Related task: Run 3D only (Static)

1st order RSA seismic

This is a Modal Response Spectrum Analysis used to determine the peak response of the structure to earthquakes. Any nonlinear springs or nonlinear elements present are constrained to act linearly. For RSA Seismic Combinations, the peak responses are enveloped around the static results for 1st Order Linear Analysis

Related task: Run a 1st order RSA seismic analysis

2nd order RSA seismic

This is a Modal Response Spectrum Analysis used to determine the peak response of the structure to earthquakes. Any nonlinear springs or nonlinear elements present are constrained to act linearly. For RSA Seismic Combinations, the peak responses are enveloped around the static results for 2nd Order Linear Analysis

Related task: Run a 2nd order RSA seismic analysis

Analyze All (RSA)

This is the same Modal Response Spectrum Analysis that would be carried out as part of Design All (RSA), but with no design. Any nonlinear springs or nonlinear elements present are constrained to act linearly.

Related task: Run Analyze All (RSA)

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