Analysis types and settings
Typically the static analysis types considered for building design in Tekla Structural Designer will be a 3D building analysis or staged construction analysis, and potentially also a grillage chasedown and/or FE chasedown.
3D building analysis or staged construction analysis can be first-order or second-order and can be either linear or non-linear.
First and second-order RSA seismic analyses are provided to cater for RSA seismic analysis and design.
Other analysis types available include first-order modal analysis and second-order buckling analysis.
All of the above analyses are run from the Analyze ribbon.
Various default parameters for controlling the analysis can be edited if required via Analysis settings.
Before running an analysis you should familiarize yourself with the analysis limitations and assumptions.
Note that two further analysis processes are available which are not accessed from the Analyze ribbon.
- An iterative cracked section analysis for calculating slab deflections - this is run from the Slab Deflection ribbon.
- A footfall analysis for assessing human induced vibrations on floors - this is run from the Footfall Analysis ribbon, which is displayed when you work in a Footfall Analysis View regime.
An overview of each of the different analysis types is given in the sections below:
3D building analysis - 1st/2nd order, linear/non-linear
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.
Nonlinearity Included:
- Geometric: No
- Material: No
The processes performed when this analysis type is run can be summarized as follows:
| Process | Description |
|---|---|
| Model validation | Model validation checks are performed if required 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:
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 solver model. |
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.
Nonlinearity Included:
- Geometric: No
- Material: Yes
The processes performed when this analysis type is run can be summarized as follows:
| Process | Description |
|---|---|
| Model validation | Model validation checks are performed if required 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 solver model. |
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.
Nonlinearity Included:
- Geometric: Yes
- Material: No
The processes performed when this analysis type is run can be summarized as follows:
| Process | Description |
|---|---|
| Model validation | Model validation checks are performed if required 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:
The actual pre-analysis processes performed will vary depending on the specific model that has been defined. |
| 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 solver model. |
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.
Nonlinearity Included:
- Geometric: Yes
- Material: Yes
The processes performed when this analysis type is run can be summarized as follows:
| Process | Description |
|---|---|
| Model validation | Model validation checks are performed if required 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:
The actual pre-analysis processes performed will vary depending on the specific model that has been defined. |
| 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 solver model. |
Staged construction analysis - 1st/2nd order, linear/non-linear
Note:
For further information about designing your building utilizing this type of analysis, see the Staged construction handbook
1st order linear SCA
1st order linear static staged construction analysis can only be run if a "Staged Construction" class of combination has been defined. This type of analysis is suitable for structures where secondary effects are negligible. Any nonlinear springs or nonlinear elements present are constrained to act linearly.
Nonlinearity Included:
- Geometric: No
- Material: No
The processes performed when this analysis type is run can be summarized as follows:
| Process | Description |
|---|---|
| Model validation | Model validation checks are performed if required 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:
The actual pre-analysis processes performed will vary depending on the specific model that has been defined. |
| 3D analysis:First order linear |
A traditional frame first-order linear analysis of the entire 3D model. |
| 3D analysis:First-order linear staged construction |
A first-order linear staged construction analysis of the entire 3D model for the staged construction combination and other combinations. |
1st order non-linear SCA
1st order non-linear static staged construction analysis can only be run if a "Staged Construction" class of combination has been defined.
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.
Nonlinearity Included:
- Geometric: No
- Material: Yes
The processes performed when this analysis type is run can be summarized as follows:
| Process | Description |
|---|---|
| Model validation | Model validation checks are performed if required 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:
The actual pre-analysis processes performed will vary depending on the specific model that has been defined. |
| 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 staged construction |
A first-order non-linear staged construction analysis of the entire 3D model for the staged construction combination and other combinations. |
2nd order linear SCA
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.
Nonlinearity Included:
- Geometric: Yes
- Material: No
The processes performed when this analysis type is run can be summarized as follows:
| Process | Description |
|---|---|
| Model validation | Model validation checks are performed if required 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:
The actual pre-analysis processes performed will vary depending on the specific model that has been defined. |
| 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 staged construction |
A 2nd order linear staged construction analysis of the entire 3D model for the staged construction combination and other combinations. |
2nd order non-linear SCA
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.
Nonlinearity Included:
- Geometric: Yes
- Material: Yes
The processes performed when this analysis type is run can be summarized as follows:
| Process | Description |
|---|---|
| Model validation | Model validation checks are performed if required 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:
The actual pre-analysis processes performed will vary depending on the specific model that has been defined. |
| 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 staged construction |
A 2nd order non-linear staged construction analysis of the entire 3D model for the staged construction combination and other combinations. |
FE and grillage chasedown analyses
Note:
You can learn more about chasedown analysis by working through the Background to the Analysis/Design procedures eLearning.
We know from experience that a 3D building 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 an FE and/or grillage chasedown is used to emulate traditional analysis and establish alternative set(s) of design forces.
Chasedown analyses cannot be run in isolation, they are only performed when required as part of the following batch analysis, or batch analysis and design, processes:
- Analyze All (Static)
- Design Steel (Gravity)
- Design Steel (Static)
- Design Concrete (Gravity)
- Design Concrete (Static)
- Design All (Gravity)
- Design All (Static)
FE chasedown
An FE chasedown is only required if the model contains meshed slabs, (these can be either two-way spanning slabs, or one-way spanning slabs with the "Analyze slab" property selected).
| 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 considered for timber member design and slab design. They can also optionally be used for: steel member design; concrete beam, concrete column and concrete wall design. Note: You
can use Design Settings to turn
off 'Design for FE Chasedown analysis results' for steel
members and concrete members/walls if required. For
steel this option is located under Design Settings > Steel > General. For
concrete 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.
Grillage chasedown
Grillage chasedown is used to emulate a traditional analysis and establish an alternative second set of design forces for concrete beams, columns and walls.
It is only performed if the model contains concrete beams, columns, or walls, or if it has been requested for steel member design.
| 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 Note: You
can use the options located under Design Settings > Steel > General to turn
off 'Grillage Chasedown' for steel members.
|
Features of 3D building and chasedown analyses
The following table compares the features of the three analysis types that can be used to generate sets of forces suitable for static design.
Note: In the table the term '3D Building
Analysis' refers to any of 1st-order linear, 1st order non-linear, 2nd order
linear, 2nd order non-linear analysis types.
| Feature | 3D Building Analysis | Grillage Chasedown | FE Chasedown |
|---|---|---|---|
| Examples / When useful? | Gravity and Lateral analysis (Notional/Wind/Seismic) | “Beam & Slab” buildings | Flat slab and “Beam & Slab” buildings |
| Special Features |
|
|
|
| Benefits |
|
Member design based on traditional sub frame is considered simultaneously with that for 3D Analysis |
|
| Analysis Model |
3D model of entire building:
|
series of 3D sub models:
|
series of 3D sub models:
|
| Analysis Method | Whole model in one pass | Each sub model sequentially from top to bottom – chasing member loads down | Each sub model sequentially from top to bottom – chasing member loads down |
| Analysis Type |
|
First order | First order |
| Supports | External supports as defined by the user | Ends of members above/below each sub model are automatically supported | Ends of members above/below each sub model are automatically supported |
| Loading | Gravity and Lateral Loads | Gravity Loads only | Gravity Loads only |
| Forces for design | |||
| RC Slab | Yes– All Combs | No forces | Yes – All Gravity loadcases are replaced in Combs* |
| RC Beam | Yes– All Combs | Yes – All Gravity loadcases are replaced in Combs* | Optional – All Gravity loadcases are replaced in Combs* |
| RC Column | Yes– All Combs | Yes – All Gravity loadcases are replaced in Combs* | Optional – All Gravity loadcases are replaced in Combs* |
| RC Wall | Yes– All Combs | Yes – All Gravity loadcases are replaced in Combs* | Optional – All Gravity loadcases are replaced in Combs* |
| Steel/Composite Members | Yes – All Combs except patterns | Not required | Not required |
| Timber Members (via Tedds) | Yes | Yes | Yes |
| Foundation design | Yes – All Combs except patterns | Yes – All Gravity loadcases are replaced in Combs* | Yes – All Gravity loadcases are replaced in Combs* |
* - see "Accounting for lateral loading in chasedown results" below.
Accounting for lateral loading in chasedown results
It is important to note that the chasedown analysis procedures are 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:
- Start with the 3D building analysis combination result
- Identify all gravity cases used in the combination and the relevant load factor
- For each included gravity
loadcase:
- Subtract the 1st order linear building analysis result multiplied by the relevant load factor
- Add the chasedown result multiplied by the relevant load factor
- 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: The above 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.
Analyze All (Static)
Analyze All (Static) is a batch process that includes the full series of analyses required to enable a static design to be performed.
While these analyses are performed automatically as required whenever a combined analysis and design process is initiated from the Design ribbon, this option has been provided on the Analyze ribbon so that you can run these analyses without having to complete the entire design process before you can access the analysis results.
- 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 if required 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:
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:
|
| 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 |
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 if required 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:
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:
|
| 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 |
RSA seismic analysis
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
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
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.
1st order modal analysis
Note:
For further details about this type of analysis, see Modal analysis
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.
Nonlinearity Included:
- Geometric: No
- Material: No
The processes performed when this analysis type is run can be summarized as follows:
| Process | Description |
|---|---|
| Model validation | Model validation checks are performed if required 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:
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 solver model. |
2nd order buckling analysis
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.
Nonlinearity Included:
- Geometric: Yes
- Material: No
The processes performed when this analysis type is run can be summarized as follows:
| Process | Description |
|---|---|
| Model validation | Model validation checks are performed if required 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:
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 solver model. |
Rigorous slab deflection analysis
Note:
For further information about this type of analysis, see the Slab deflections handbook
Tekla Structural Designer's rigorous slab deflection analysis provides a rigorous approach to slab deflection estimation. It comprises
- (i) Sequential Loading Analysis,
- (ii) iterative cracked section analysis, and
- (iii) simple modeling of creep and shrinkage effects.
Footfall Analysis
Note:
For further information about this type of analysis, see the Footfall assessment handbook
Tekla Structural Designer's footfall analysis provides an accurate method for assessing human induced vibrations on floors.
This involves the creation and modal analysis of floor analysis models for dedicated footfall mass combinations.
The resulting workflow consists of two parts:
- (i) Prediction of the structural response in terms of acceleration and/or velocity.
- (ii) Footfall checks to evaluate the limiting criteria.
The approach can be performed to either the SCI P354, CCIP-016 or AISC DG11 design guide.