Design of steel members and concrete members/walls
All steel members and/or concrete members and walls in the model can be designed by selecting an appropriate design command from the Design ribbon.
Overview
After creating and loading a model, you can proceed directly to a static design to rapidly design all steel members and all concrete members/walls for active gravity, static, ELF seismic and staged construction combinations. Any analysis that is required is automatically performed as part of the batch design process.
For larger steel models you might potentially find it more efficient to adopt a two step process consisting of a gravity design followed by a static design.
Before commencing the design you should ensure that members have their Autodesign property set appropriately. You should then also take some time to ensure Design settings are set as required.
If you have set up RSA load combinations via the Seismic Wizard these are catered for by running an RSA design.
Additional requirements may be necessary if designing members and walls for the results of a seismic analysis. For details see Seismic design methods in the Seismic analysis and design handbook
If working to the US regional code you should be aware of additional considerations in relation to The Direct Analysis Method.
If working to either the Eurocode, US, or India regional code, you may also want to introduce more/less conservatism to the design process by specifying user defined utilization ratios.
Note: As an alternative to combined
analysis and member design, you may prefer to concentrate on the design of
specific members only. To do this you would first run an analysis (e.g. Analyze All (Static) or
3D only (Static)) to
generate an appropriate set of design forces, after which you could then selectively check, or
selectively design just
those members you are interested in.
Gravity Design
Gravity Design uses the results from a 3D analysis to design* every steel and concrete member and wall in the model for all active gravity combinations. (For steel and composite members, this includes both “gravity only” and “gravity and lateral” members).
The 3D analysis can be either first or second order, depending on the settings specified on the Analysis page in Design Settings.
Note: If working to the US regional code and applying the The Direct Analysis Method refer to the suggested workflow for guidance on setting the analysis type
appropriately.
Although your final design should consider all combinations, designing for gravity combinations only can be a useful way to rapidly pre-size the members in the model that are not subjected to lateral loads.
Because you may not have created lateral systems at this stage, the column nodes that are not in a rigid floor diaphragm are, by default, fixed horizontally. To change the default setting for this go to the General page in Design Settings.
Once members have been sized acceptably for gravity combinations, a Static Design can then be run to design the remaining combinations.
* Each member is either designed or checked according to its individual Autodesign setting.
Gravity Design Process
The processes performed when a Gravity design is run can be summarized as follows:
| Process | Description |
|---|---|
| Model validation | Model validation checks are performed to detect specific issues before the analysis and design 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:
|
| Member Design | Members are designed in accordance with the
selected gravity design command:
|
| 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 |
Static Design
Static Design uses the results from a 3D analysis to design* every steel and concrete member and wall in the model for all active gravity, lateral and ELF seismic combinations. The 3D analysis can be either first or second order, depending on the settings specified on the Analysis page in Design Settings.
Note: If working to the US regional code and applying the The Direct Analysis Method refer to the suggested workflow for guidance on setting the analysis type
appropriately.
If the model contains concrete members the results from Grillage and FE chasedown analyses are also used to establish a second and third set of design forces for those members. FE chasedown results are only generated if the model contains FE meshed slabs.
You can use Design Settings to turn off 'Design for FE Chasedown analysis results' for a specific concrete member type if required. This option is located under Concrete > Cast-in-place, then Beam, Column, or Wall > General Parameters as appropriate.
Members are designed for the appropriate design requirements as follows:
- “gravity only” members for all active gravity combinations, (For more information, see Design individual members for gravity only)
- other members and walls for all active gravity, lateral and seismic combinations,
- any members or walls defined as being in Seismic Load Resisting Frames, that are subject to seismic combinations (as opposed to seismic RSA combinations) and that meet the relevant criteria for the appropriate seismic provisions.
* Each member is either designed or checked according to its individual Autodesign setting.
Note: Additional considerations may be
necessary when designing members and walls for seismic analysis. For further
details, see Seismic design methods in the Seismic analysis and design
handbook.
Static Design Process
The main steps in the Static Design process are summarized below:
| Process | Description |
|---|---|
| Model validation | Model validation checks are performed to detect specific issues before the analysis and design 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 FE and grillage chasedown analyses |
| Grillage chasedown | A Grillage chasedown analysis is only performed if required, see FE and grillage chasedown analyses |
| Member Design | Members are designed in accordance with the
selected static design command:
|
| 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 Design
RSA Design is used to design* any members defined as being in Seismic Load Resisting Frames, that are subject to seismic RSA combinations.
RSA load combinations must be set up in advance of RSA Design by running the Seismic Wizard (choosing the option to use Modal Response Spectrum Analysis).
Note: Additional considerations may be
necessary when designing members and walls for seismic analysis, see Seismic design methods in the Seismic analysis and design
handbook.
* Each member is either designed or checked according to its individual Autodesign setting.
Choice of Design Steel, Design Concrete, or Design All
The appropriate design command depends on the materials you have used in the model.
In simple terms:
-
If your model consists of steel members only, you can run the design by using the Design Steel commands.
-
If your model consists of concrete members only, you can run the design by using the Design Concrete commands.
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If your model consists of a mix of both concrete and steel members, you can run the design by using the Design All commands.
Tip: For structures that are mostly
steel but have a few concrete members - instead of running Design All, you could run
Design Steel (in order to focus on the steel design) before switching to Design
Concrete for the remaining members.
In this way during the steel design phase you are not running grillage and FE chasedown analyses when they are not required .
For more details on how each command affects the analysis process, see the following.
Design steel
-
Performs a 3D analysis, and/or a staged construction analysis.
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Does not perform grillage chasedown or FE chasedown analysis.
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Designs or checks all steel elements.
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Does not design or check concrete beams, columns or shear walls.
Design concrete
-
Performs a 3D analysis and/or a staged construction analysis, and a grillage chasedown analysis.
-
May also be required to perform an FE chasedown analysis.
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Designs or checks all concrete beams, columns and shear walls.
-
Does not design or check steel elements.
Design all
-
Performs a 3D analysis and/or staged construction analysis, and a grillage chasedown analysis.
-
May also be required to perform an FE chasedown analysis.
-
Designs or checks all concrete beams, columns and shear walls.
-
Designs or checks all steel elements.
Design force sets used for steel and concrete member design
The analysis results that are used to generate design force sets are configured on the Analysis page in Design Settings.
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Firstly, you need to select whether the analysis should be first-order or second-order. The chosen setting gets applied to 3D building analysis and/or staged construction analysis.
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Next you need to decide whether to include staged construction analysis.
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If you have included staged construction analysis, (as shown below) you can then select which other results should also be considered in the design.
Having made your selections the design force sets used are as follows.
Steel Member Design Forces
First-order or second-order 3D analysis, and/or staged construction analysis are the only results used to generate design force sets for steel member design.
Concrete Member Design Forces
The number of design force sets used for concrete member design will depend on whether staged construction analysis results have been included.
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If staged construction analysis results have not been included, up to three sets of design forces will be available:
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3D analysis results will always be used to design all beams, columns and walls.
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Grillage chasedown results will exist for gravity loadcases if the model contains any concrete beams, in which case they will also be used to design all beams, columns and walls.
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FE chasedown results for gravity loadcases will also exist if the model contains 2-way spanning slabs. These results will be used (if selected), to design all beams, columns and walls*.
-
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If staged construction analysis results have been included, up to four sets of design forces will be available:
-
Staged construction analysis results will always be used to design all beams, columns and walls
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3D analysis results will be used (if selected), to design all beams, columns and walls
-
Grillage chasedown results will exist for gravity loadcases if the model contains any concrete beams, in which case they will also be used (if selected), to design all beams, columns and walls.
-
FE chasedown results for gravity loadcases will also exist if the model contains 2-way spanning slabs. These results will be used (if selected), to design all beams, columns and walls*.
-
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).