Using the Eurocode EN1998-1:2004 seismic wizard
The Seismic Wizard guides you through the process of defining the information that is required in order to calculate the seismic loading on the structure.
This section runs through each page of the wizard and discusses the various options.
Starting the Wizard
To initiate the wizard:
- Click Load > Seismic Wizard...
The Seismic Wizard will start, and you can use its pages to define the necessary information. The first page displayed is Site Specific Spectra.
Site Specific Spectra page
You can choose the analysis procedure to be used, either:
| Property | Description |
|---|---|
| Code Spectra | Choose this option to use the EN 1998-1 Horizontal Design Spectrum. |
| Site Specific Spectra | This option is appropriate for locations which use another
country's loading and design codes where the code spectrum is not
relevant. For this option you create a user defined spectrum by specifying the required curve parameters and slope options. |
| Next |
Clicking Next takes you to the Basic information page described below. |
Note:
No vertical spectrum is considered in the current release.
Basic information page
| Property | Description |
|---|---|
| Structure details | |
| Height to the highest level | This field defaults to the structure height (calculated from the base to the highest point on the structure). |
| Ignore seismic in floor (and below) | Only floors above this level are considered when the seismic inertia combination is determined. |
| Number of storeys | This field defaults to the number of ticked floors in the Construction levels dialog less the ones ignored in field above. |
| Ground acceleration | |
| Region | Only applies for the Malaysia NA:
|
| Reference Peak Ground Acc, agR | Refer to PD6698:2009 |
| Design Ground Acc, ag | agR x γI. |
| Importance & Ground | |
| Importance class | For Base Eurocode and UK NA: I- IV as defined in BS EN
1998-1:2004 - Table 4.3. For Singapore NA: Ordinary or Special |
| Ground type | For Base Eurocode and UK NA: A-E For Malaysia NA: Rock, Stiff Soil, Flexible Soil For Singapore NA: C, D, S1 (A - Rock, B - Very dense soil/gravel/clay, C - Deposits of dense/medium dense soil, D - Loose to medium soil, E - Surface alluvium. Ref BS EN 1998-1:2004 - Table 3.1.) |
| Importance Factor, γI | This is automatically derived from the occupancy class. |
| Spectrum type |
For Base Eurocode and UK NA: Spectrum Type - 1 or 2 BS EN 1998-1:2004 - Cl 3.2.2.2.1(P) For Malaysia NA: Spectrum Type - 1 For Singapore and Norway NA: (No choice) |
| Lower bound factor, β |
This is automatically derived. |
| Upper limit of the period of the constant spectral acceleration branch, Tc |
This is automatically derived. |
| Structural Ductility Class |
Low, Medium or High - for whole building (not directional) If ag ≤ 0.78 m/s2 or if ag x S ≤ 0.98 m/s2 - Structure suitable for Low Seismicity (where S is the soil factor) If not - Structure suitable for Medium or High Seismicity |
| Site natural period, TS (Malaysia NA only) |
This is only required if the ground type is Flexible Soil. |
| Elastic response spectral displacement, SDR (Malaysia NA only) |
This is only required if the ground type is Flexible Soil. |
| Next | Clicking Next takes you to the Structure regularity page described below. |
Note:
The Norway NA for EC1998 has the following differences:-
Soil factors specific to Norway
- φ factor for Imposed load types A, B and C = 1.0 (not 0.8)
- γI importance factors specific to Norway- Spectrum specific to Norway (TB, TC and TD factors)
- q values for Ductility Class Medium use for both Medium and High
Structure regularity page
For Medium and High structural ductility this page is used to indicate any irregularities in plan or elevation. (For Low structural ductility only the irregularities in elevation are displayed.)
| Property | Description |
|---|---|
| Structure Plan Regularity - Cl 4.2.3.2 | Check the appropriate boxes to define any plan irregularities. |
| Structure Elevation Regularity - Cl 4.2.3.3 | Check the appropriate boxes to define any elevation irregularities. |
| Analysis procedure to be used | Having specified any irregularities, you then choose the
analysis procedure.
Note: Based on
the irregularities you have defined, one or both of the above
methods may be unavailable. Any additional information, assumptions or warnings applicable to the selected a method are displayed for information. |
| Next | Clicking Next takes you to the Fundamental Period page described below. |
Fundamental Period page
This page is used to determine the fundamental period, TDir 1 and TDir 2
| Property | Description |
|---|---|
| Fundamental Period Definition | |
| Use approx fundamental period TA | If RSA was selected on the previous page this option is dimmed. |
| User defined fundamental period | If RSA was selected on the previous page this option is dimmed. |
| Use modal analysis | Modal analysis is run to determine fundamental periods of the structure in Dir1 and Dir2. |
| Fundamental Period Dir 1 and Dir 2 | |
| Structure Type |
Select from Moment resistant space steel frames, Moment resistant space concrete frames, Eccentrically braced steel frames, All other structures (ref BS EN 1998-1 Cl 4.3.3.2.2) |
| Approx fundamental period, TA |
This is automatically derived. |
| Fundamental period, TDir 1, TDir 2 |
Depending on your choice of definition this will either be taken as TA, or it can be a user defined value, or it will be calculated from the modal analysis. |
| Next | Clicking Next takes you to the Behaviour Factor page described below. |
Behaviour Factor page
For Low Ductility Class, q = 1.5, (but the value can be changed by the user) - all other fields on the page are dimmed and cannot be changed.
For Medium or High Ductility Classes, this page is used to determine the Behaviour Factor in direction 1 and 2.
| Property | Description |
|---|---|
| Ductility Class | Medium or High. |
| Structure Type | Moment resistant space steel frames, Moment resistant space concrete frames, Eccentrically braced steel frames, All other structures |
| Frame Type | This options displayed here depend on the structure type selected above. |
| αu/ αl | This is a user defined multiplication factor - for the structure |
| User defined q | For Medium or High Ductility Classes, select this checkbox in order to edit the calculated q value. |
| Behaviour Factor, q | This is automatically derived, but you are given the facility to edit the calculated value. |
| Next | Clicking Next takes you to the Seismic Inertia Combination page described below. |
Seismic Inertia Combination page
This page is used to set up the loadcases for the Seismic Inertia combination.
You should include those loadcases that you want to contribute to the effective seismic weight of the structure.
Note: The Seismic Inertia combination is used to
develop the seismic design loading and is classed as a modal mass combination for
the modal analysis. It is not used in any other analysis of the structure.
Clicking Next takes you to the Localization page described below.
Localization page
On this page you can:
- choose whether to perform seismic drift checks, and set the allowable story drift factor to be used
- define appropriate localization parameters
| Property | Description |
|---|---|
| Skip seismic drift checks - Check this box if you do not require seismic drift checks to be performed. | |
| Structure Type | Select the structure type for determining the allowable story drift factor. |
| Importance Class | Displays the risk category that was selected on an earlier page of the wizard. |
| Allowable Story Drift Factor | The factor to be used when calculating the allowable story drift is determined from the above two parameters. Click 'override' if you want to enter your own value. |
| - | |
| ELF & RSA | |
| Scale Factor between elastic and design spectra (Dir1 and Dir2) | This field allows you to override the code value for the scale factor, (Eurocode value = 1/q ). |
| Design Static Base Shear, V (Dir1 and Dir2) | This field allows you to override the code value for the static base shear, (Eurocode value FB = Sd (Tl) x m x λ). |
| % eccentricity for accidental torsion (Dir1 and Dir2) | This field allows you to override the code eccentricity for
accidental torsion, (Eurocode value = 5%). Note: The same value is
applied to all floors in the structure. |
| Vertical seismic load effect combination factor | This field allows you to override the combination factor for vertical seismic loading (usually a small additional factor for the dead loads in the combination),( (Eurocode - No vertical loads considered - factor = 0.0). |
| RSA only | (only available if RSA has been selected) |
| % Mass participation for RSA | This field allows you to set your own required % mass
participation, (Eurocode value = 90%). Note: This overrides the
setting in Analysis Options/1st order seismic when running the
Seismic Wizard. Note: It is not usually
possible to achieve 100% mass participation in a modal analysis so
max value is 99%. Note: This setting can
benefit some users wanting nearer 100% to be conservative.
|
| Scaling of forces (% of Base Shear) (Dir1 and Dir2) | This field allows you to set your required scaling factors, (Eurocode - No base shear adjustment). |
| Scaling of Deflections for Drift Checks (% of Base Shear) (Dir1 and Dir2) | This field allows you to set your required scaling factors,
(Eurocode - No adjustment). Note: A zero factor means
no scaling will be performed on deflections. |
| Finish | Click Finish to automatically generate the Seismic loadcases and open the EC8 Seismic Combination Generator described below. |
EC8 Seismic Combination Generator
The Combination Generator uses the two “core” combinations from EC8 that include seismic loads as below:
Equation 6.12a
Gkj + AEd + ψ2,i x Qk,i
Equation 6.12b
Gkj + AEd
Provided the generate option is selected these will then be used, with factors as specified, to generate an appropriate number of combinations to cover for direction +/- Dir1 and Dir2 with +/- eccentricities.
| Property | Description |
|---|---|
| Initial Parameters page | |
| Delete / Replace combinations | Select whether to:
|
| Scenario | If you need to generate combinations for a range of different scenarios, ensure you type in (or choose from the droplist if appropriate) a scenario name. This scenario name is then added as a prefix to all the combinations generated in the this run of the generator. You can then rerun the generator to create additional scenarios. |
| Clicking Next takes you to the Combinations page described below. | |
| Combinations page | |
| Generate | Select the seismic combinations to be generated with factors as specified. |
| Keep existing Seismic Combinations | If you want to retain previously set up Seismic Combinations you
can select this checkbox to do so. Note: Warning - some
factors may no longer be correct for these combinations after
rerunning the Wizard. |
| Next | Click Next to specify the service combinations. |
| Finish | Click Finish to generate the Seismic combinations. |