Using the ASCE 7 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 ASCE 7 Horizontal Design Spectrum. |
| Site Specific Spectra (user defined - based on Sd and T) | User defined spectra are 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. |
| Site Specific Spectra (user defined - generic curve) | User defined spectra are 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 manually, or by pasting data from a spreadsheet. Note: The
spreadsheet data must be in the form of period vs acceleration
values and in ascending order of period (the input dialog features
an automatic Sort command if the latter is not the case). |
| 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
The Seismic Design Category (SDC) is determined on this page.
Note:
In ASCE 7-10 (not ASCE 7-05) there is an additional value of Cs calculated for a building < 5 stories and where T <0.5s. In this instance Ss is taken as 1.5 and the additional value of Cs should be used to give a final value of Cs. This clause has not been implemented in Tekla Structural Designer.
| 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 weight combination is determined. |
| Number of stories | This field defaults to the number of ticked floors in the Construction levels dialog less the ones ignored in field above. |
| Site Occupancy | |
| Site class | This field allows you to set the appropriate soil conditions, A-E - (A - Hard rock, B - Rock, C - Very dense soil/soft rock, D - Stiff soil, E - Soft soil. as defined in ASCE 7-05 & ASCE-10 Table 20.3-1. |
| Occupancy/Risk Category | This field allows you to set the appropriate occupancy category, I-IV, as defined in ASCE 7-05 &-10 Table 1-1. |
| Importance Factor, Ie | This is automatically derived from the occupancy class. |
| Override checkbox | Checking this box allows you to override the importance factor, (some countries require different Importance Factors to those given in the US codes). |
| Seismic Design Category (SDC) | |
| Seismic Design Category (SDC) | User editable (range A-F) |
| Alternative seismic design category determination | Select this checkbox in order to use the alternative determination from IBC2009 1613.5.6.1 / IBC2012 1613.5.6. |
| User Defined SDC | Select this checkbox in order to specify your own SDC Category |
| Include vertical seismic load effect | This checkbox is only active for SDC B. It can be used to set the vertical seismic load effect to zero if required. |
| Max earthquake spectral response acceleration | |
| Ss – short period (0.2s) | This figure can be determined from the maps found in ASCE 7-05 &-10 (units % of g, range 1 – 500) |
| S1 – 1.0s period | This figure can be determined from the maps found in ASCE 7-05 &-10 (units % of g, range 1 – 500) |
| Design spectral response spectral acceleration | |
| SDS – short period | This is automatically determined from SS and the site class, according to ASCE 7-05&-10 |
| SD1 – 1s period | This is automatically determined from S1 and the site class, according to ASCE 7-05&-10 |
| Next | Unless the SDC is type A, clicking Next takes you to the Structure Irregularities page described below; for SDC type A only, clicking Next takes you to the Seismic Loading page. |
Structure Irregularities page
For SDC types B to F this page is used to indicate any irregularities in plan or vertically.
| Property | Description |
|---|---|
| Structure Plan Irregularities | Check the appropriate boxes to define any plan irregularities. |
| Structure Vertical Irregularities | Check the appropriate boxes to define any vertical 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. |
| Use orthogonal seismic combinations | By default, the orthogonal seismic combination procedure is only activated when a Plan irreg 5 - Non parallel systems irregularity has been selected. However, by checking this box you can directly specify the use of orthogonal seismic combinations, (in which the seismic loadcases for both directions are included) when needed. |
| Next | Clicking Next takes you to the Fundamental Period page described below. |
Fundamental Period page
For SDC types B to F this page is used to determine the fundamental period, TDir 1 and TDir 2.
| Property | Description |
|---|---|
| Fundamental Period Definition | |
| Use approx fundamental period Ta | This is automatically derived from ASCE 7-05&-10 clause 12.8.2.1. |
| User defined fundamental period T | 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 | |
| Long period transition period, TL | This figure can be determined from figs 22-15, 16, 17, 18, 19 and 20 found in ASCE 7-05 or figs 22-12, 13, 14, 15 and 16 found in ASCE 7--10. |
| TS | This value is derived (Ts = SD1/SDS) |
| Fundamental Period Dir 1 and Dir 2 | |
| Structure Type | Select from Steel moment resisting frames, Concrete moment resisting frames, Eccentrically braced steel frames or All other structural systems (ref ASCE 7-05 / ASCE 7-10 Table 12.8-2 |
| Approx fundamental period, Ta | This is automatically derived from ASCE 7-05&-10 clause 12.8.2.1. |
| 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 Seismic Force Resisting System page described below. |
Seismic Force Resisting System page
For SDC types B to F this page is used to determine the response modification coefficient, R, and other factors in the X and Y directions.
| Property | Description |
|---|---|
| Seismic force resisting system Dir 1 and Dir 2 | |
| System | This field allows you to set the appropriate system, (eg. bearing wall, building frame, moment resisting frame etc.) from ASCE 7-05 &-10 Table 12.2-1. |
| Type | This field allows you to set the appropriate type for the chosen system from ASCE 7-05 &-10 Table 12.2-1. |
| Coefficients & Factors Dir 1 and Dir 2 | |
| Response modification coefficient, R | This is automatically derived, but you are given the facility to edit the calculated value. |
| System over-strength factor | This is automatically derived, but you are given the facility to edit the calculated value. |
| Deflection amplification factor, Cd | This is automatically derived, but you are given the facility to edit the calculated value. |
| Redundancy factor, ρ | This is automatically derived from the SDC, (SDC B-C ρ = 1.0, SDC D-F ρ = 1.3) but you are given the facility to edit the calculated value. |
| Next | Clicking Next takes you to the Effective Seismic Weight page described below. |
Effective Seismic Weight page
This page is used to determine the Structure Seismic Dead Weight.
You should include those loadcases that you want to contribute to the Structure Seismic Dead Weight.
Note:
The effective seismic weight combination is used to develop the seismic design loading and is not used in any 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 for using the ASCE 7 code outside of the US.
| 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. |
| Risk Category | 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. |
| Include localization - Check this box in order to display the below 'ELF & RSA' and 'RSA only' localization settings. | |
| 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, (ASCE 7 code value = 1/(R/I)). |
| User Defined Static Base Shear (Dir1 and Dir2) | This field allows you to override the code value for the static base shear, (ASCE 7 code value V = Cs x W and Cs = SDS / (R /Ie)). |
| % eccentricity for accidental torsion (Dir1 and Dir2) | This field allows you to override the code eccentricity for
accidental torsion, (ASCE 7 code 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),(ASCE 7 factor = 0.2 x SDS x Dead loads). |
| RSA only | (only available if RSA has been selected) |
| % Mass participation for RSA | This field allows you to set your own required % mass
participation, (ASCE 7 code 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, (ASCE 7 code value: 85% x V / Vt). |
| Scaling of Deflections for Drift Checks (% of Base Shear) (Dir1 and Dir2) | This field allows you to set your required scaling factors,
(ASCE 7 code value: 85% x V / Vt). Note: A zero factor means
no scaling will be performed on deflections. |
| Finish | Click Finish to automatically generate the Seismic loadcases and open the ASCE 7 Seismic Combination Generator described below. |
ASCE 7 Seismic Combination Generator
The Combination Generator sets up seismic combinations from the following ASCE 7 "core" combinations that include seismic loads.
ASD - Seismic Combinations
5) 1.0D + 0.714E
6) 1.0D + 0.75L + 0.536E + 0.75S
8) 0.6D + 0.714E
Note:
In ASCE, in the above 0.714 equates to 0.7 and 0.536 equates to 0.525. Tekla Structural Designer utilizes the ASCE factors - you can however change them if required.
LRFD - Seismic Combinations
5) 1.2D + 1.0E + 1.0L + 0.2S
7) 0.9D + 1.0E
(Where E is the seismic component of the loading in the combination.)
| 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 factors. |
| Finish | Click Finish to generate the Seismic combinations. |