ASCE 7 horizontal design spectrum
ASCE 7 code spectra - Two Period
| Limits | Equation | Segment | Ref |
|---|---|---|---|
| 0 ≤ T ≤ T0 | SDS x (0.4 + 0.6 x T / T0 ) x (1/(R/Ie) | Start point/linear | 11.4.5 (1) |
| T0 ≤ T ≤ Ts | SDS x (0.4 + 0.6 x T / T0 ) x (1/(R/Ie) | Constant | 11.4.5 (2) |
| Ts ≤ T ≤ TL | (SD1/T)/(R/I) | Constant/T | 11.4.5 (3) |
| TL ≤ T ≤ 4s | (SD1 x TL / T2)/(R/I) | Constant/T2 | 11.4.5 (4) |
ASCE 7 site specific spectra (user defined - based on SD and T)
Note: ASCE 7 has either sloped second segment
or horizontal 4th segment - not both.
Parameters
- SDuser(0) – units g
- SDuser(T0user) – units g
- T0user – units sec
- TSuser – units sec
- TLuser – units sec
- T4user – units sec, default = 4s
Input limits
- SDuser(0) > 0
- SDuser(T0user) > 0 if T0user > 0
- 0s ≤ T0user < TSuser < TLuser ≤ T4user
Curve Equations
Design Response Spectrum curves for Sa(g) are defined by
Note: same curve for both Dir1 and Dir2
| Line | Limits | Equation |
|---|---|---|
| (1) – straight line | 0 ≤ T ≤ T0user | Sa(g)(T) = SDuser(0) + ((SDuser(T0user) – SDuser(0)) x T / T0user) |
| (2) – straight line | T0user ≤ T ≤ TSuser | Sa(g)(T) = SDuser(T0user) |
| (3) – curve | TSuser ≤ T ≤ TLuser | Sa(g)(T) = SDuser(T0user) x TSuser/ T |
| (4) – curve | TLuser ≤ T ≤ T4user | Sa(g)(T) = SDuser (T0user) x TSuser x TLuser/ T2 |
| (5) – straight line continued from (4) |
Adjusted Design Response Spectrum curves for Sa(g)/(R/Ie) are defined by
Note: same curve for both Dir1 and Dir2
| Line | Limits | Equation |
|---|---|---|
| (1) – straight line | 0 ≤ T ≤ T0user | SD(T) = [SDuser(0) + ((SDuser(T0user) - SDuser(0)) x T / T0user)] /(R/Ie) |
| (2) – straight line | T0user ≤ T ≤ TSuser | SD(T) = SDuser(T0user) / (R/Ie) |
| (3) – curve | TSuser ≤ T ≤ TLuser | SD(T) = SDuser(T0user) x TSuser / T / (R/Ie) |
| (4) – curve | TLuser ≤ T ≤ T4user | SD(T) = SDuser(T0user) x TSuser x TLuser / T2 / (R/Ie) |
| (5) – straight line continued from (4) |
Note:
If T0user = 0, then no line (1) exists
If TLuser = T4user then no line (4) exists
ASCE 7/UBC site specific spectra - user defined (Taiwan)
Horizontal design spectrum
Taiwan code Figure 2
Specifically, the last section of curve (Segment 4) extends horizontally from 2.5T0 with a value of 0.4 x SDS
Note: The above
curve can be obtained by selecting Horizontal 4th Segment on the Site Specific
Spectra page of the Seismic Wizard.
ASCE 7/UBC site specific spectra - user defined (Thailand)
Horizontal design spectrum
When Sd1 > Sds
Thailand code Figure 1-4-3
Specifically, the previously flat section of curve (Segment 2) rises from SDS at T = 0.2 to SD1 At T = 1.0
Note: The above curve
can be obtained by selecting Sloped 2nd Segment on the Site Specific Spectra page of
the Seismic Wizard.
ASCE 7 site specific spectra (user defined - generic curve)
A site specific generic curve can be defined, either manually, or by pasting data from a spreadsheet. This procedure requires an RSA to be run (not ELF). This has been added primarily for remote markets using ASCE 7
For further details, see the following video: User defined RSA curve