IS893 (Part 1) Horizontal Design Spectrum
IS893 (Part 1) code spectra
For rocky, or hard soil sites
| Limits | Damping factor | Segment |
|---|---|---|
| 0 ≤ T ≤ 0.10 | (1 + 15 T) | Start point/linear |
| 0.10 ≤ T ≤ 0.40 | (2.50) | Constant/T |
| 0.40 ≤ T ≤ 4.00 | (1.00/T) | Constant/T2 |
For medium soil sites
| Limits | Damping factor | Segment |
|---|---|---|
| 0 ≤ T ≤ 0.10 | (1 + 15 T) | Start point/linear |
| 0.10 ≤ T ≤ 0.55 | (2.50) | Constant/T |
| 0.55 ≤ T ≤ 4.00 | (1.36/T) | Constant/T2 |
For soft soil sites
| Limits | Damping factor | Segment |
|---|---|---|
| 0 ≤ T ≤ 0.10 | (1 + 15 T) | Start point/linear |
| 0.10 ≤ T ≤ 0.67 | (2.50) | Constant/T |
| 0.67 ≤ T ≤ 4.00 | (1.67/T) | Constant/T2 |
IS893 (Part 1) site specific spectra - user defined
Note: In this example T3user = T4user so there
is no line (4)
Parameters
- Damping factoruser
- Sauser/g(0) – units g
- Sauser/g(T1user) – units g
- T1user – units sec
- T2user – units sec
- T3user – units sec, default = 4s
- T4user – units sec, default = 4s
Input limits
- Sauser/g(0) > 0
- Sauser/g(T1user) > 0
- 0s ≤ T1user < T2user < T3user ≤ T4user
Curve Equations
Average 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 ≤ T1user | Sa(g)(T) = Damping factoruser x [Sauser/g(0) + ((Sauser/g(T1user) – Sauser/g(0)) x T / T1user)] |
| (2) – straight line | T1user ≤ T ≤ T2user | Sa(g)(T) = Damping factoruser x Sauser/g (T1user) |
| (3) – curve | T2user ≤ T ≤ T3user | Sa(g)(T) = Damping factoruser x Sauser/g (T1user) x T2user/ T |
| (4) – curve | T3user ≤ T ≤ T4user | Sa(g)(T) = Damping factoruser x Sauser/g (T1user) x T2user x T3user/ T2 |
| (5) – straight line continued from (4) |
Design Response Spectrum curves for Ah(g) (=Sa/g/((2xR)/(ZxI))) are defined by
Note: same curve for both Dir1 and Dir2
| Line | Limits | Equation |
|---|---|---|
| (1) – straight line | 0 ≤ T ≤ T1user | Ah(g)(T) = Damping factoruser x
[Sauser/g(0) + ((Sauser/g(T0) –
Sauser/g(0)) x T / T1user)] But not less than Z/2 |
| (2) – straight line | T1user ≤ T ≤ T2user | Ah(g)(T) = Damping factoruser x Sauser/g (T1user) / ((2xR)/(ZxI)) |
| (3) – curve | T2user ≤ T ≤ T3user | Ah(g)(T) = Damping factoruser x Sauser/g (T1user) x T2user/ T / ((2xR)/(ZxI)) |
| (4) – curve | T3user ≤ T ≤ T4user | Ah(g)(T) = Damping factoruser x Sauser/g (T1user) x T2user x T3user/ T2 / ((2xR)/(ZxI)) |
| (5) – straight line continued from (4) |
Note:
If T1user = 0, then no line (1) exists
If T3user = T4user then no line (4) exists