Input Data
Example Data Table
| Case | Risk Category | SMS | SM1 | SDS | SD1 | Near Fault | Screening SDC |
|---|---|---|---|---|---|---|---|
| Warehouse | II | 0.45 | 0.12 | 0.30 | 0.08 | No | B |
| Office Tower | III | 0.90 | 0.33 | 0.60 | 0.22 | No | D |
| Hospital | IV | 1.35 | 1.20 | 0.90 | 0.80 | No | E |
| Fault Adjacent Facility | II | 1.05 | 0.42 | 0.70 | 0.28 | Yes | F |
Formula Used
1. Derive design spectral accelerations when needed.
SDS = (2 / 3) × SMS
SD1 = (2 / 3) × SM1
2. Determine category from SDS thresholds.
For many projects, higher SDS values move the design category upward from A toward D.
3. Determine category from SD1 thresholds.
Long-period demand can increase the category, especially when SD1 reaches high levels.
4. Select the governing category.
Governing SDC = max(SDC from SDS, SDC from SD1)
5. Apply near-fault screening.
If a near-fault trigger governs, the screening category becomes F.
This calculator provides a practical screening workflow. Final classification should always be checked against the governing code edition, mapped hazard values, site class rules, and project jurisdiction.
How to Use This Calculator
- Select the project risk category.
- Enter SDS and SD1 directly, or enter SMS and SM1.
- Choose whether a near-fault trigger applies.
- Click the calculate button.
- Review the result block above the form.
- Export the output as CSV or PDF.
- Confirm the result with the applicable structural code.
Frequently Asked Questions
1. What does seismic design category represent?
It groups a structure by expected seismic demand and importance. Designers use it to select analysis methods, detailing rules, and system limitations.
2. Can I enter SMS and SM1 instead of SDS and SD1?
Yes. The calculator derives design values using two-thirds multipliers. Direct SDS and SD1 inputs override the derived values when both sets are entered.
3. Why are two categories shown?
One category comes from short-period demand using SDS. The other comes from one-second demand using SD1. The higher category governs the screening result.
4. When does category E appear?
Category E appears when long-period demand is very high. In this calculator, that occurs when SD1 reaches 0.75 or greater, unless category F governs.
5. What does the near-fault option do?
It forces a screening result of category F. Use it only when project conditions and code provisions indicate a near-fault or special seismic trigger.
6. Is the importance factor changing the category here?
The importance factor is stored for reporting and review. This screening workflow bases category selection on spectral values, risk category, and the near-fault choice.
7. Is this enough for final permit design?
No. It is a fast screening tool. Final engineering decisions should include site class, mapped values, local amendments, structural system checks, and code-specific exceptions.