StructSuite seismic loads — ELF wizard (ASCE 7-22)
Reference: ASCE/SEI 7-22 Chapter 12 (ELF, Section 12.8), Chapter 11 (definitions, Section 11.4 spectral values).
Technical version: 1.0 (May 2026) — aligned with SeismicWizardApp accordion titles and content/wizard-labels/seismic.json (Step labels match the UI; example copy may use the same section keys).
Companion (wind MWFRS): ASCE 7-22 Wind Loads on MWFRS (StructSuite Wind Module).
1. Scope
The module implements the equivalent lateral force (ELF) procedure for horizontal seismic forces: Cs, base shear V, vertical distribution Fx, story shears Vx, and diaphragm design forces Fpx per Section 12.8. It does not replace project-specific irregularity checks, redundancy ρ, drift, or detailing outside the wizard inputs.
2. Wizard steps (on-screen order)
| Step | Title in app | Role |
|---|---|---|
| 1 | Step 1: Building geometry and weights | Story table: wx (lb) per level; height mode hsx (story height) or hx (height from base)—hx is derived from hsx or edited to back-calculate story heights. hn = structural height from stories (Section 11.2). Total W = Σwx. |
| 2 | Step 2: Site Classification and Spectral Parameters | Table 20.2-1 site class; Ss, S1, SMS, SM1, TL (manual or workflow aligned with ASCE Hazard Tool guidance in UI). Displays SDS, SD1, and SDC when inputs support them. |
| 3 | Step 3: Risk Category and Importance Factor | Table 1.5-1 risk category and Ie (Section 11.5). |
| 4 | Step 4: Seismic Force-Resisting System | Table 12.2-1 system selection (R, Cd, Ω0). Options in UI for Section 12.8.1.3 max SDS simplification (when criteria are met), structural irregularity attestation, and ρ = 1.0 when permitted. |
| 5 | Step 5: Period Determination | Ta from Ct hnx (approximate), or moment-frame / shear-wall formulas, or user T (direct). |
| 6 | Step 6: Seismic Response Coefficient Cs | Cs per Section 12.8.1 with expanded calculation detail (including caps and T ≤ TL / T > TL branches as implemented). |
| 7 | Step 7: Vertical and Horizontal Distribution | Base shear V, Fx, Vx; expanded rows reference Section 2.3.6 (strength design) and Section 2.3.5 (0.7E for allowable stress design) where shown. |
| 8 | Step 8: Diaphragm Design Forces | Fpx per Section 12.10.1 (and related limits as coded). |
Red / blue summary lines under each step follow the same completion pattern as the wind module: required inputs stay red until satisfied, then blue summaries show key results.
3. Implementation notes (read before peer review)
- Story order: Levels are managed in building order (lowest level = 1); the table display may list upper stories first while hx accumulates from the base—confirm hn and Fx against your hand check if your office uses a different numbering convention.
- hsx vs hx: Toggle matches Section 11.2 definitions in the in-app note (hn, hx, hsx, wx).
- Site class and SDS: UI copy references Section 12.8.1.3 and that Site Class E or F affects whether the max SDS shortcut may be used.
- Decimals: Spectral and coefficient displays use fixed decimal formatting in the app; round only at the reporting stage you use for the calc package.
4. Related design examples
Seismic design examples in content/examples/seismic/ use content/module-steps/seismic.json and content/wizard-labels/seismic.json for “In StructSuite:” step text.