Structural System - DUAL SYSTEM: Special Moment Frames (perimeter) + Buckling-Restrained Braced Frames (core).
Frame type - Continuous BRBF core; perimeter SMF resisting >= 25% of design seismic force at every level. Emergency Operations Center (EOC).
Number of stories - 9
Story heights - Level 1: 16 ft; Levels 2-9: 13 ft. Roof at 120 ft.
Analysis procedure - MRSA; SEISMIC DESIGN CATEGORY F. Near-fault site (S1 >= 0.75, Risk Category IV) - site-specific ground motion / near-fault considerations apply.
Design standards - AISC 360-22, AISC 341-22, AISC 358-22, ASCE 7-22.

## Material Properties
- SMF W-shapes, BRBF beams/columns: ASTM A992, Fy = 50 ksi
- BRB cores: ASTM A36 machined steel core (Fy per qualification); casing/mortar per manufacturer
- Connection / gusset / continuity plates: ASTM A572 Grade 50
- Floor system: composite - 3 1/4 in. NW concrete on 3 in. composite deck

## Gravity Loads
| Load Type | Magnitude |
|------------|-----------|
| Dead Load | 90 psf (composite floor + heavy MEP/redundant systems superimposed) |
| Cladding Load | 20 psf (blast/impact-rated envelope) |
| Floor Live Load | 100 psf (EOC operations/equipment); reducible per Sec. 4.7 limits |
| Roof Live Load | 20 psf (Lr) + 75 psf mechanical/antenna zone |

## Seismic Design Data
- S1 = 0.90 g (near-fault), SS = 2.00 g; SDS = 1.50 g, SD1 = 1.00 g, Site Class D
- RISK CATEGORY IV; Ie = 1.5
- SEISMIC DESIGN CATEGORY F (Risk Cat IV with S1 >= 0.75) <-- the defining condition
- Dual SMF + BRBF: R = 8, Cd = 5, Omega_0 = 2.5; SMF independently resists >= 25% of V at every level (Sec. 12.2.5.1)
- SDC F consequences the agent MUST apply: EXTREME irregularities (horizontal 1b, vertical 1b/5b) are PROHIBITED (Sec. 12.3.3.1); reduced/again-checked system height limits (Table 12.2-1 SDC F column); ELF not permitted (use MRSA); near-fault - a site-specific ground-motion (Ch 21) or the Chapter 11.4.8 requirements may be triggered (state the basis).
- Allowable story drift 0.010 h_sx (Risk Cat IV, Table 12.12-1). Redundancy rho = 1.3.

## Wind Design Data
- V = 130 mph (Risk Cat IV), Exposure C. Seismic clearly governs strength at SDS = 1.5 g; still report wind and confirm the 0.010 drift limit.

## Building Plan Geometry (REGULAR RECTANGLE - the challenge is SDC F, not shape)
- Overall: 140'-0" (X) x 100'-0" (Y), uniform all levels; keep it regular so no extreme irregularity is introduced.
- Column Grid: X = 5 bays @ 28'-0"; Y = 4 bays @ 25'-0".
- BRBF core: two braced bays each direction at the central core (Grids 3-4). Perimeter SMF: all four faces.

## Dual + SDC F Design Requirements
- Verify and DOCUMENT: no extreme torsional (1b) irregularity (compute the ratio; if it approaches 1.4, revise) - it is PROHIBITED in SDC F.
- Confirm each system's Table 12.2-1 height limit is satisfied in the SDC F column.
- SMF portion: SCWB, panel zone, RBS per A358, designed for >= 25% of V at every level (report the split).
- BRBF portion: adjusted brace strengths (beta*omega*Ry*Fy*Asc compression, omega*Ry*Fy*Asc tension) drive beams/columns/gussets; use omega, beta from the BRB qualification envelope.
- Apply Ie = 1.5 and the 0.010 h_sx drift limit throughout.

## Member Sizing Rules
- BRB core areas per story (change every 2 stories, never smaller below); one SMF beam per level per frame; SMF/BRBF columns change every 2 stories; splices 4 ft above floor.
- SMF and BRBF column bases fixed; gravity columns pinned.
