Structural System - Special Concentrically Braced Frame (SCBF)
Frame type - ALL braced bays concentrated in an OFFSET core at the east end (torsionally irregular by design); notched rectangular plan; partial rooftop amenity level
Number of stories - 9 + partial Level 10 (rooftop amenity/mechanical over east third)
Story heights - Level 1: 15 ft; Levels 2-9: 12 ft 6 in; Level 10 (partial): 12 ft. Main roof 115 ft; amenity roof 127 ft.
Analysis procedure - MRSA with amplified accidental torsion; SDC D
Design standards - AISC 360, AISC 341 (Section F2), ASCE 7

## Material Properties
- W-shapes: **ASTM A992**, **Fy = 50 ksi**
- Braces (round HSS): **ASTM A500 Grade C**, **Fy = 46 ksi**
- Gusset plates: **ASTM A572 Grade 50**
- Floor system: composite - 3 1/4 in. LW concrete on 3 in. deck

## Gravity Loads
| Load Type | Magnitude |
|------------|-----------|
| Dead Load | 80 psf typical; 105 psf Level 10 amenity floor (topping + planters) |
| Cladding Load | 18 psf |
| Floor Live Load | 50 psf office + 15 psf partitions; 100 psf Level 10 amenity (assembly); reducible per Sec. 4.7 |
| Roof Live Load | 20 psf (Lr) at both roof levels |
| Mechanical | 60 psf allowance over Grids 7-8 / B-C at Level 10 |

## Seismic Design Data
- SDS = 1.00 g, SD1 = 0.55 g, Site Class D, Risk Category II, Ie = 1.0, SDC D
- SCBF: R = 6, Cd = 5, Omega_0 = 2
- Height 115 ft (<160 ft SDC D limit) - OK; partial Level 10 treated as a story for the east zone
- EXPECTED horizontal irregularity Type 1a or 1b (torsional): core offset east. Agent must compute drift ratios at plan extremes, classify, amplify accidental torsion (Ax up to 3.0), and check whether Type 1b invokes additional SDC D prohibitions/penalties (rho = 1.3 likely).

## Wind Design Data
- V = 110 mph, Exposure B. Torsional wind load cases (ASCE 7 Fig. 27.3-8) meaningful here.

## Building Plan Geometry (NOTCHED RECTANGLE, OFFSET CORE)
  - Column Grid:
      - X-Axis: Grids 1 to 8 (7 bays @ 29'-0" = 203'-0")
      - Y-Axis: Grids A to D (3 bays @ 29'-0" = 87'-0")
  - NOTCH (all levels): zone Grids 1-2 / C-D (29' x 29') is OPEN (no framing) - northwest corner cut-out
  - Levels 1-9: full notched plan
  - LEVEL 10 (partial): Grids 6-8 / A-D only (58' x 87'); remainder of Level 9 roof is unoccupied membrane roof
  - Elevations: main roof 115'-0"; Level 10 amenity roof 127'-0"

## SCBF Bay Locations (ALL in the east core zone; two-story X configuration; bays 29'-0" wide)
Transverse (Y) Direction:
  - Frame Y1: Grid 7, between A-B, Levels 1-10
  - Frame Y2: Grid 7, between C-D, Levels 1-10
  - Frame Y3: Grid 8, between B-C, Levels 1-10
Longitudinal (X) Direction:
  - Frame X1: Grid B, between 6-7, Levels 1-10
  - Frame X2: Grid C, between 6-7, Levels 1-10
  - Frame X3: Grid B, between 7-8, Levels 1-9
  - NOTE: NO braced bays west of Grid 6. The west 145 ft of the building is gravity-only and is dragged to the core by collectors.

## SCBF Requirements (AISC 341 F2)
- Two-story X; braces meet at module mid-height columns/beams
- Highly ductile b/t and slenderness; KL/r <= 200
- Capacity design: columns/beams for expected brace strengths (tension Ry Fy Ag; compression 1.14 Fcre Ag; post-buckling 0.3 x compression) in the governing plastic mechanism combinations
- Gussets: 2t fold-line clearance, UFM
- Exempt no member from moderately/highly ductile checks in the core

## Member Sizing Rules
- One brace size, one beam size, one column size per 2-story module per frame
- Columns change every 2 stories; splices 4 ft above floor; never smaller below
- Gravity framing: one beam + one column size per story (agent to determine); infill @ 9'-8" o.c.
- Base fixity: all pinned. Gravity connections pinned.
