Structural Loading — Design Architect Knowledge Base

Load Types

Dead Loads (D) — Self-Weight

Assembly	PSF
Residential floor (wood frame + subfloor + finish)	10–15
Precast hollow-core plank (8")	55–65
Precast + recovered oak overlay (3/4")	58–68
Exterior wood stud wall (2×6 + sheathing + siding)	8–12
Interior partition (2×4 + GWB both sides)	6–8
Asphalt shingle roof (shingles + sheathing + trusses)	10–12
Steel beam W12×26	26 plf
Steel column W10×26	26 plf
Fiber cement panel facade	3–5
Continuous rigid insulation (1" polyiso)	0.2

Live Loads (L) — IRC/IBC Required

Use	PSF	Code Reference
Residential floor (living areas)	40	IRC R301.5
Sleeping rooms	30	IRC R301.5
Uninhabitable attic (no storage)	10	IRC R301.5
Uninhabitable attic (limited storage)	20	IRC R301.5
Habitable attic with fixed stairs	30	IRC R301.5
Decks and balconies	40	IRC R301.5
Guardrails (concentrated)	200 lbs	IRC R301.5
Roof live load (maintenance)	20	IBC 1607.12
Roof live load (slope > 4:12)	15	IBC 1607.12

Snow Loads (S) — Rhode Island

Location	Ground Snow (pg) PSF
Coastal RI (Newport, Narragansett)	25–35
Central RI (Cranston, Warwick)	30–40
Northern RI (Woonsocket, Burrillville)	35–40
Reference	IBC Table 1608.1, ASCE 7-22 Ch 7

Roof snow load: pf = 0.7 × Ce × Ct × Is × pg

Ce = exposure factor (0.8 windswept, 1.0 normal, 1.2 sheltered)
Ct = thermal factor (1.0 heated, 1.1 unheated)
Is = importance factor (1.0 residential)

Wind Loads — Rhode Island

Parameter	Value
Basic wind speed (Risk Category II)	115–130 mph
Coastal exposed areas	Up to 130–140 mph
Exposure category (typical residential)	B or C
Reference	ASCE 7-16 Table 1609.3

Main wind force resisting system (MWFRS): Directional procedure per ASCE 7 Ch 27-28. For residential ≤ 60' mean roof height, simplified procedure (Ch 28) typically applies.

Seismic Loads — Rhode Island

Parameter	Value
Seismic Design Category	A (minimal)
Ss (short period)	≤ 0.15g
S1 (1-second period)	≤ 0.04g
Consequence	Exempt from detailed seismic analysis
Prescriptive connections	Acceptable

Load Combinations

LRFD (Strength Design)

1.4D

1.2D + 1.6L + 0.5(Lr or S or R) ← critical gravity combo

1.2D + 1.6(Lr or S or R) + (L or 0.5W)

1.2D + 1.0W + L + 0.5(Lr or S or R)

1.2D + 1.0E + L + 0.2S

0.9D + 1.0W ← critical uplift combo

0.9D + 1.0E

ASD (Allowable Stress Design)

D + L

D + (Lr or S or R)

D + 0.75L + 0.75(Lr or S or R)

D + 0.6W (or 0.7E)

Load Path — Gravity

Roof shingles → Sheathing → Trusses (top chord)
    ↓
Truss reactions → Top plate (bearing wall or steel beam)
    ↓
Steel beam → Bolted end-plate connection → Steel column
    ↓
Column base plate → Anchor bolts → Grade beam / Spread footing
    ↓
Soil (bearing capacity 2,000–2,500 PSF typical RI)

Load Path — Lateral (Wind)

Wind pressure on facade panels
    ↓
Panel clips → Steel column flanges (bolted DfD)
    ↓
Column moment connection → Steel beam (moment frame action)
    ↓
Base plate → Anchor bolts → Foundation (overturning resistance)
    ↓
Soil passive pressure + footing weight (sliding resistance)

Tributary Area Calculations

For a steel beam supporting joists from both sides:

Tributary width = (span_north / 2) + (span_south / 2)
Linear load (plf) = (D + L) psf × tributary width (ft)

For a column (interior):

Tributary area = bay_width × bay_depth
Column axial load = (D + L) psf × tributary area (sf) × number of floors

Example — ML Systems 20' × 20' bay, 2-story:

D = 15 psf (floor) + 12 psf (roof) = 27 psf per floor
L = 40 psf (floor) + 30 psf (roof snow)
Tributary area = 20' × 20' = 400 sf

Interior column load (LRFD):
  Floor: 1.2(15×400) + 1.6(40×400) = 7,200 + 25,600 = 32,800 lbs
  Roof:  1.2(12×400) + 0.5(30×400) = 5,760 + 6,000 = 11,760 lbs
  Total: 44,560 lbs ≈ 44.6 kips

Corner column (1/4 tributary): ≈ 11.1 kips
Edge column (1/2 tributary): ≈ 22.3 kips

Deflection Limits

Condition	Limit	20' Span Max Deflection
Floor live load (GWB ceiling)	L/360	0.67"
Floor total load	L/240	1.00"
Roof live load	L/360	0.67"
Roof total load	L/180	1.33"
Tile/stone flooring	L/720	0.33"
Precast hollow-core (typical)	L/360	0.67"

Formula: δ = 5wL⁴ / (384EI) for uniform load

w = load per unit length
L = span
E = modulus of elasticity
I = moment of inertia

Steel Properties — ML Steel vs A36

Property	A36	HSLA 60 ksi	HSLA 80 ksi
Yield strength (Fy)	36 ksi	60 ksi	80 ksi
Tensile strength (Fu)	58 ksi	75 ksi	90 ksi
Modulus of elasticity (E)	29,000 ksi	29,000 ksi	29,000 ksi
Strength ratio vs A36	1.0×	1.67×	2.22×
Cost premium vs A36	—	~15%	~24%
Weight savings (same capacity)	—	25–35%	35–50%
Source	Mill	ML recycled auto	ML recycled auto

Key insight: E is identical across all steel grades — deflection depends on geometry (I), not strength (Fy). Higher-strength steel allows lighter SECTIONS but the moment of inertia may be lower, so deflection must be checked independently of strength.

Foundation Design

Soil Bearing — Rhode Island

Soil Type	Allowable Bearing (PSF)
Bedrock	12,000+
Dense gravel/sand (compacted)	3,000–4,000
Medium sand, glacial till	2,000–3,000
Stiff clay	2,000
Soft clay/silt	1,000–1,500
RI typical (prescriptive)	2,000

Frost Depth

Location	Frost Depth
Most of RI	40"
Block Island (New Shoreham)	30"
Practical design	42"–48" (safety margin)

Spread Footing Sizing

Required area = Column load (service) / Allowable soil bearing
Example: 45 kips / 2,000 psf = 22.5 sf → 4'-9" × 4'-9" pad

Multi-Cycle Over-Engineering

Size footings for N+2 future stories above current design
Embed stub plates in grade beams (A36 plate, A325 anchor bolts)
Upfront cost premium: 5–10%
Avoids future underpinning: saves 20–30% on expansion
Column base plates designed for future axial load + moment

Structural Loading & Analysis