Cheatsheet: Load Analysis Dead, Live, Wind, Seismic

1. Dead Loads

1.1 Definition and Components

1.2 Unit Weights

2. Live Loads

2.1 Floor Live Loads

2.2 Live Load Reduction

2.3 Roof Live Loads

2.4 Snow Loads

2.4.1 Drift and Unbalanced Loads

• Leeward drift: p_d = h_dγ (h_d = drift height)
• Windward drift: p_d = (3/4)h_dγ
• Snow density γ: 0.13p_g + 14 (pcf), max 30 pcf
• Drift height based on windward fetch length and roof geometry
• Unbalanced loads apply to hip and gable roofs with slopes > 2.38° and <>

3. Wind Loads

3.1 Basic Parameters

3.2 Directional Procedure (Method 1)

3.2.1 Velocity Pressure Exposure Coefficient K_z

3.2.2 External Pressure Coefficients C_p

• Windward wall: +0.8
• Leeward wall: -0.5 (L/B ≤ 1) to -0.3 (L/B ≥ 4)
• Side walls: -0.7
• Roof (windward, slope ≤ 10°): -0.9 to -0.18
• Roof (leeward): -0.3 to -0.6
• Components and cladding have separate C_p values based on area and location

3.3 Envelope Procedure (Method 2 - Simplified)

3.4 MWFRS vs. Components and Cladding

4. Seismic Loads

4.1 Basic Parameters

4.2 Site Classification

4.3 Seismic Design Category

• Determined from Risk Category and S_DS, S_D1 values
• Categories: A (lowest) through F (highest seismicity)
• SDC A: S_DS <>
• SDC B: 0.167g ≤ S_DS <>
• SDC C: 0.33g ≤ S_DS <>
• SDC D: 0.50g ≤ S_DS or S_D1 ≥ 0.20g
• Higher SDC requires more stringent detailing and analysis

4.4 Equivalent Lateral Force Procedure

4.5 Fundamental Period T

4.6 Response Modification Factor R

4.7 Vertical Distribution of Forces

4.8 Horizontal Distribution and Torsion

4.9 Drift Limits

• Design story drift: Δ = C_dδ_xe/I_e
• δ_xe = deflection from elastic analysis
• C_d = deflection amplification factor (2.5 to 6 depending on system)

5. Load Combinations

5.1 LRFD Load Combinations (ASCE 7)

• 1.4D
• 1.2D + 1.6L + 0.5(L_r or S or R)
• 1.2D + 1.6(L_r or S or R) + (L or 0.5W)
• 1.2D + 1.0W + L + 0.5(L_r or S or R)
• 1.2D + 1.0E + L + 0.2S
• 0.9D + 1.0W
• 0.9D + 1.0E

5.2 ASD Load Combinations (ASCE 7)

• D
• D + L
• D + (L_r or S or R)
• D + 0.75L + 0.75(L_r or S or R)
• D + (0.6W or 0.7E)
• D + 0.75L + 0.75(0.6W) + 0.75(L_r or S or R)
• D + 0.75L + 0.75(0.7E) + 0.75S
• 0.6D + 0.6W
• 0.6D + 0.7E

5.3 Seismic Load Effect

5.4 Special Considerations

• Roof live load L_r: minimum 20 psf (12 psf for steep slopes)
• Rain load R accounts for ponding if roof drainage is inadequate
• For soil/hydrostatic loads H, use 1.6H in LRFD, 1.0H in ASD
• Fluid load F: 1.4F in LRFD, 1.0F in ASD
• Self-straining loads T (temperature): 1.2T in LRFD, 1.0T in ASD

6. Special Topics

6.1 Diaphragm Design Forces

6.2 Orthogonal Loading

• Apply 100% of forces in one direction plus 30% in perpendicular direction
• Required for structures with irregularities or SDC C and above
• Consider both positive and negative orthogonal combinations

6.3 Overturning and Uplift

6.4 P-Delta Effects

6.5 Nonbuilding Structures

• Tanks, vessels, bins: use specific R values (2.5-3.5)
• Electrical/mechanical equipment: use component seismic coefficients
• Chimneys and stacks: K_d = 0.95, special R values apply
• Sign structures: K_d = 0.85, R = 3.5

6.6 Impact Loads