501.3.4 Expected Loads
- Dead loads.
- Live loads.
- Impact loads.
- Explosion loads.
- Soil and hydrostatic pressure loads.
- Flood loads (mean return period).
Small: 100 years
Medium: 500 years
Large: Determined on a site-specific basis
Very Large: Determined on a site-specific basis
- Wind loads (mean return period).
Small: 50 years
Medium: 75 years
Large: 100 years
Very Large: 125 years
- Wind-borne debris loads.
- Snow loads (mean return period).
Small: 25 years
Medium: 30 years
Large: 50 years
Very Large: 100 years
- Rain loads. See Table 501.3.4.
- Earthquake loads (mean return period).
Small: 25 years
Medium: 72 years
Large: 475 years, but need not exceed two-thirds of the intensity of very large loads
Very Large: 2,475 years. At sites where the 2,475-year, 5-percent damped spectral response acceleration at a 0.3-second period exceeds 1.5 g and at a 1-second period exceeds 0.6 g, very large ground shaking demands need not exceed a 5-percent damped response spectrum that at each period is 150 percent of the median spectral response acceleration ordinate resulting from a characteristic earthquake on any known active fault in the region.
- Ice loads, atmospheric icing (mean return period).
Small: 25 years
Medium: 50 years
Large: 100 years
Very Large: 200 years
- Hail loads.
- Thermal loads.
| MAGNITUDE OF EVENT | DRAINAGE SYSTEM | MRI (YEARS) | STORM DURATION (MIN.) |
| Small | Primary | 25 | 60 |
| Small | Secondary | 25 | 15 |
| Medium | Primary | 50 | 60 |
| Medium | Secondary | 50 | 15 |
| Large | Primary | 100 | 60 |
| Large | Secondary | 100 | 15 |
| Very Large | Primary | 100 | 30 |
| Very Large | Secondary | 100 | 10 |