Engineering structural design criteria
The 2019 Oregon Structural Specialty Code (OSSC)
Seismic
- Determine site specific seismic design parameters
- Site Class D is used unless the Building Official or a geotechnical report determines Site Class E or F soils are present.
Wind
- Wind exposure category must be determined by the Engineer of Record based onsite conditions
- The design wind speeds (3-second gust) are:
Risk category
I
II
III
IV
V (mph)
91
97
103
107
Vasd (mph)
70
75
80
83
Snow
- Per OSSC-19 Section 1608.1
Soils
- Foundation and retaining wall design parameters may be based on presumptive load-bearing values per 2019 OSSC-19 Table 1806.2, or as justified by submission of a Geotechnical Report.
- Default allowable foundation bearing capacity within the County is 1,500 pounds per square feet (psf).
- Default lateral soil loads should be 45 psf/ft for laterally unrestrained retaining walls and 60 psf/ft for laterally restrained retaining walls (basement walls). Lateral pressures for walls supporting sloping backfill or surcharge loads must be determined by a geotechnical report.
- Minimum frost depth is 12 inches for elevations less than 400 feet.
Residential prescriptive design (non-engineered) criteria
- Seismic: Design Category D
- Wind speed: 97 mph
- Roof snow load: 25 psf below 400 foot site elevation. All other elevations can be determined on Structural Engineers Association Organization (SEAO) website
- Frost depth: 12 inches
- Weather classification: Moderate