The Ontario Building Code | Site Properties
4.1.8.4. Site Properties
(1) The peak ground acceleration (PGA) and the 5% damped spectral response acceleration values, Sa(T), for the reference ground conditions (Site Class C in Table 4.1.8.4.A.) for periods T of 0.2 s, 0.5 s, 1.0 s, and 2.0 s, shall be determined in accordance with Subsection 1.1.2. and are based on a 2% probability of exceedance in 50 years.
(2) Site classifications for ground shall conform to Table 4.1.8.4.A. and shall be determined using 
S except as provided in Sentence (3).
(3) If average shear wave velocity, S, is not known, Site Class shall be determined from energy-corrected Average Standard Penetration Resistance, 
60, or from soil average undrained shear strength, su, as noted in Table 4.1.8.4.A., 60and su being calculated based on rational analysis.
(4) Acceleration- and velocity-based site coefficients, Fa and Fv, shall conform to Tables 4.1.8.4.B. and 4.1.8.4.C. using linear interpolation for intermediate values of Sa(0.2) and Sa(1.0).
(5) Site-specific evaluation is required to determine Fa and Fv for Site Class F.
(6) For structures with a fundamental period of vibration equal to or less than 0.5 s that are built on liquefiable soils, Site Class and the corresponding values of Fa and Fv may be determined as described in Tables 4.1.8.4.A., 4.1.8.4.B., and 4.1.8.4.C. by assuming that thesoils are not liquefiable.
(7) The design spectral acceleration values of S(T) shall be determined as follows, using linear interpolation for intermediate values of T:
S(T) = FaSa(0.2) for T≤0.2 s
= FvSa(0.5) or FaSa(0.2), whichever is smaller for T = 0.5 s
= FvSa(1.0) for T = 1.0 s
= FvSa(2.0) for T = 2.0 s
= FvSa(2.0)/2 for T ≥4.0 s
Table 4.1.8.4.A.
Site Classification for Seismic Site Response
Forming Part of Sentences 4.1.8.4.(1) to (3)
| Item | Column 1 | Column 2 | Column 3 | Column 4 | Column 5 |
|
| Site Class | Ground Profile Name | Average Properties in Top 30 m |
| |
|
|
|
| Average Shear Wave Velocity, | Average Standard Penetration Resistance, | soil Undrained Shear Strength, su |
| 1. | A | Hard rock(1) (2) |
| N/A | N/A |
| 2. | B | Rock(1) | 760< | N/A | N/A |
| 3. | C | Very dense soil and soft rock | 360< |
| su > 100kPa |
| 4. | D | Stiff soil | 180< | 15 ≤ | 50 kPa < su ≤100 kPa |
| 5. | E | Soft soil |
|
| su < 50 kPa |
|
|
|
| Any profile with more than 3 m of soil with the following characteristics: | ||
|
|
|
| • plasticity index: PI>20 |
| |
|
|
|
| • moisture content w ≥40%, and |
| |
|
|
|
| • undrained shear strength: su < 25 kPa |
| |
| 6. | F | Other soils(3) | Site-specific evaluation required |
| |
Notes to Table 4.1.8.4.A.:
(1) Site Classes A and B, hard rock and rock, are not to be used if there is more than 3 m of softer materials between the rock and the underside of footing or mat foundations. The appropriate Site Class for such cases is determined on the basis of the average properties of the total thickness of the softer materials.
(2) If
S has been measured in-situ, the Fa and Fv values derived from Tables 4.1.8.4.B. and 4.1.8.4.C. may be multiplied by (1500/S)1/2.
(3) Othersoils include:
(a) liquefiable soils, quick and highly sensitive clays, collapsible weakly cemented soils, and other soils susceptible to failure or collapse under seismic loading,
(b) peat and/or highly organic clays greater than 3 m in thickness,
(c) highly plastic clays (PI > 75) more than 8 m thick, and
(d) soft to medium stiff clays more than 30 m thick.
Table 4.1.8.4.B.
Values of Fa as a Function of Site Class and Sa(0.2)
Forming Part of Sentence 4.1.8.4.(4)
| Item | Column 1 | Column 2 | Column 3 | Column 4 | Column 5 | Column 6 |
|
| Site Class | Values of Fa |
|
|
|
|
|
|
| Sa(0.2)≤0.25 | Sa(0.2)=0.5 | Sa(0.2)=0.75 | Sa(0.2)=1.00 | Sa(0.2)≥1.25 |
| 1. | A | 0.7 | 0.7 | 0.8 | 0.8 | 0.8 |
| 2. | B | 0.8 | 0.8 | 0.9 | 1.0 | 1.0 |
| 3. | C | 1.0 | 1.0 | 1.0 | 1.0 | 1.0 |
| 4. | D | 1.3 | 1.2 | 1.1 | 1.1 | 1.0 |
| 5. | E | 2.1 | 1.4 | 1.1 | 0.9 | 0.9 |
| 6. | F | (1) | (1) | (1) | (1) | (1) |
Notes to Table 4.1.8.4.B.:
(1) See Sentence 4.1.8.4.(5)
Table 4.1.8.4.C.
Values of Fv as a Function of Site Class and Sa(1.0)
Forming Part of Sentence 4.1.8.4.(4)
| Item | Column 1 | Column 2 | Column 3 | Column 4 | Column 5 | Column 6 |
|
| Site Class | Values of Fv |
|
|
|
|
|
|
| Sa(1.0)≤0.1 | Sa(1.0)=0.2 | Sa(1.0)=0.3 | Sa(1.0)=0.4 | Sa(1.0)≥0.5 |
| 1. | A | 0.5 | 0.5 | 0.5 | 0.6 | 0.6 |
| 2. | B | 0.6 | 0.7 | 0.7 | 0.8 | 0.8 |
| 3. | C | 1.0 | 1.0 | 1.0 | 1.0 | 1.0 |
| 4. | D | 1.4 | 1.3 | 1.2 | 1.1 | 1.1 |
| 5. | E | 2.1 | 2.0 | 1.9 | 1.7 | 1.7 |
| 6. | F | (1) | (1) | (1) | (1) | (1) |
Notes to Table 4.1.8.4.C.:
(1) See Sentence 4.1.8.4.(5)