The Ontario Building Code | SFRS Force Reduction Factors, System Overstrength Factors, and General Restrictions
4.1.8.9. SFRS Force Reduction Factors, System Overstrength Factors, and General Restrictions
(1) The values of Rd and Ro and the corresponding system restrictions shall conform to Table 4.1.8.9. and the requirements of this Subsection.
(2) When a particular va1ue of Rd is required by this Article, the corresponding Ro shall be used.
(3) For combinations of different types of SFRS acting in the same direction in the same storey, RdRo shall be taken as the lowest value of RdRo corresponding to these systems.
(4) For vertical variations of RdRo, excluding rooftop structures not exceeding two storeys in height whose weight is less than the greater of 10% of W and 30% of Wi of the level below, the value of RdRo used in the design of any storey shall be less than or equal to the lowest value of RdRo used in the given direction for the storeys above, and the requirements of Sentence 4.1.8.15.(5) must be satisfied.
(5) If it can be demonstrated through testing, research and analysis that the seismic performance of a structural system is at least equivalent to one of the types of SFRS mentioned in Table 4.1.8.9., then such a structural system will qualify for values of Rd and Ro corresponding to the equivalent type in that Table.
Table 4.1.8.9.
SFRS Ductility-Related Force Modification Factors, Rd, Overstrength-Related Force Modification Factors, Ro, and General Restrictions (1)
Forming Part of Sentence 4.1.8 9.(1)
| Item | Column 1 | Column 2 | Column 3 | Column 4 | Column 5 | Column 6 | Column 7 | Column 8 |
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| Type of SFRS |
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| Restrictions(2) |
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| |
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| Rd | Ro | Cases Where IEFaSa(0.2) | Cases Where IEFvSa(1.0) | |||
|
|
|
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| <0.2 | ≥0.2 to <0.35 | ≥0.35 to ≤0.75 | >0.75 | >0.3 |
| 1. | Steel Structures designed and Detailed According to CSA S16(3) |
|
|
|
|
| ||
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| Ductile moment-resisting frames | 5.0 | 1.5 | NL | NL | NL | NL | NL |
|
| Moderately ductile moment-resisting frames | 3.5 | 1.5 | NL | NL | NL | NL | NL |
|
| Limited ductility moment-resisting frames | 2.0 | 1.3 | NL | NL | 60 | 30 | 30 |
|
| Moderately ductile concentrically braced frames |
|
|
|
|
|
|
|
|
| Tension-compression braces | 3.0 | 1.3 | NL | NL | 40 | 40 | 40 |
|
| Tension only braces | 3.0 | 1.3 | NL | NL | 20 | 20 | 20 |
|
| Limited ductility concentrically braced frames |
|
|
|
|
|
|
|
|
| Tension-compression braces | 2.0 | 1.3 | NL | NL | 60 | 60 | 60 |
|
| Tension only braces | 2.0 | 1.3 | NL | NL | 40 | 40 | 40 |
|
| Ductile buckling-restrained braced frames | 4.0 | 1.2 | NL | NL | 40 | 40 | 40 |
|
| Ductile eccentrically braced frames | 4.0 | 1.5 | NL | NL | NL | NL | NL |
|
| 5.0 | 1.6 | NL | NL | NL | NL | NL | |
|
| Limited ductility plate walls | 2.0 | 1.5 | NL | NL | 60 | 60 | 60 |
|
| Conventional construction of moment-resisting frames, braced frames or plate walls |
|
|
|
|
|
|
|
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| Assembly occupancies | 1.5 | 1.3 | NL | NL | 15 | 15 | 15 |
|
| Other occupancies | 1.5 | 1.3 | NL | NL | 60 | 40 | 40 |
|
| Other steel SFRS(s) not defined above | 1.0 | 1.0 | 15 | 15 | NP | NP | NP |
| 2. | Concrete Structures designed and Detailed According to CAN/CSA-A23.3 |
|
|
|
| |||
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| Ductile moment-resisting frames | 4.0 | 1.7 | NL | NL | NL | NL | NL |
|
| Moderately ductile moment-resisting frames | 2.5 | 1.4 | NL | NL | 60 | 40 | 40 |
|
| 4.0 | 1.7 | NL | NL | NL | NL | NL | |
|
| 3.5 | 1.7 | NL | NL | NL | NL | NL | |
|
| 3.5 | 1.6 | NL | NL | NL | NL | NL | |
|
| 2.0 | 1.4 | NL | NL | NL | 60 | 60 | |
|
| Conventional construction |
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|
|
|
|
|
|
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| Moment-resisting frames | 1.5 | 1.3 | NL | NL | 15 | NP | NP |
|
| Shear walls | 1.5 | 1.3 | NL | NL | 40 | 30 | 30 |
|
| Other concrete SFRS(s) not listed above | 1.0 | 1.0 | 15 | 15 | NP | NP | NP |
| 3. | Timber Structures designed and Detailed According to CSA O86 |
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| ||
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| Shear walls |
|
|
|
|
|
|
|
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| 3.0 | 1.7 | NL | NL | 30 | 20 | 20 | |
|
| 2.0 | 1.7 | NL | NL | 20 | 20 | 20 | |
|
| Braced or moment-resisting frames with ductile connections |
|
|
|
|
|
|
|
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| Moderately ductile | 2.0 | 1.5 | NL | NL | 20 | 20 | 20 |
|
| Limited ductility | 1.5 | 1.5 | NL | NL | 15 | 15 | 15 |
|
| 1.0 | 1.0 | 15 | 15 | NP | NP | NP | |
| 4. | masonry Structures designed and Detailed According to CSA S304.1 |
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|
|
| |||
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| 2.0 | 1.5 | NL | NL | 60 | 40 | 40 | |
|
| Limited ductility shear walls | 1.5 | 1.5 | NL | NL | 40 | 30 | 30 |
|
| Conventional construction |
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| Shear walls | 1.5 | 1.5 | NL | 60 | 30 | 15 | 15 |
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| Moment-resisting frames | 1.5 | 1.5 | NL | 30 | NP | NP | NP |
|
| Unreinforced masonry | 1.0 | 1.0 | 30 | 15 | NP | NP | NP |
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| Other masonry SFRS(s) not listed above | 1.0 | 1.0 | 15 | NP | NP | NP | NP |
| 5. | Cold-Formed Steel Structures designed and Detailed According to CAN/CSA-S136 |
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| ||||
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| Shear walls |
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|
|
|
|
|
|
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| 2.5 | 1.7 | 20 | 20 | 20 | 20 | 20 | |
|
| Screw-connected shear walls - wood-based and gypsum panels in combination | 1.5 | 1.7 | 20 | 20 | 20 | 20 | 20 |
|
| Diagonal strap concentrically braced walls |
|
|
|
|
|
|
|
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| Limited ductility | 1.9 | 1.3 | 20 | 20 | 20 | 20 | 20 |
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| Conventional construction | 1.2 | 1.3 | 15 | 15 | NP | NP | NP |
|
| Other cold-formed SFRS(s) not listed above | 1.0 | 1.0 | 15 | 15 | NP | NP | NP |
Notes to Table 4.1.8.9.:
(1) See Article 4.1.8.10.
(2) NP = system is not permitted.
NL = system is permitted and not limited in height as an SFRS; height may be limited in other Parts of the Code.
Numbers in columns 4 to 8 are maximum height limits in m.
The most stringent requirement governs.
(3) Higher design force levels are prescribed in CSA S16 for some heights of buildings.