4.1.8.9.Force Reduction Factors, System Overstrength Factors, and General

Restrictions (1) Except as provided in Articles 4.1.8.20. and 4.1.8.22., 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 value 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.(6) must be satisfied. (See Note A-4.1.8.9.(4)) (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 defined 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. (See Note A-4.1.8.9.(5)) 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 Sentences 4.1.8.9.(1) and (5), 4.1.8.10.(5) and (6), 4.1.8.11.(12), 4.1.8.15.(9) and 4.1.8.20.(8) Restrictions(2) Type of SFRS Rd Ro Seismic Category SC1 SC2 SC3 SC4 Steel Structures Designed and Detailed According to CSA S16(3)(4) Ductile moment-resisting frames 5.0 1.5 NL NL NL NL Moderately ductile moment-resisting frames 3.5 1.5 NL NL NL NL Limited ductility moment-resisting frames 2.0 1.3 NL NL 60 30 Moderately ductile truss moment-resisting frames 3.5 1.6 NL NL 50 30 Moderately ductile concentrically braced frames Tension-compression braces 3.0 1.3 NL NL 40 40 Tension only braces 3.0 1.3 NL NL 20 20 Limited ductility concentrically braced frames Tension-compression braces 2.0 1.3 NL NL 60 60 Tension only braces 2.0 1.3 NL NL 40 40 Ductile buckling-restrained braced frames 4.0 1.2 NL NL 40 40 Ductile eccentrically braced frames 4.0 1.5 NL NL NL NL Ductile plate walls 5.0 1.6 NL NL NL NL Moderately ductile plate walls 3.5 1.3 NL NL 40 40 Limited ductility plate walls 2.0 1.5 NL NL 60 60 Conventional construction of moment-resisting frames, braced frames or plate walls Assembly occupancies 1.5 1.3 NL NL 15 15 Other occupancies 1.5 1.3 NL NL 60 40 Other steel SFRS(s) not defined above 1.0 1.0 15 15 NP NP Concrete Structures Designed and Detailed According to CSA A23.3 Ductile moment-resisting frames 4.0 1.7 NL NL NL NL Moderately ductile moment-resisting frames 2.5 1.4 NL NL 60 40 Ductile coupled walls 4.0 1.7 NL NL NL NL Moderately ductile coupled walls 2.5 1.4 NL NL NL 60 Ductile partially coupled walls 3.5 1.7 NL NL NL NL Moderately ductile partially coupled walls 2.0 1.4 NL NL NL 60 Ductile shear walls 3.5 1.6 NL NL NL NL Moderately ductile shear walls 2.0 1.4 NL NL NL 60 Conventional construction Moment-resisting frames 1.5 1.3 NL NL 20 10(5)(6) Shear walls 1.5 1.3 NL NL 40 30 Two-way slabs without beams 1.3 1.3 20 15 NP NP Tilt-up Construction Moderately ductile walls and frames 2.0 1.3 30 25 25 25 Limited ductility walls and frames 1.5 1.3 30 25 20 20(7) Conventional walls and frames 1.3 1.3 25 20 NP NP Other concrete SFRS(s) not listed above 1.0 1.0 15 15 NP NP Table 4.1.8.9. (Cont’d) SFRS Ductility-Related Force Modification Factors, Rd, Overstrength-Related Force Modification Factors, Ro, and General Restrictions(1) Forming Part of Sentences 4.1.8.9.(1) and (5), 4.1.8.10.(5) and (6), 4.1.8.11.(12), 4.1.8.15.(9) and 4.1.8.20.(8) Restrictions(2) Type of SFRS Rd Ro Seismic Category SC1 SC2 SC3 SC4 Timber Structures Designed and Detailed According to CSA O86 Shear walls Nailed shear walls: wood-based panel 3.0 1.7 NL NL 30 20 Shear walls: wood-based and gypsum panels in 2.0 1.7 NL NL 20 20 combination Moderately ductile cross-laminated timber shear 2.0 1.5 30 30 30 20 walls: platform-type construction Limited ductility cross-laminated timber shear 1.0 1.3 30 30 30 20 walls: platform-type construction Braced or moment-resisting frames with ductile connections Moderately ductile 2.0 1.5 NL NL 20 20 Limited ductility 1.5 1.5 NL NL 15 15 Other wood- or gypsum-based SFRS(s) not listed above 1.0 1.0 15 15 NP NP Masonry Structures Designed and Detailed According to CSA S304 Ductile shear walls 3.0 1.5 NL NL 60 40 Moderately ductile shear walls 2.0 1.5 NL NL 60 40 Conventional construction Shear walls 1.5 1.5 NL 60 30 15 Moment-resisting frames 1.5 1.5 NL 30 NP NP Unreinforced masonry 1.0 1.0 30 15 NP NP Other masonry SFRS(s) not listed above 1.0 1.0 15 NP NP NP Cold-Formed Steel Structures Designed and Detailed According to CSA S136 Shear walls Screw-connected shear walls - wood-based panels 2.5 1.7 20 20 20 20 Screw-connected shear walls - wood-based and 1.5 1.7 20 20 20 20 gypsum panels in combination Diagonal strap concentrically braced walls Limited ductility 1.9 1.3 20 20 20 20 Conventional construction 1.2 1.3 15 15 NP NP Other cold-formed SFRSs not listed above 1.0 1.0 15 15 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. Numbers in this Table are maximum height limits above grade, in m. Height may be limited in other Parts of the Code. The most stringent requirement governs. (3) Higher design force levels are prescribed in CSA S16 for some heights of buildings. (4) See Note A-Table 4.1.8.9. (5) Frames are limited to a maximum of 2 storeys. (6) The maximum height limit is permitted to be increased to 15 m where IES(1.0) ≤ 0.3. (7) Frames are limited to a maximum of 3 storeys.