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 R_d and R_o 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 R_d is required by this Article, the corresponding R_o shall be used.

(3)

For combinations of different types of SFRS acting in the same direction in the same storey, R_d R_o shall be taken as the lowest value of R_d R_o corresponding to these systems.

(4)

For vertical variations of R_d R_o, excluding rooftop structures not exceeding two storeys in height whose weight is less than the greater of 10% of W and 30% of W_i of the level below, the value of R_d R_o used in the design of any storey shall be less than or equal to the lowest value of R_d R_o 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 R_d and R_o 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, R_d, Overstrength-Related Force Modification Factors, R_o, 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)

Forming Part of Sentences [[b-4.1.8.9.#^1hplca|4.1.8.9.(1)]] and [[b-4.1.8.9.#^5hplca|(5)]], [[b-4.1.8.10.#^5hplca|4.1.8.10.(5)]] and (6), [[b-4.1.8.11.#^12hplca|4.1.8.11.(12)]], [[b-4.1.8.15.#^9hplca|4.1.8.15.(9)]] and [[b-4.1.8.20.#^8hplca|4.1.8.20.(8)]]

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 I_E S(1.0) ≤ 0.3.

(7) Frames are limited to a maximum of 3 storeys.