Proposed Change 1901

1901

Page: Last modified: 2024-02-08

Problem

The formula in Sentence 4.1.8.18.(1) of Division B of the NBC for the determination of the specified lateral earthquake force, V_p, on an element or component of a building provides incorrect results and, in some cases, unconservative design forces.

The formula is also inconsistent with those in standards used in other jurisdictions, such as ASCE and Eurocode standards. The force determined using the formula in the NBC may be either lower or higher than the actual estimated value.

In cases where the Code-calculated force is lower, the risk to life safety and risk of injury from the potential failure of the connection between the element or component and the structure are increased. In cases where the force is higher, unnecessary conservatism is introduced in the design of connections.

Justification

Sentence 4.1.8.18.(1) provides a formula for the determination of the lateral earthquake force, V_p, used to design the connections between structures and elements of structures, non-structural components and equipment. The current formula provides an unconservative value of the force for the design of connections in some cases. Such connections may fail in an earthquake.

A failure of the connections between elements and components and the structure poses significant risk to the safety of the building occupants and people in the vicinity of the building. In addition, past studies have indicated that damage from the failure of elements of structures and non-structural components is a major contributing factor to the overall impact of an earthquake. On the other hand, the formula provides overly conservative results in some cases, which may increase the cost of connections.

The proposed use of peak ground acceleration in the formula in Sentence 4.1.8.18.(1) instead of design spectral acceleration provides a value of V_p that is closer to its expected value in an earthquake. This change would, on one hand, mitigate the increased risk to life safety and higher probability of injury and, on the other hand, address the conservatism in the current requirement.

PROPOSED CHANGE

[4.1.8.18.] 4.1.8.18.Elements of Structures, Non-structural Components and Equipment

(See Note A-4.1.8.18.PROPOSED CHANGE A-4.1.8.18.)

[1] 1)Except as provided in Sentences (2), (7) and (16), elements and components of buildings described in Table 4.1.8.18. and their connections to the structure shall be designed to accommodate the building deflections calculated in accordance with Article 4.1.8.13. and the element or component deflections calculated in accordance with Sentence (9), and shall be designed for a specified lateral earthquake force, V_p, distributed according to the distribution of mass:

~~$V_{p} = 0.3 S (0.2) I_{E} S_{p} W_{p}$~~

V_{p} = PGA (X) I_{E} S_{P} W_{P}

where

~~S(0.2)~~

~~= design spectral acceleration value at a period of ~~0.2 s~~, as defined in ~~Sentence 4.1.8.4.(6)~~,~~

PGA(X)

= peak ground acceleration, expressed as a ratio to gravitational acceleration, for site designation X, as defined in Sentence 4.1.8.4.(1),

I_E

= earthquake importance factor for the building, as defined in Article 4.1.8.5.,

~~S_p~~

~~= C_pA_rA_x/R_p (the maximum value of S_p shall be taken as 4.0 and the minimum value of S_p shall be taken as 0.7), where~~

~~C_p = element or component factor from ~~Table 4.1.8.18.~~,~~

~~A_r = element or component force amplification factor from ~~Table 4.1.8.18.~~,~~

~~A_x = height factor (1 + 2h_x/h_n),~~

~~R_p = element or component response modification factor from ~~Table 4.1.8.18.~~, and~~

W_p

= weight of the component or element, and.

S_p

= horizontal force factor for the element or component and its connection, and

= C_pA_rA_x/R_p, but not less than 0.7 and not greater than 4.0,

where

C_p

= element or component factor, as provided in Table 4.1.8.18.,

A_r

= element or component force amplification factor, as provided in Table 4.1.8.18.,

R_p

= element or component response modification factor, as provided in Table 4.1.8.18., and

A_x

= height factor at level x to account for variation of response of the element or component with elevation within the building,

= 1 where the component or element is located at or below ground level, and

= 1 + 2.5 \frac{h_{x}}{h_{n}} or \frac{1 + \frac{1}{T_{ao}} (\frac{h_{x}}{h_{n}}) + {(1 - \frac{0.4}{T_{ao}})}^{2} {(\frac{h_{x}}{h_{n}})}^{10}}{\sqrt{\frac{1.1 R_{do}}{I_{E}}}} otherwise,

where

T_ao

= lowest fundamental lateral period of the building, as defined in Sentence 4.1.8.11.(3), in either orthogonal direction, but not less than 0.4, and

R_do

= ductility-related force modification factor of the building, as defined in Article 4.1.8.9., in the same orthogonal direction as T_ao, and

= 1.0 for the purposes of Article 4.1.8.23.

Table [4.1.8.18.] 4.1.8.18.
Elements of Structures and Non-structural Components and Equipment^{PROPOSED CHANGE Table 4.1.8.18. Footnote (1)}
Forming Part of Sentences [4.1.8.18.] 4.1.8.18.([1] 1) to ([3] 3), ([6] 6), ([7] 7) and ([16] 16), and Clauses 4.1.8.23.(2)(c) and (3)(c)
Category	Part or Portion of Building	C_p	A_r	R_p
Architectural and Structural Components
1	All exterior and interior walls, and cladding panels, except those in Category 2 or 3	1.00	1.00	2.50
2	Cantilever parapet and other cantilever walls, including cantilever cladding panels, except retaining walls	1.00	2.50	2.50
3	Exterior and interior ornamentations and appendages	1.00	2.50	2.50
4	Floors and roofs acting as diaphragms^{PROPOSED CHANGE Table 4.1.8.18. Footnote (2)}	–	–	–
5	Towers, chimneys, smokestacks and penthouses when connected to or forming part of a building	1.00	2.50	2.50
6	Horizontally cantilevered floors, balconies, beams, etc.	1.00	1.00	2.50
7	Suspended ceilings, light fixtures and other attachments to ceilings with independent vertical support	1.00	1.00	2.50
8	Masonry veneer connections	1.00	1.00	1.50
9	Access floors	1.00	1.00	2.50
10	Masonry or concrete fences more than 1.8 m tall	1.00	1.00	2.50
Mechanical and Electrical Components
11	Machinery, fixtures, equipment and tanks (including contents)
	that are rigid and rigidly connected	1.00	1.00	1.25
	that are flexible or flexibly connected	1.00	2.50	2.50
12	Machinery, fixtures, equipment and tanks (including contents) containing toxic or explosive materials, materials having a flash point below 38°C or firefighting fluids
	that are rigid and rigidly connected	1.50	1.00	1.25
	that are flexible or flexibly connected	1.50	2.50	2.50
13	Flat bottom tanks (including contents) attached directly to a floor at or below grade within a building	0.70	1.00	2.50
14	Flat bottom tanks (including contents) attached directly to a floor at or below grade within a building containing toxic or explosive materials, materials having a flash point below 38°C or firefighting fluids	1.00	1.00	2.50
15	Pipes, ducts (including contents)	1.00	1.00	3.00
16	Pipes, ducts (including contents) containing toxic or explosive materials	1.50	1.00	3.00
17	Electrical cable trays, bus ducts, conduits	1.00	2.50	5.00
Other System Components
18	Rigid components with ductile material and connections	1.00	1.00	2.50
19	Rigid components with non-ductile material or connections	1.00	1.00	1.00
20	Flexible components with ductile material and connections	1.00	2.50	2.50
21	Flexible components with non-ductile material or connections	1.00	2.50	1.00
22	Elevators and escalators^{PROPOSED CHANGE Table 4.1.8.18. Footnote (3)}
	machinery and equipment	as per Category 11
	elevator rails	1.00	1.00	2.50
23	Floor-mounted steel pallet storage racks^{PROPOSED CHANGE Table 4.1.8.18. Footnote (4)}	1.00	2.50	2.50
24	Floor-mounted steel pallet storage racks on which are stored toxic or explosive materials or materials having a flash point below 38°C^{PROPOSED CHANGE Table 4.1.8.18. Footnote (4)}	1.50	2.50	2.50

[2] 2)For buildings in Seismic Category SC1 or SC2, other than post-disaster buildings, seismically isolated buildings, and buildings with supplemental energy dissipation systems, the requirements of Sentence (1) need not apply to Categories 6 through 22 of Table 4.1.8.18.

[3] 3)For the purpose of applying Sentence (1) for Categories 11 and 12 of Table 4.1.8.18., elements or components shall be assumed to be flexible or flexibly connected unless it can be shown that the fundamental period of the element or component and its connection is less than or equal to 0.06 s, in which case the element or component is classified as being rigid and rigidly connected.

[4] 4)The weight of access floors shall include the dead load of the access floor and the weight of permanent equipment, which shall not be taken as less than 25% of the floor live load.

[5] 5)When the mass of a tank plus its contents or the mass of a flexible or flexibly connected piece of machinery, fixture or equipment is greater than 10% of the mass of the supporting floor, the lateral forces shall be determined by rational analysis.

[6] 6)Forces shall be applied in the horizontal direction that results in the most critical loading for design, except for Category 6 of Table 4.1.8.18., where the forces shall be applied up and down vertically.

[7] 7)Connections to the structure of elements and components listed in Table 4.1.8.18. shall be designed to support the component or element for gravity loads, shall conform to the requirements of Sentence (1), and shall also satisfy these additional requirements:

[a] a)except as provided in Sentence (17), friction due to gravity loads shall not be considered to provide resistance to earthquake forces,

[b] b)R_p for non-ductile connections, such as adhesives or power-actuated fasteners, shall be taken as 1.0,

[c] c)R_p for shallow post-installed mechanical, post-installed adhesive, and cast-in-place anchors in concrete shall be 1.5, where shallow anchors are those with a ratio of embedment length to diameter of less than 8,

[d] d)post-installed mechanical, drop-in and adhesive anchors in concrete shall be pre-qualified for seismic applications by cyclic load testing in accordance with

[i] i)CSA A23.3, "Design of concrete structures", and

[ii] ii)ACI 355.2, "Qualification of Post-Installed Mechanical Anchors in Concrete (ACI 355.2-19) and Commentary", or ACI 355.4, "Qualification of Post-Installed Adhesive Anchors in Concrete (ACI 355.4-19) and Commentary", as applicable,

[e] e)post-installed mechanical and adhesive anchors in masonry and post-installed mechanical anchors in structural steel shall be pre-qualified for seismic applications by cyclic tension load testing (see Note A-4.1.8.18.(7)(e)PROPOSED CHANGE A-4.1.8.18.(7)(e)),

[f] f)power-actuated fasteners shall not be used for cyclic tension loads,

[g] g)connections for non-structural elements or components of Category 1, 2 or 3 of Table 4.1.8.18. attached to the side of a building and above the first level above grade shall satisfy the following requirements:

[i] i)for connections where the body of the connection is ductile, the body shall be designed for values of C_p, A_r and R_p given in Table 4.1.8.18., and all of the other parts of the connection, such as anchors, welds, bolts and inserts, shall be capable of developing 2.0 times the nominal yield resistance of the body of the connection, and

[ii] ii)connections where the body of the connection is not ductile shall be designed for values of C_p = 2.0, R_p = 1.0 and A_r given in Table 4.1.8.18., and

[h] h)a ductile connection is one where the body of the connection is capable of dissipating energy through cyclic inelastic behaviour.

[8] 8)Floors and roofs acting as diaphragms shall satisfy the requirements for diaphragms stated in Article 4.1.8.15.

[9] 9)Lateral deflections of elements or components shall be based on the loads defined in Sentence (1) and lateral deflections obtained from an elastic analysis shall be multiplied by R_p/I_E to give realistic values of the anticipated deflections.

[10] 10)The elements or components shall be designed so as not to transfer to the structure any forces unaccounted for in the design, and rigid elements such as walls or panels shall satisfy the requirements of Sentence 4.1.8.3.(6).

[11] 11)Seismic restraint for suspended equipment, pipes, ducts, electrical cable trays, etc. shall be designed to meet the force and displacement requirements of this Article and be constructed in a manner that will not subject hanger rods to bending.

[12] 12)Isolated suspended equipment and components, such as pendent lights, may be designed as a pendulum system provided that adequate chains or cables capable of supporting 2.0 times the weight of the suspended component are provided and the deflection requirements of Sentence (10) are satisfied.

[13] 13)Free-standing steel pallet storage racks are permitted to be designed to resist earthquake effects using rational analysis, provided the design achieves the minimum performance level required by Subsection 4.1.8. (See Note A-4.1.8.18.(13) and 4.4.3.1.(1)PROPOSED CHANGE A-4.1.8.18.(13) and 4.4.3.1.(1).)

[14] 14)Except as provided in Sentence (15), the relative displacement of glass in glazing systems, D_fallout, shall be equal to the greater of

[a] a)D_fallout ≥ 1.25I_ED_p, where

D_fallout

= relative displacement at which glass fallout occurs, and

D_p

= relative earthquake displacement that the component must be designed to accommodate, calculated in accordance with Article 4.1.8.13. and applied over the height of the glass component, or

[b] b)13 mm.

(See Note A-4.1.8.18.(14) and (15)PROPOSED CHANGE A-4.1.8.18.(14) and (15).)

[15] 15)Glass need not comply with Sentence (14), provided at least one of the following conditions is met:

[a] a)the Seismic Category is SC1 or SC2,

[b] b)the glass has sufficient clearance from its frame such that D_clear ≥ 1.25D_p calculated as follows:

D_{clear} = 2 C_{1} (1 + \frac{h_{p} C_{2}}{b_{p} C_{1}})

where

D_clear

= relative horizontal displacement measured over the height of the glass panel, which causes initial glass-to-frame contact,

C₁

= average of the clearances on both sides between the vertical glass edges and the frame,

h_p

= height of the rectangular glass panel,

C₂

= averages of the top and bottom clearances between the horizontal glass edges and the frame, and

b_p

= width of the rectangular glass panel,

[c] c)the glass is fully tempered, monolithic, installed in a non-post-disaster building, and no part of the glass is located more than 3 m above a walking surface, or

[d] d)the glass is annealed or heat-strengthened laminated glass in a single thickness with an interlayer no less than 0.76 mm and captured mechanically in a wall system glazing pocket with the perimeter secured to the frame by a wet, glazed, gunable, curing, elastomeric sealant perimeter bead of 13 mm minimum glass contact width.

(See Note A-4.1.8.18.(14) and (15)PROPOSED CHANGE A-4.1.8.18.(14) and (15).)

[16] 16)~~For structures with supplemental energy dissipation,~~Notwithstanding the requirements in the remainder of this Article, elements and components of buildings described in Table 4.1.8.18. and their connections to the structure ~~shall~~are permitted to be designed for a specified lateral earthquake force, V_p, determined at each floor level using a Non-linear Dynamic Analysis performed in accordance with Article 4.1.8.12., as follows:

V_{p} = S_{sed} I_{E} (\frac{C_{p} A_{r}}{R_{p}}) W_{p}

where

S_sed

= peak spectral acceleration, S_a(T,X), in the period range of T = 0 s to T = 0.5 s determined from the mean 5%-damped floor spectral acceleration values by averaging the individual 5%-damped floor response spectra at the centroid of the floor area at that floor level ~~determined using Non-linear Dynamic Analysis~~, and

I_E, C_p, A_r, R_p, W_p

= as defined in Sentence (1).

(See Note A-4.1.8.18.(16)PROPOSED CHANGE A-4.1.8.18.(16).)

[17] 17)For a ballasted array of interconnected solar panels mounted on a roof, where I_ES(0.2) is less than or equal to 1.0, friction due to gravity loads is permitted to be considered to provide resistance to seismic forces, provided

[a] a)the roof is not normally occupied,

[b] b)the roof is surrounded by a parapet extending from the roof surface to not less than the greater of

[i] i)150 mm above the centre of mass of the array, and

[ii] ii)400 mm above the roof surface,

[c] c)the height of the centre of mass of the array above the roof surface is less than the lesser of

[i] i)900 mm, and

[ii] ii)one half of the smallest plan dimension of the supporting base of the array,

[d] d)the roof slope at the location of the array is less than or equal to 3°,

[e] e)the factored friction resistance calculated using the kinetic friction coefficient determined in accordance with Sentence (18) and a resistance factor of 0.7 is greater than or equal to the specified lateral earthquake force, V_p, on the array determined in accordance with Sentence (1) using values of A_r = 1.0, A_x = 3.0, C_p = 1.0, and R_p = 1.25,

[f] f)the minimum clearance between the array and other arrays or fixed objects is the greater of

[i] i)225 mm, and

[ii] ii)1 500(I_ES(0.2) − 0.4)², in mm, and

[g] g)the minimum clearance between the array and the roof parapet is the greater of

[i] i)450 mm, and

[ii] ii)3 000(I_ES(0.2) − 0.4)², in mm.

[18] 18)For the purpose of Clause (17)(e), the kinetic friction coefficient shall be determined in accordance with ASTM G115, "Standard Guide for Measuring and Reporting Friction Coefficients", through experimental testing that

[a] a)is carried out by an accredited laboratory on a full-scale array or a prototype of the array,

[b] b)models the interface between the supporting base of the array and the roof surface, and

[c] c)accounts for the adverse effects of anticipated climatic conditions on the friction resistance.

(See Note A-4.1.8.18.(18)PROPOSED CHANGE A-4.1.8.18.(18).)

Note A-4.1.8.18.(16) Elements of Structures, Non-structural Components and Equipment in Structures with Supplemental Energy DissipationDesign Using Non-linear Dynamic Analysis.

Information on the requirements of Sentence 4.1.8.18.(16) can be found in the Commentary entitled Design for Seismic Effects in the "Structural Commentaries (User's Guide – NBC 2020: Part 4 of Division B)".

Impact analysis

The proposed change would not have a major impact on the design practice for and cost of connections for elements of structures and non-structural components. Modifications are proposed to an existing formula in Sentence 4.1.8.18.(1) for calculation of the specified lateral earthquake force, V_p. The triggers that determine the application of the Code requirements are not changed.

The cost impact of the change is expected to be very low. In most cases, the increase in V_p due to the use of peak ground acceleration in the formula is reduced by the decrease in V_p due to the use of the modified expression for the height factor, A_x.

On average, the increase in V_p is about 18%. The resulting increase in the overall cost of construction would be less than 0.05%.

Enforcement implications

The proposed change would have minimal enforcement implications, as it modifies existing formulae in the Code. The value of peak ground acceleration, which is proposed to be used in the formula for the specified lateral earthquake force, V_p, instead of design spectral acceleration, is provided by the NBC. The existing formula for the height factor, A_x, is retained to provide an option for Code users who do not want to use the new formula for A_x, which reduces the forces but is more complex.

The triggers for the application of the Code requirements are not changed. Code users would need to become familiar with the new formulae, but the proposed change would not involve a significant change in practice. Therefore, no difficulties are expected to be encountered in applying the change.

Who is affected

Owners, architects, designers, contractors and enforcement professionals dealing with the design of connections for elements of structures, non-structural components and equipment in large (Part 4) buildings.

OBJECTIVE-BASED ANALYSIS OF NEW OR CHANGED PROVISIONS

[4.1.8.18.] 4.1.8.18. ([1] 1) [F20,F22-OS2.4]

[4.1.8.18.] 4.1.8.18. ([1] 1) [F20-OP2.3][F22-OP2.3,OP2.4]

[4.1.8.18.] 4.1.8.18. ([2] 2) no attributions

[4.1.8.18.] 4.1.8.18. ([3] 3) no attributions

[4.1.8.18.] 4.1.8.18. ([4] 4) [F20,F22-OS2.4]

[4.1.8.18.] 4.1.8.18. ([4] 4) [F20,F22-OP2.3,OP2.4]

[4.1.8.18.] 4.1.8.18. ([5] 5) [F20,F22-OS2.1]

[4.1.8.18.] 4.1.8.18. ([5] 5) [F20,F22-OP2.1,OP2.4]

[4.1.8.18.] 4.1.8.18. ([6] 6) [F20,F22-OS2.4]

[4.1.8.18.] 4.1.8.18. ([6] 6) [F20,F22-OP2.3,OP2.4]

[4.1.8.18.] 4.1.8.18. ([7] 7) [F20,F22-OS2.4]

[4.1.8.18.] 4.1.8.18. ([7] 7) [F20,F22-OP2.3,OP2.4]

[4.1.8.18.] 4.1.8.18. ([7] 7) ([a] a)[F20,F22-OS2.4]

[4.1.8.18.] 4.1.8.18. ([7] 7) ([a] a)[F20,F22-OP2.3,OP2.4]

[4.1.8.18.] 4.1.8.18. ([7] 7) ([b] b),([c] c)[F20,F22-OS2.4]

[4.1.8.18.] 4.1.8.18. ([7] 7) ([b] b),([c] c)[F20,F22-OP2.3,OP2.4]

[4.1.8.18.] 4.1.8.18. ([7] 7) ([d] d),([f] f)[F20,F22-OS2.4]

[4.1.8.18.] 4.1.8.18. ([7] 7) ([d] d),([f] f)[F20,F22-OP2.3,OP2.4]

[4.1.8.18.] 4.1.8.18. ([7] 7) ([g] g)[F20,F22-OS2.4]

[4.1.8.18.] 4.1.8.18. ([7] 7) ([g] g)[F20,F22-OP2.3,OP2.4]

[4.1.8.18.] 4.1.8.18. ([7] 7) ([h] h)

[4.1.8.18.] 4.1.8.18. ([8] 8) no attributions

[4.1.8.18.] 4.1.8.18. ([9] 9) [F22-OS2.3,OS2.4]

[4.1.8.18.] 4.1.8.18. ([9] 9) [F22-OP2.3,OP2.4]

[4.1.8.18.] 4.1.8.18. ([10] 10) [F22-OS2.1,OS2.3,OS2.4]

[4.1.8.18.] 4.1.8.18. ([10] 10) [F22-OP2.1,OP2.3,OP2.4]

[4.1.8.18.] 4.1.8.18. ([11] 11) [F20-OS2.1][F22-OS2.4]

[4.1.8.18.] 4.1.8.18. ([11] 11) [F20,F22-OP2.3,OP2.4]

[4.1.8.18.] 4.1.8.18. ([12] 12) [F20-OS2.1][F22-OS2.3]

[4.1.8.18.] 4.1.8.18. ([12] 12) [F20-OP2.1][F22-OP2.3]

[4.1.8.18.] 4.1.8.18. ([13] 13) no attributions

[4.1.8.18.] 4.1.8.18. ([14] 14) [F22-OS2.4]

[4.1.8.18.] 4.1.8.18. ([15] 15) no attributions

[4.1.8.18.] 4.1.8.18. ([16] 16) [F20,F22-OS2.4]

[4.1.8.18.] 4.1.8.18. ([16] 16) [F20-OP2.3][F22-OP2.3,OP2.4]

[4.1.8.18.] 4.1.8.18. ([17] 17) no attributions

[4.1.8.18.] 4.1.8.18. ([18] 18) no attributions

Date modified:: 2024-02-08