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// CODE SNIPPET

2305.2 Design of Wood Diaphragms

2010 Building Code of NY > 23 Wood > 2305 General Design Requirements for Lateral-Force-Resisting Systems > 2305.2 Design of Wood Diaphragms
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2305.2.1 General

Wood diaphragms are permitted to be used to resist horizontal forces provided the deflection in the plane of the diaphragm, as determined by calculations, tests or analogies drawn therefrom, does not exceed the permissible deflection of attached distributing or resisting elements. Connections shall extend into the diaphragm a sufficient distance to develop the force transferred into the diaphragm.

2305.2.2 Deflection

Permissible deflection shall be that deflection up to which the diaphragm and any attached distributing or resisting element will maintain its structural integrity under design load conditions, such that the resisting element will continue to support design loads without danger to occupants of the structure. Calculations for diaphragm deflection shall account for the usual bending and shear components as well as any other factors, such as nail deformation, which will contribute to deflection.

The deflection (Δ) of a blocked wood structural panel diaphragm uniformly nailed throughout is permitted to be calculated by using the following equation. If not uniformly nailed, the constant 0.188 (For SI: 1/1627) in the third term must be modified accordingly.

 (Equation 23-1)

For SI:
where:

A
= Area of chord cross section, in square inches (mm2).

b
= Diaphragm width, in feet (mm).

E
= Elastic modulus of chords, in pounds per square inch (N/mm2).

e
n = Nail or staple deformation, in inches (mm) [see Table 2305.2.2(1)].

Gt =
Panel rigidity through the thickness, in pounds per inch (N/mm) of panel width or depth [see Table 2305.2.2(2)].

L
= Diaphragm length, in feet (mm).

v
= Maximum shear due to design loads in the direction under consideration, in pounds per linear foot (plf) (N/mm).

Δ = The calculated deflection, in inches (mm).

Σ (ΔcX) = Sum of individual chord-splice slip values on both sides of the diaphragm, each multiplied by its distance to the nearest support.

TABLE 2305.2.2(1)
en VALUES (inches) FOR USE IN CALCULATING DIAPHRAGM DEFLECTION DUE TO FASTENER SLIP (Structural I)a,d
LOAD PER FASTENERc (pounds) FASTENER DESIGNATIONSb
6d 8d 10d 14-Ga staple × 2
inches long
60 0.01 0.00 0.00 0.011
80 0.02 0.01 0.01 0.018
100 0.03 0.01 0.01 0.028
120 0.04 0.02 0.01 0.04
140 0.06 0.03 0.02 0.053
160 0.10 0.04 0.02 0.068
180 — 0.05 0.03 —
200 — 0.07 0.47 —
220 — 0.09 0.06 —
240 — — 0.07 —

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound = 4.448 N.
  1. Increase en values 20 percent for plywood grades other than Structural I.
  2. Nail values apply to common wire nails or staples identified.
  3. Load per fastener = maximum shear per foot divided by the number of fasteners per foot at interior panel edges.
  4. Decrease en values 50 percent for seasoned lumber (moisture content < 19 percent).
TABLE 2305.2.2(2)
VALUES OF Gt FOR USE IN CALCULATING DEFLECTION OF WOOD STRUCTURAL PANEL SHEAR WALLS AND DIAPHRAGMS
PANEL TYPE SPAN RATING VALUES OF Gt (lb/in. panel depth or width)
OTHER STRUCTURAL I
3-ply Plywood 4-ply Plywood 5-ply Plywooda OSB 3-ply Plywood 4-ply Plywood 5-ply Plywooda OSB
Sheathing 24/0 25,000 32,500 37,500 77,500 32,500 42,500 41,500 77,500
24/16 27,000 35,000 40,500 83,500 35,000 45,500 44,500 83,500
32/16 27,000 35,000 40,500 83,500 35,000 45,500 44,500 83,500
40/20 28,500 37,000 43,000 88,500 37,000 48,000 47,500 88,500
48/24 31,000 40,500 46,500 96,000 40,500 52,500 51,000 96,000
Single Floor 16 o.c. 27,000 35,000 40,500 83,500 35,000 45,500 44,500 83,500
20 o.c. 28,000 36,500 42,000 87,000 36,500 47,500 46,000 87,000
24 o.c. 30,000 39,000 45,000 93,000 39,000 50,500 49,500 93,000
32 o.c. 36,000 47,000 54,000 110,000 47,000 61,000 59,500 110,000
48 o.c. 50,500 65,500 76,000 155,000 65,500 85,000 83,500 155,000


    OTHER STRUCTURAL I
Thickness (in.) A-A, A-C Marine All Other
Grades
A-A, A-C Marine All Other Grades
Sanded Plywood 1/4 24,000 31,000 24,000 31,000 31,000 31,000
11/32 25,500 33,000 25,500 33,000 33,000 33,000
3/8 26,000 34,000 26,000 34,000 34,000 34,000
15/32 38,000 49,500 38,000 49,500 49,500 49,500
1/2 38,500 50,000 38,500 50,000 50,000 50,000
19/32 49,000 63,500 49,000 63,500 63,500 63,500
5/8 49,500 64,500 49,500 64,500 64,500 64,500
23/32 50,500 65,500 50,500 65,500 65,500 65,500
3/4 51,000 66,500 51,000 66,500 66,500 66,500
7/8 52,500 68,500 52,500 68,500 68,500 68,500
1 73,500 95,500 73,500 95,500 95,500 95,500
11/8 75,000 97,500 75,000 97,500 97,500 97,500

For SI: 1 inch = 25.4 mm, 1 pound/inch = 0.1751 N/mm.
  1. Applies to plywood with five or more layers; for five-ply/three-layer plywood, use values for four ply.

2305.2.3 Diaphragm Aspect Ratios

Size and shape of diaphragms shall be limited as set forth in Table 2305.2.3.

TABLE 2305.2.3
MAXIMUM DIAPHRAGM DIMENSION RATIOS
HORIZONTAL AND SLOPED DIAPHRAGM
TYPE MAXIMUM LENGTH - WIDTH RATIO
Wood structural panel, nailed all edges 4:1
Wood structural panel, blocking omitted at intermediate joints 3:1
Diagonal sheathing, single 3:1
Diagonal sheathing, double 4:1

2305.2.4 Construction

Wood diaphragms shall be constructed of wood structural panels manufactured with exterior glue and not less than 4 feet by 8 feet (1219 mm by 2438 mm), except at boundaries and changes in framing where minimum sheet dimension shall be 24 inches (610 mm) unless all edges of the undersized sheets are supported by and fastened to framing members or blocking.

Wood structural panel thickness for horizontal diaphragms shall not be less than the valves set forth in Tables 2304.7(3), 2304.7(4) and 2304.7(5) for corresponding joist spacing and loads.

2305.2.4.1 Seismic Design Category F

Structures assigned to Seismic Design Category F shall conform to the additional requirements of this section.

Wood structural panel sheathing used for diaphragms and shear walls that are part of the seismic-force-resisting system shall be applied directly to the framing members.

Exception: Wood structural panel sheathing in a diaphragm is permitted to be fastened over solid lumber planking or laminated decking, provided the panel joints and lumber planking or laminated decking joints do not coincide.

2305.2.5 Rigid Diaphragms

Design of structures with rigid diaphragms shall conform to the structure configuration requirements of Section 12.3.2 of ASCE 7 and the horizontal shear distribution requirements of Section 12.8.4 of ASCE 7.

Open-front structures with rigid wood diaphragms resulting in torsional force distribution are permitted, provided the length, l, of the diaphragm normal to the open side does not exceed 25 feet (7620 mm), the diaphragm sheathing conforms to Section 2305.2.4 and the l/w ratio [as shown in Figure 2305.2.5(1)] is less than 1 for one-story structures or 0.67 for structures over one story in height.

Exception: Where calculations show that diaphragm deflections can be tolerated, the length, l, normal to the open end is permitted to be increased to a l/w ratio not greater than 1.5 where sheathed in compliance with Section 2305.2.4 or to 1 where sheathed in compliance with Section 2306.3.4 or 2306.3.5.

Rigid wood diaphragms are permitted to cantilever past the outermost supporting shearwall (or other vertical resisting element) a length, l, of not more than 25 feet (7620 mm) or two-thirds of the diaphragm width, w, whichever is smaller. Figure 2305.2.5(2) illustrates the dimensions of l and w for a cantilevered diaphragm.

Structures with rigid wood diaphragms having a torsional irregularity in accordance with Table 12.3-1, Item 1, of ASCE 7 shall meet the following requirements: the l/w ratio shall not exceed 1 for one-story structures or 0.67 for structures over one story in height, where l is the dimension parallel to the load direction for which the irregularity exists.

Exception: Where calculations demonstrate that the diaphragm deflections can be tolerated, the width is permitted to be increased and the l/w ratio is permitted to be increased to 1.5 where sheathed in compliance with Section 2305.2.4 or 1 where sheathed in compliance with Section 2306.3.4 or 2306.3.5.

FIGURE 2305.2.5(1)
DIAPHRAGM LENGTH AND WIDTH FOR PLAN VIEW OF OPEN-FRONT BUILDING

FIGURE 2305.2.5(2)
DIAPHRAGM LENGTH AND WIDTH FOR PLAN VIEW OF CANTILEVERED DIAPHRAGM

Related Code Sections


2305.2 Wood, Design of Wood Diaphragms
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2010 Building Code of NY > 23 Wood > 2305 General Design Requirements for Lateral-Force-Resisting Systems > 2305.2 Design of Wood Diaphragms
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Structures assigned to Seismic Design Category F shall conform to the additional requirements of this section. Wood structural panel sheathing ...
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