Code of Massachusetts Regulations
780 CMR - STATE BOARD OF BUILDING REGULATIONS AND STANDARDS
Chapter 23 - Wood
Section 2305 - GENERAL DESIGN REQUIREMENTS FOR LATERAL-FORCE-RESISTING SYSTEMS
Subsection 2305.2 - Diaphragm deflection
The deflection (Delta) of a blocked wood structural panel diaphragm uniformly fastened throughout with staples is permitted to be calculated by using the following equation. If not uniformly fastened, the constant 0.188 (For SI: 1/1627) in the third term shall be modified accordingly.
| Click to view image | (Equation 23-1) |
| For SI: | Click to view image |
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).
en = Staple deformation, in inches (mm) [see Table 2305.2(1)].
Gt = Panel rigidity through the thickness, in pounds per inch (N/mm) of panel width or depth [see Table 2305.2(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).
[Delta] = The calculated deflection, in inches (mm).
[Sigma] (Delta;cX) = 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(1) en VALUES (inches) FOR USE IN CALCULATING DIAPHRAGM AND SHEAR WALL DEFLECTION DUE TO FASTENER SLIP (Structural I)a, c
| LOAD PER FASTENERb (pounds) | FASTENER DESIGNATIONS |
| 14-Ga staple x 2 inches long | |
| 60 | 0.011 |
| 80 | 0.018 |
| 100 | 0.028 |
| 120 | 0.04 |
| 140 | 0.053 |
| 160 | 0.068 |
| For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound =
4.448 N. a. Increase en values 20 percent for plywood grades other than Structural I. b. Load per fastener = maximum shear per foot divided by the number of fasteners per foot at interior panel edges. c. Decrease en values 50 percent for seasoned lumber (moisture content < 19 percent). |
TABLE 2305.2(2) VALUES OF Gt FOR USE IN CALCULATING DEFLECTION OF WOOD STRUCTURAL PANEL SHEAR WALLS AND DIAPHRAGMS
|
PANEL
TYPE |
SPAN
RATING |
VALUES OFGt (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
(inches) |
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 per inch = 0.1751
N/mm. a. Applies to plywood with five or more layers; for five-ply/three-layer plywood, use values for four ply. |
