A406.3.1 Horizontal Wood Diaphragms

Allowable shear values for existing horizontal wood diaphragms that require analysis under Section A403.10 are permitted to be taken from Table A4-A. The values in Table A4-A shall be used for allowable stress design. Design forces based on strength design shall be reduced to allowable stress levels before comparison with the limiting values in the table.

TABLE A4-A
ALLOWABLE VALUES FOR EXISTING MATERIALS

EXISTING MATERIALS OR CONFIGURATIONS OF MATERIALSa	ALLOWABLE VALUES
	´ 14.594 for N/m
1. Horizontal diaphragmsb 1.1. Roofs with straight sheathing and roofing applied directly to the sheathing 1.2. Roofs with diagonal sheathing and roofing applied directly to the sheathing 1.3. Floors with straight tongue-and-groove sheathing 1.4. Floors with straight sheathing and finished wood flooring with board edges offset or perpendicular 1.5. Floors with diagonal sheathing and finished wood flooring	-100 lbs. per ft. for seismic shear 250 lbs. per ft. for seismic shear 100 lbs. per ft. for seismic shear 500 lbs. per ft. for seismic shear 600 lbs. per ft. for seismic shear
2. Crosswallsb, c 2.1. Plaster on wood or metal lath 2.2. Plaster on gypsum lath 2.3. Gypsum wallboard, unblocked edges 2.4. Gypsum wallboard, blocked edges	Per side: 200 lbs. per ft. for seismic shear 175 lbs. per ft. for seismic shear 75 lbs. per ft. for seismic shear 125 lbs. per ft. for seismic shear
3. Existing footings, wood framing, structural steel and reinforced steel 3.1. Plain concrete footings 3.2. Douglas fir wood 3.3. Reinforcing steel 3.4. Structural steel	f 'c = 1,500 psi (10.3 MPa) unless otherwise shown by testsd Allowable stress same as D.F. No. 1d fs = 18,000 psi (124 MPa) maximumd fs = 20,000 psi (138 MPa) maximumd

1. Material must be sound and in good condition.
2. A one-third increase in allowable stress is not allowed.
3. Shear values of these materials may be combined, except the total combined value shall not exceed 300 pounds per foot.
4. Stresses given may be increased for combination of loads as specified in the building code.