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Building Design and Construction Handbook - Merritt - Ventech!

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10.6 SECTION TEN<br />

Use st<strong>and</strong>ard details wherever possible. Avoid specially designed <strong>and</strong> manufactured<br />

connecting hardware.<br />

Use as simple <strong>and</strong> as few joints as possible. Place splices, when required, in<br />

areas of lowest stress. Do not locate splices where bending moments are large,<br />

thus avoiding design, installation, <strong>and</strong> fabrication difficulties.<br />

Avoid unnecessary variations in cross section of members along their length.<br />

Use identical member designs repeatedly throughout a structure, whenever practicable.<br />

Keep the number of different arrangements to a minimum.<br />

Specify required design stresses to permit the widest range of products that can<br />

be used for a given design situation.<br />

Use wood products pressure treated with preservatives where service conditions<br />

dictate. Such treatment need not be used where decay or insect attack hazards<br />

do not exist. Fire-retardant treatments may be used to meet a specific flamespread<br />

rating for interior finish, but are not necessary for large-cross-sectional<br />

members that are widely spaced <strong>and</strong> have a natural resistance to fire because of<br />

their relatively large size.<br />

Instead of long, simple spans, consider using continuous or suspended spans or<br />

simple spans with overhangs.<br />

Select an appearance grade best suited to the project. Do not specify the highest<br />

quality appearance grade available for all members if it is not required.<br />

Table 10.2 may be used as a general guide to typical ranges of spans for roof<br />

<strong>and</strong> main floor framing members (excluding repetitive member joist <strong>and</strong> rafter applications).<br />

10.2 SECTIONAL PROPERTIES OF WOOD<br />

PRODUCTS<br />

Dressed sizes of sawn lumber are given in the grading rules of agencies that formulate<br />

<strong>and</strong> maintain such rules <strong>and</strong> in Table 10.3. The nominal <strong>and</strong> dressed sizes<br />

are developed in accordance with the American Softwood Lumber St<strong>and</strong>ard, Voluntary<br />

Product St<strong>and</strong>ard PS 20-94. These sizes are generally available, but it is<br />

good practice to consult suppliers before specifying sizes not commonly used to<br />

find out what sizes are on h<strong>and</strong> or can be readily secured.<br />

The supplement to the ‘‘National <strong>Design</strong> Specification� for Wood <strong>Construction</strong>’’<br />

published by the American Forest & Paper Association (formerly the National Forest<br />

Products Association) presents tables of section properties of st<strong>and</strong>ard dressed<br />

sawn lumber <strong>and</strong> glulam timber. St<strong>and</strong>ard finished sizes of structural glulam timber<br />

should be used to the extent that conditions permit. These st<strong>and</strong>ard finished sizes<br />

are based on lumber sizes given in Voluntary Product St<strong>and</strong>ard PS 20-94. Other<br />

finished sizes may be used to meet the size requirements of a design, or to meet<br />

other special requirements.<br />

For the manufacture of glulam nominal 2-in-thick lumber, surfaced to 1 3 ⁄8 in or<br />

1 1 ⁄2 in before gluing, is used to laminate straight members <strong>and</strong> curved members<br />

having radii of curvature within the bending-radius limitations for the species. Nominal<br />

1-in-thick lumber, surfaced to 3 ⁄4 in before gluing, may be used for laminating

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