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LH-Series Joists have been standardized in depths from 18 inches (460 mm) through 48 inches (1,200 mm), for spans through 96 feet (29,000 mm). DLH-Series Joists have been standardized in depths from 52 inches (1,300 mm) through 120 inches (3,000 mm), for spans up through 240 feet (73,000 mm).
Greek: the ridge height is 1 ⁄ 9 to 1 ⁄ 7 the span (an angle of 12.5° to 16°); Roman: the ridge height is 2 ⁄ 9 to 1 ⁄ 3 the span (an angle of 24° to 34°); Common: the rafter length is 3 ⁄ 4 the span (about 48°); Gothic: the rafters equal the span (60°); and; Elizabethan: the rafters are longer than the span (more than 60°). [7]
Sizes vary according to the I-joist's intended load and span. Depths can range from 9 + 1 ⁄ 4 to 24 inches (230–610 mm) and reach up to 80 feet (24 m) in length, although 40 to 42 feet (12–13 m) is more common.
There are approved formulas for calculating the depth required and reducing the depth as needed; however, a rule of thumb for calculating the depth of a wooden floor joist for a residential property is to take half the span in feet, add two, and use the resulting number as the depth in inches; for example, the joist depth required for a 14-foot ...
I-joists, I-beams engineered from wood with fiberboard or laminated veneer lumber, or both, are also becoming increasingly popular in construction, especially residential, as they are both lighter and less prone to warping than solid wooden joists. However, there has been some concern as to their rapid loss of strength in a fire if unprotected.
[5] [3] As a rule of thumb, the depth should be 1 ⁄ 24 of the span. [5] The width of the ribs is typically 130 mm (5 in) to 150 mm (6 in), and ribs usually have steel rod reinforcements. [5] The distance between ribs is typically 915 mm (3 ft). [3] The height of the ribs and beams should be 1 ⁄ 25 of the span between columns. [3]
Key: 1: queen posts, 2: tie beam, 3: straining beam, 4: principal rafters. A queen post truss has two principal rafters and two vertical queen posts. [5] The queen post truss extends the span, and combined with spliced joints in the longer members extends the useful span for trusses of these types.
In engineering, span is the distance between two adjacent structural supports (e.g., two piers) of a structural member (e.g., a beam). Span is measured in the horizontal direction either between the faces of the supports (clear span) or between the centers of the bearing surfaces (effective span): [1] A span can be closed by a solid beam or by ...