![]() The house acts as a structural system resisting dead loads (weight of materials), live loads (weights imposed by use and occupancy), like snow loads and wind loads. This article will focus on how simple beams like joists and rafters react to loading. If, when the loads of the house are combined, the house weighs more than the soil can support – the house will sink until it reaches a point at which the soil can support the load. Remember when your science teacher said: every action has an opposite and equal reaction? Well every building load has an equal “reaction load”. The structural goal of a house is to safely transfer building loads (weights) through the foundation to the supporting soil. A complete analysis of wood’s mechanical properties is complex, but understanding a few basics of lumber strength will allow you to size joists and rafters with the use of span tables. Wood is naturally engineered to serve as a structural material: The stem of a tree is fastened to the earth at its base (foundation), supports the weight of its branches (column) and bends as it is loaded by the wind (cantilever beam). Lumber cut exclusively from today’s longleaf timber is also referred to as “new heart pine.Using span tables to size joists and rafters is a straight-forward process when you understand the structural principles that govern their use. Other variations on the theme include “old heart” and “river pine.” “Antique heart pine” or “reclaimed heart pine” refers to lumber from old growth Southern Pine, regardless of species, salvaged as timbers from old factories, mills or barns, or recovered as “sinker” logs from river bottoms. Consequently, longleaf pine may be in short supply while efforts are under way to increase its availability (visit Longleaf Alliance to find out more). Longleaf pine was not replanted as widely as other faster-growing species. Palustris …”īecause the two species share many characteristics (long needles, higher density), both slash and longleaf timber can be manufactured as longleaf lumber if minimum requirements like ring density are met under the rules. The rule states, “Longleaf lumber shall be produced only from Southern Pine tree species (botanical) of Pinus elliottii and P. However, SPIB adds another wrinkle to the heart pine puzzle. Longleaf lumber is so prized it merits a special quality classification within the grading rules. Of the 10 Southern Pine species, longleaf pine is most commonly referred to as “heart pine.” It is generally characterized by tighter growth rings, higher density, and greater proportion of heartwood. Instead, SPIB rules establish measurement guidelines so the lumber buyer and seller can agree on a specified percentage of heartwood required in each piece. However, there is no set ratio of heartwood to sapwood in the grading rules that defines heart pine lumber. Heart or all-heart lumber is free from sapwood throughout the piece. In the heart pine trade, the rule of thumb is “The redder the better.”Īccording to the special quality classifications of the Southern Pine Inspection Bureau grading rules, heart-face lumber is free from sapwood on the face side. Lumber cut from the heartwood of any Southern Pine species can be considered heart pine. It is more dense, and thus harder, than sapwood. Generally, heartwood can be distinguished from sapwood by its reddish color. Heartwood is the “dead” or dormant center of a tree surrounded by the living sapwood. Southern Pine lumber is composed of sapwood, heartwood, or a combination of the two. Forest Products Machinery & Equipment EXPO. ![]() Headers & Beams : Allowable Load Tables.Headers & Beams : Size Selection Tables. ![]()
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