![]() ![]() If the beam were braced along its length it could support 20’ of roof tributary load (approximately 47,000 ft-lb applied moment). To understand the impact a lack of bracing can have on the required member size, consider a 3-ply 1.75” x 16” Microllam® LVL beam spanning 18’-3” and installed with only lateral support at the ends-a common situation for dropped garage headers. Beam Stability Factor, NDS Equation 3.3-6 ![]() Because wide beams have a larger L u, it is simpler and more cost effective to select a solid section Parallam® PSL for unbraced field conditions. Solid section beams like Parallam® PSL (which are inherently more laterally stable than multiple ply beams of the same width) often work without a size increase despite the lack of bracing. Accounting for this reduction can result in the need to increase the depth and/or width of a beam. This factor reduces the member’s allowable bending stress based on the actual unbraced length. Verifying the ability of a beam to support a load based on the maximum unbraced length is detailed in the National Design Specification® for Wood Construction (NDS) and requires calculating the beam’s stability factor (C L). Weyerhaeuser’s Forte® software provides the L u when a beam is designed. However, if the beam will not be fully braced, the designer must check the beam’s maximum allowable unbraced length (L u). In cases where a beam is fully braced (1 st set of pictures above) additional steps are not needed beyond the design checks for sufficient strength, acceptable deflection and bearing. The maximum unbraced length (Lu) must be checked when framing conditions do not continually brace a beam.Ī designer should consider the field conditions and whether the framing provides continuous lateral support to a beam. ![]() When a beam is not provided with sufficient bracing along its compression edge, the load carrying capability and stability may be affected. Common examples include dropped garage headers beams that are “upset” into a wall and, dropped beams installed to support concentrated loads from above. Some framing conditions, however, do not provide continuous lateral support to a beam. Framing conditions can provide bracing to beams. Design properties and allowable load tables are established assuming beams are braced. When a beam is directly attached to repeated framing members (joists or trusses) or fastened to sheathing in a floor system, the beam is continually braced for design purposes. Parallam® PSL provides superior strength and stiffness to address the more demanding conditions of many modern home designs. Not surprisingly, these changes have resulted in an increased demand for Engineered Wood Products (EWP), notably beams that can carry heavier loads across greater spans. Installation details can be found throughout TJ-9000 (EAST) TJ-9020 (WEST) - our beams, headers, and columns specifier’s guide.Īs with most things, this document has its limitations.Homes are increasingly being designed with more open spaces, larger rooms and atypical framing conditions. Required information to adequately size a member: Clear Span - the distance between the two inside surfaces of the span supports the distance that is unsupported, or simply, the opening.Bearing - a structural element that supports weight/loads.Dropped Beam - a beam that will be below the members it is supporting.Flush Beam - a beam that will be in the same elevation as the members it is supporting. ![]() For exterior/wet applications, see TJ-7102 The wood is placed in a depressurized holding tank that removes the air and replaces it with a preservative.
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