EWPAA Structural Plywood and LVL Design Manual - Engineered ...

10 Structural Plywood / LVL Gusseted Timber PortalFrames10.1 IntroductionPortals can be of rigid, two or three hinged construction as shown in FIGURE 10.1. The rigid portalminimises column / rafter cross-sectional dimensions but provides challenges regarding the development offull moment resistance at the column base. The three hinged portal results in maximum column / rafterdimensions and maximum bending moment having to be resisted at the portal eaves (haunch or knee)joint. The two hinged portal provides a suitable structural compromise thus eliminating the column baseconnection problem and the member oversizing by incorporation of a ridge moment joint.FIGURE 10.1: Common single storey, single spanning portal framesThe plywood or LVL gusseted timber portal, in its multitude of structural forms, provides an excellent solutionto a wide range of building requirements. Plywood or LVL gussets nailed to the framing elements at theeaves and ridge of the portal frame are economical, easy to fabricate and provide an effective method ofdeveloping moment resisting joints at these locations. The two main design components for structuralplywood or LVL gussets are:• sizing of the structural plywood / LVL gussets;• design of the nailed connection to transmit the applied column / rafter forces developed at the portaleaves and the rafter / rafter moment joint at the ridge.10.2 MaterialsPortal frame gussets can be fabricated from structural plywood or structural Laminated Veneer Lumber(LVL).Structural plywood produced in Australia and New Zealand is typically manufactured from a pine species;Radiata, Slash or Hoop Pine in Australia and Radiata Pine in New Zealand, with F8, F11 and F14 being themost readily available stress grades for these species. The most common sheet size for structural plywood is2400 x 1200 mm, but other lengths (2700, 1800) and widths (900) are also available. Suitable face veneergrades for gussets would be DD, or possibly CD where appearance is also a consideration. Structuralplywood is available in a range of thicknesses and constructions. 5 TABLE 5.3 in Chapter 5 of this Manualdetails standard structural plywood thicknesses and constructions. The construction or lay-up of the plywoodmust be specified in the gusset design, as AS 1720 utilises parallel ply theory in evaluation of the strengthcapacity of structural plywood loaded in-plane in bending. Therefore, thickness of cross-band veneers is notincluded in the overall structural plywood thickness used to evaluate gusset strength capacity.Structural Laminated Veneer Lumber manufactured in Australia and New Zealand is typically manufacturedfrom Radiata Pine. Strength capacities for LVL vary from manufacturer to manufacturer with each individualmanufacturer publishing their products specific structural properties. Properties are identified by themanufacturer’s brand name and this brand name needs to be included in any specification for structural LVLgussets. Structural LVL is available in widths up to 1200 mm and lengths up to 25m. Veneer grades for LVLare in accordance with the manufacturer’s specification, and are based on structural properties rather thanaesthetic considerations. Face veneer grades for LVL would be comparable to a plywood D or C quality face.Typical thicknesses for LVL are 35, 36, 45, 63 and 75 mm. Structural LVL is usually manufactured with nocross-bands, however when used as gussets, a cross-band immediately below the face veneers will improve122