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

8 Structural Plywood Webbed Box Beam Design8.1 IntroductionStructural plywood webbed beams are a composite timber beam fabricated utilising structural plywoodas the web of the beam and a structural timber as the continuous beam flanges. The flange and webcomponents are usually connected with nails and/or glue. In this design chapter, information is given forthe design of nailed plywood webbed box beams. The design method is based on the information containedin the EWPAA Design Guide for Plywood Webbed Beams. The design aides included within this sectionfacilitate the design of box beams with structural plywood webs. However, these design aides will alsobe useful in estimating the required size of box beam components and other wood based flanges and plywoodweb stress grades.Structural plywood webbed beams are used in a wide variety of applications ranging from beams in residentialapplications, particularly lintel beams, through to rafters, columns, purlins and girts in industrial buildings andbox beam portal frames. Although plywood webbed beams will typically need to be deeper to be structurallyequivalent to a solid timber or steel beam, they have a number of useful advantages over solid timber andsteel beams. Plywood webbed beams are usually designed as parallel flange box, C or I-beams, howeverthey can also be designed and shaped to suit a particular application as tapered, curved or pitched beams.They are hollow and consequently light in weight, facilitating transportation and handling. They are easy tofabricate either as an independent component or, for nailed beams, in situ. Structurally the flanges aredesigned to carry the bending stresses while the webs transmit the shear. This achieves maximum structuralefficiency as well as economy in material usage and overall costs.FIGURE 8.1 shows the components of a structural plywood webbed box beam.PLANFIGURE 8.1: Plywood webbed box beam71