Timber stressed-skin panels: Design guidelines for Australian practice

The current edition of the Australian code for timber design, AS1720.1-1997 (Standards Australia, 1997), offers very minimal guidelines for the design of stressed-skin panel (SSP) structures. For example, it specifies checking of the stresses in the panels and in the glue line between the joists and panel, but there are no provisions concerning the contribution of the sheathing. In other words, AS1720.1-1997 recognises some composite action, but offers no directives for the approximation of the tributary width of the sheathing. The composite action - structural interaction between the joists and the sheathing - and the tributary width of the panel - portion of the sheathing acting compositely with the joists - are essential aspects of SSP floors. They govern the characteristics of the cross-section, and the strength and the serviceability of the structures. As such, ignoring one or both of these aspects leads to unsatisfactory design. Because of these factors, there is a need to review the design guidelines of AS1720.1-1997 in order for appropriate design of SSP floors to be undertaken. To this end, this paper puts forward a design procedure and proposes, in the form of an amendment to Section 5 of AS1720.1-1997, to include these directives in a future edition of the design code. The design procedure discussed herein is thorough in scope and straightforward in application. It addresses the composite characteristics of SSP structures composite action and tributary width of the sheathing. It provides clear guidelines for the assessment of both aspects. It also imposes a systematic verification of the different stresses experienced by the structure. This particular section of the design procedure considers both AS1720.1-1997 and Eurocode 5 (European Committee for Standardisation, 1995). In addition, a method to account for the two-way action ability of SSP structures is also proposed in the design procedure, which includes two equations derived by Gerber (2007). For defined applications, acceptable assessments of the load distribution in SSP systems are achieved with these two equations for loading on an exterior and interior joist, respectively.