Finite element modelling of castellated timber I-joists G. Baylor, A.M. Harte ⇑ Civil Engineering, College of Engineering and Informatics, National University of Ireland, Galway, Ireland highlights  Numerical modelling of a novel castellated timber I-joist is validated against experimental data.  Castellated joists shown to have bending stiffness 15–16% lower than equivalent solid–web joists.  A parameter study to determine the optimum castellation geometry is described. article info Article history: Received 10 October 2012 Received in revised form 2 May 2013 Accepted 12 May 2013 Available online 10 June 2013 Keywords: Timber structures I-joist OSB Finite element analysis Parameter study abstract This paper focuses on the structural analysis of innovative composite timber I-joists with castellated webs. The castellation process is carried out by cutting the web in a zig–zag pattern at mid-depth and then rejoining at an offset distance to create hexagonal holes. The flanges of the joists were made from Norway Spruce whilst the webs were made from oriented strandboard (OSB). The joists were analysed using the finite element method (FEM) with the component materials modelled as linear elastic orthotro- pic materials in both tension and compression. Good correlation was found between the experimental results and the FE simulations. The stiffness ratios obtained from test and FEA data (EI test /EI FEA ) were between 1.03 and 1.36 for the 241 mm joists and between 0.89 and 1.10 for the 305 mm joists. At peak load the FEA model predicted displacements of between 0.80 and 1.02 times that of the test for the 241 mm joists and between 0.98 and 1.16 times that of the test for the 305 mm joists. The validated FE models are compared to equivalent solid webbed joists to assess the effect the castellated webs have on their structural performance. A geometric parameter study was carried out to determine the optimum web opening geometry in terms of structural performance. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction The structurally engineered timber I-joist was successfully introduced into the construction market in the 1970s as an alterna- tive to larger-dimension solid sawn timber. Compared to solid sawn timber, I-joists are more efficient for structural use with a better environmental impact. The reduced amount of timber used in I-joists compared to solid structural timber make them lighter and easier to position on site. I-joists have the added benefits of reduced material resource impacts through the use of smaller diameter timber and lower embodied energy than solid timber joints. In addition, the advantage of a lower variability of performance and a better dimensional stability have led to extensive use in Europe and North America in both residential and commercial buildings e.g. for floor joist and roof applications such as sus- pended intermediate floors, suspended ground floors, purlins and rafters. The flanges are made from solid timber or laminated ve- neer lumber (LVL) and the web is made from oriented strandboard (OSB), plywood or particleboard [1,2]. Openings can be incorporated in the web to allow services to pass through. By accommodating services within the depth of the floors, the overall structural depth can be reduced or greater head- room provided. However, the presence of openings makes the stress distributions in the web more complicated and, depending on the configuration of the openings, can reduce the load carrying capability of the joist [3–5]. Manufacturers produce design guid- ance literature specifying permitted web hole requirements [6]. These guidance documents are generally restricted to circular or rectangular openings and limits are provided on the dimensions of the openings as well as restricting the positioning of openings to low shear areas. This paper addresses the concept of a timber I-joist using hex- agonal openings which result from the castellation manufacturing process, an example of which is seen in Fig. 1. Castellation is already well established for steel but has yet to be applied using timber. Castellated timber joists have a series of hexagonal shaped openings along the entire span, which provide flexibility in the 0950-0618/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conbuildmat.2013.05.076 ⇑ Corresponding author. E-mail addresses: gordonbaylor153@gmail.com (G. Baylor), annette.harte@nui galway.ie (A.M. Harte). Construction and Building Materials 47 (2013) 680–688 Contents lists available at SciVerse ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat