Changes to the 2015 National Design Specification (NDS) for Wood Construction and the Inclusion of Cross-Laminated Timber

摘要

The 2015 Edition of the National Design Specification~® (NDS~®) for Wood Construction was recently published. The updated standard designated ANSI/AWC NDS-2015 was approved as an ANSI American National Standard on September 30, 2014 (Figure 1). The 2015 NDS was developed by the American Wood Council's (AWC) Wood Design Standards Committee and is referenced in the 2015 International Building Code (IBC). This paper will discuss the significant changes from the 2012 NDS to the 2015 NDS most of which include provisions for Cross Laminated Timber. The NDS has been around since 1944 when it was originally published by the National Lumber Manufacturers Association. AWC and its predecessors have been ANSI-accredited standards developers since 1992. The 1991 NDS received inaugural ANSI approval in October 1992. The NDS defines the methods to be followed in structural design with the following wood products: visually graded lumber, mechanically graded lumber, structural glued laminated timber, timber piles, timber poles, prefabricated wood I-joists, structural composite lumber, wood structural panels, and cross-laminated timber. It also defines the practice to be followed in the design and fabrication of single and multiple fastener connections using the fasteners described in the specification. Primary changes to the 2015 NDS are listed here and major topics are subsequently covered in more detail: 1. Incorporation of cross-laminated timber (CLT) in several chapters of the NDS, including a new product chapter specific to CLT 2. Added terminology for laminated strand lumber and oriented strand lumber 3. Clarification that withdrawal design values for lag screws excludes the length of the tapered tip 4. Inclusion of char rates for CLT and structural composite lumber 5. Relocation of reference to Special Design Provisions for Wind and Seismic (SDPWS).